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Hydrogen peroxide (H2O2) is gaining recognition as an eco-friendly and highly effective algicide for combating cyanobacterial blooms. This study investigates the algicidal potential of H2O2 catalyzed by both inorganic and organic iron. Our findings indicate that inorganic iron (FeSO4) shows minimal catalytic activity on H2O2 under varying light conditions. In contrast, organic iron, specifically the combination of H2O2, EDTANaFe, and light irradiation, demonstrates significant algicidal effects. The optimal dosages were identified as 10 mg/L for H2O2 and 3 mg/L for Fe3+.The limited efficacy of inorganic iron stems from the transformation of Fe2+ to Fe3+ ions via the Fenton reaction. Under neutral conditions, Fe3+ ions precipitate as large-sized goethite, which adheres to the extracellular polymeric substances (EPS) of cyanobacterial cells, thereby hindering H2O2 catalysis and hydroxyl radical (·OH) formation in natural waters. Conversely, the combination of light radiation and organic iron salts greatly enhances the algicidal efficiency of H2O2. This synergy accelerates H2O2 decomposition and facilitates the production of a substantial amount of OH radicals by altering the Gibbs free energy. Thus, bright and sunny conditions, particularly in the afternoon, are crucial for effectively combating cyanobacterial blooms using Fenton-like reagents. The methodology presented in this study offers a viable solution to global cyanobacteria bloom issues and elucidates the mechanisms driving its efficacy. [ABSTRACT FROM AUTHOR] more...

The expanding impact of algal blooms on marine areas poses a severe threat to the sustainable development of aquaculture, human health, and the ecological safety of coastal areas. To address this issue, the exploration of natural algicidal compounds with high efficiency, selectivity, and environmental friendliness has gained attention as potential substances for algae removal. However, the integration of related work still needs to be improved. Therefore, an in-depth study of algicidal strategies and applications of algicidal compounds for biodiversity has become crucial. Here, we aim to consolidate the current advancements in research on the sources and types of algicidal compounds. We also delve into various algicidal strategies, including the damage inflicted on algal structures, inhibition of photosynthesis, effects on oxidative damage, and impacts on gene expression. Additionally, we highlight practical applications of algicidal compounds, taking into account their specificities and limitations. This review contributes to the protection of marine biodiversity and the promotion of sustainable environmental development. Furthermore, we provide recommendations for future research on algicidal compounds to overcome existing barriers. By doing so, we hope to offer valuable references for researchers engaged in further studies on managing algal outbreaks. • The integration of natural algicidal compounds lacks a systematic review. • Strategies and applications of algicidal compounds for the control of harmful algal species are comprehensively reported. • Make recommendations for research to overcome current barriers and inform future research on algal outbreak management. [ABSTRACT FROM AUTHOR] more...

This study deals with the antialgal properties of allelochemicals present in 3-plants (Mallotus philippensis (Lam.) Muell Arg., Melia azedarach L., Mentha royleana Wall. ex Benth and Raphanus sativus L.). The methanolic leaf extracts of these plants were applied on Chlamydomonas reinhardtii Dangeard to find their antialgal properties. High Performance Liquid Chromatography (HPLC) was used to identifiy and quantify the allelochemicals present in these plants to ascertain their efficacy for growth inhibition of algae. Leaf extracts of plants significantly inhibited the growth of Chlamydomonas reinhardtii Dangeard (p <0.05). The p value for these plant species were: Mentha royleana Wall. ex Benth (p <0.05), Melia azedarach L. (p <0.05), Mallotus philippensis (Lam.) Muell Arg (p <0.01) and Raphanus sativus L. (p <0.01); indicating that number of cells of Chlamydomonas reinhardtii Dangeard were significantly inhibited. The most abundant allelochemicals identified by HPLC in M. royleana were caffeic acid (4.67 µg/ml) followed by rutin, trans-ferulic acid and naringin. The trans-ferulic acid was detected only in Mallotus philippensis (Lam.) Muell Arg but rutin was found in most plants. Most of the allelochemicals were found in Mentha royleana, hence, its extract was comparatively more inhibitory to algal growth. The inhibitory effects of methanolic leaf extracts on growth of C. reinhardtii strongly supports the hypothesis that these test plants have ample potential for use as algaecides due to presence of allelochemicals. [ABSTRACT FROM AUTHOR] more...

Algicidal bacteria have been frequently isolated from algal blooming areas. However, knowledge regarding the microbial communities coexisting with microalgae and their potential application in preventing harmful algal blooms (HABs) is limited. In this study, we investigated the composition of the microbial community coexisting with harmful alga Karenia mikimotoi and its responses to algal control via nutrient stimulation or by adding algicidal strain in microcosms. The microorganisms inhabiting the K. mikimotoi culture consisted of 24 identified phyla, including dominant Proteobacteria (relative abundance 76.24%±7.28%) and Bacteroidetes (22.67%±8.32%). Rhodobacteraceae, Phaeodactylibacter, and Maritimibacter predominated during the algal cultivation. Both the added nutrient and fermentation broth of algicidal strain Pseudoalteromonas QF1 caused a massive death of K. mikimotoi and substantial changes in the coexisting microbial community, in which Rhodobacteraceae and Phaeodactylibacter significantly decreased, while Halomonas and Alteromonas increased. Core operational taxonomic units (OTUs) analysis indicated that 13 OTUs belonging to Rhodobacteraceae, Maritimibacter, Marivita, Nisaea, Phaeodactylibacter, Citreicella, Halomonas, Alteromonas, Marinobacter, Muricauda, and Pseudoalteromonas dominated the changes of the microbial communities observed in the K. mikimotoi culture with or without treatments. Collectively, this study indicated that microbial community inhabiting K. mikimotoi culture includes potential algicidal bacteria, and improves our knowledge about microbial community succession during biocontrol of K. mikimotoi via nutrient stimulation or by adding isolated algicidal strains. [ABSTRACT FROM AUTHOR] more...

Harmful algal blooms (HABs) affect both freshwater and marine systems. Laboratory experiments suggest an exudate produced by the bacterium Shewanella sp. IRI-160 could be used to prevent or mitigate dinoflagellate blooms; however, effects on non-target organisms are unknown. The algicide (IRI-160AA) was tested on various ontogenetic stages of the copepod Acartia tonsa (nauplii and adult copepodites), the blue crab Callinectes sapidus (zoea larvae and megalopa postlarvae), and the eastern oyster Crassostrea virginica (pediveliger larvae and adults). Mortality experiments with A. tonsa revealed that the 24-h LC50 was 13.4% v/v algicide for adult females and 5.96% for early-stage nauplii. For C. sapidus, the 24-h LC50 for first-stage zoeae was 16.8%; results were not significant for megalopae or oysters. Respiration rates for copepod nauplii increased in the 11% concentration, and in the 11% and 17% concentrations for crab zoeae; rates of later stages and oysters were unaffected. Activity level was affected for crab zoeae in the 1%, 11%, and 17% treatments, and for oyster pediveliger larvae at the 17% level. Activity of later stages and of adult copepods was unaffected. Smaller, non-target biota with higher surface to volume could be negatively impacted from IRI-160AA dosing, but overall the taxa and stages assayed were tolerant to the algicide at concentrations required for dinoflagellate mortality (EC50 = ~ 1%). [ABSTRACT FROM AUTHOR] more...

The study is aimed to evaluate the algicidal activity, antioxidant and cytotoxicity properties of the extract by ethyl acetate of algicidal bacteria Loktanella sp. Gb03 UKMGb03A (KU199217)). The algicidal activity of the ethyl acetate extract of Loktanella sp. Gb03 was assessed against toxic dinoflagellate Coolia malayensis. The cytotoxicity property was determined by MTT assay and antioxidant activity was detected by DPPH radical scavenging activity. The results of algicidal activity assay showed that the Loktanella sp. Gb03 extract possesses algicidal activity against toxic dinoflagellate Coolia malayensis. The Loktanella sp. Gb03 showed higher antioxidant activity compare to standard antioxidant ascorbic acid. In addition, Loktanella sp. Gb03 exhibited low cytotoxicity. However, the Loktanella sp. Gb03 has strong algicidal activity and antioxidant activities that are potent associated with its ethno medicinal values. [ABSTRACT FROM AUTHOR] more...

The impacts of harmful algal blooms on human health, tourism, fisheries and ecosystems have increased in recent decades. Eutrophication and the feared climate change are believed to further challenge authorities and those whose activity depends on coastal resources. While in most of the affected countries, regulatory steps have been taken to protect consumers of contaminated food, there has been an unequal focus on management systems. Some countries such as EEUU and Canada have focused on monitoring and prediction programs, whereas others (e.g. Korea, China) have relied on direct control of blooms in the sea. Here, we review current control methods for HABs including their fundamentals and the last scientific advances. A thorough revision of all considered approaches so far has been included. Ecological studies of the impact of the countermeasures were also considered. [ABSTRACT FROM AUTHOR] more...

Highlights • A bacterium (FDHY-03) was isolated in a bloom of Prorocentrum donghaiense. • FDHY-03 strain showed high algicidal rate against P. donghaiense. • FDHY-03 lysed P. donghaiense cells from megacytic growth zone. • FDHY-03 lysed P. donghaiense cells by digesting cell wall polysaccharides. Abstract The relationship between algicidal bacteria and harmful-algal-bloom-forming dinoflagellates is understudied and their action modes are largely uncharacterized. In this study, an algicidal bacterium (FDHY-03) was isolated from a bloom of Prorocentrum donghaiense and the characteristics of its action against P. donghaiense was investigated at physiological, molecular, biochemical and cytological levels. 16S rDNA sequence analysis placed this strain in the genus of Alteromonas in the subclass of γ-proteobacteria. Algicidal activity was detected in the bacterial filtrate, suggesting a secreted algicidal principle from this bacterium. Strain FDHY-03 showed algicidal activity on a broad range of HAB-forming species, but the greatest effect was found on P. donghaiense , which showed 91.7% mortality in 24 h of challenge. Scanning electron microscopic analysis indicated that the megacytic growth zone of P. donghaiense cells was the major target of the algicidal action of FDHY-03. When treated with FDHY-03 culture filtrate, P. donghaiense cell wall polysaccharides decreased steadily, suggesting that the algicidal activity occurred through the digestion of cell wall polysaccharides. To verify this proposition, the expression profile of beta-glucosidase gene in FDHY-03 cultures with or without P. donghaiense cell addition was investigated using reverse-transcription quantitative PCR. The gene expression level increased in the presence of P. donghaiense cells, indicative of beta-glucosidase induction by P. donghaiense and the enzyme's role in this dinoflagellate's demise. This study has isolated a new bacterial strain with a strong algicidal capability, documented its action mode and biochemical mechanism, providing a potential source of bacterial agent to control P. donghaiense blooms. [ABSTRACT FROM AUTHOR] more...

The use of bdellovibrios has been regarded as an alternative to control multidrug-resistant pathogens and fish bacteriosis. However, scarce information is available on the potential of bdellovibrios in the presence of copper sulfate, which is an algicide widely used to treat cyanobacterial blooms in aquaculture. In the present study, the effects of copper sulfate at sublethal and lethal levels (0.1 and 1.0 mg·L−1) on Bdellovibrio sp. strain BDF-H16 were evaluated. The growth of Bdellovibrio sp. strain BDF-H16 was significantly promoted by both concentrations of copper sulfate, but less so by the lethal concentration. The bacteriolysis of gibel carp-pathogenic Aeromonas hydrophila by Bdellovibrio sp. strain BDF-H16 was also stimulated by copper sulfate in both solid and liquid media. However, Bdellovibrio sp. strain BDF-H16 with 0.1 mg·L−1 copper sulfate clearly inhibited infection of gibel carps by A. hydrophila better than Bdellovibrio sp. strain BDF-H16 with 1.0 mg·L−1 copper sulfate did. [ABSTRACT FROM AUTHOR] more...

Plant allelochemicals are considered as the source of effective, economic and friendly-environmental algaecides. To uncover the anti-algal activities of Cinnamomum camphora fresh leaves and their main algicidal agents, we investigated the inhibitory effects of water and methanol extracts from C. camphora fresh leaves on Microcystis aeruginosa and Chlamydomonas reinhardtii cell growth, analyzed the composition of the water and methanol extracts, and determined the main compounds in extracts on the growth of the two algae and their anti-algal mechanism from photosynthetic abilities. Water and methanol extracts from C. camphora fresh leaves can inhibit M. aeruginosa and C. reinhardtii cell growth, and methanol extracts showed stronger inhibitory effects, due to their more compounds and higher molar concentration. There were 23 compounds in the water extracts, mainly including terpenoids, esters, alcohols, and ketones. Compared to the water extracts, 9 new compounds were detected in the methanol extracts, and the molar concentration of total compounds in methanol extracts increased by 1.3 folds. Camphor, α-terpineol and linalool were 3 main compounds in the water and methanol extracts. Their mixture (1: 3: 6) and individual compound showed remarkable inhibition on M. aeruginosa and C. reinhardtii cell growth. The degradation of photosynthetic pigments and the reduction of maximum quantum yield of photosystem II (PSII) photochemistry, coefficient of photochemical quenching as well as apparent electron transport rate in C. reinhardtii cells aggravated gradually with increasing the concentration of the mixture and individual compound, while the non-photochemical dissipation of absorbed light energy increased gradually, which led to the decline of photosynthetic abilities. This indicated that camphor, α-terpineol and linalool were 3 main algicidal agents in C. camphora fresh leaf extracts, and they inhibited algal growth by inducing photosynthetic pigment degradation and declining PSII efficiency. Therefore, C. camphora fresh leaf extracts and their main components have potential utilization values as algaecides. [ABSTRACT FROM AUTHOR] more...

Algicidal bacteria associated with Karenia mikimotoi have been isolated, yet the distribution of the algicidal bacteria has been rarely studied. Here, we postulated and demonstrated that terrestrial environment harbors diverse algicidal bacteria, which can survive in seawater along water flowing into marine and suppress Karenia mikimotoi . In summary, 9 and 5 bacteria with algicidal activity on Karenia mikimotoi were isolated from seawater and estuarine soil, respectively. Similar with the marine bacteria ( Alteromonas sp., Halomonas sp., Marinobacter sp., Paracoccus sp., Rhodobacteraceae , Idiomarina sp.), the soil strains ( Pseudoalteromonas sp. and Flavobaterium sp.) showed high mortality in Karenia mikimotoi with the inhibitory rate of 87% and 93.5%, respectively, after two days co-cultivation. Algicidal activity of the two strains was detected in the cell-free filtrate not in bacterial cells. The results suggest that algicidal bacteria associated with Karenia mikimotoi widely exist in terrestrial and marine environments, and have application potential on controlling Karenia mikimotoi . [ABSTRACT FROM AUTHOR] more...

To find the potential algicidal microorganisms and apply them to prevent and terminate harmful algal blooms (HABs), we isolated an actinomycete U3 from Mangrove, which had a potent algicidal effect on the harmful alga Heterosigma akashiwo . It could completely lyse the algal cells by producing active compounds, which were highly sensitive to high temperature and strong alkaline, but resistant to acid. One μg/mL of crude extract of the fermentation supernatant could kill 70% of H. akashiwo cells in 3 d. Unlike most of the other known algicidal Streptomyces , U3 showed strong ability of proliferation with the algal inclusion as the nutrient source. The washed mycelial pellets also gradually exhibited significant algicidal effect during the visible growth in the algal culture. It suggests that U3 could efficiently absorb nutrients from algal culture to support its growth and produce algicidal compounds that might cause the autophagy of algal cells. Therefore, applying U3, as a long-term and environmentally friendly bio-agent to control the harmful blooms of H. akashiwo , would be effective and promising. And the decrease of bioavailable DOM and increase of bio-refractory DOM during the algicidal process of U3 provided new insights into the ecological influence of algicial microorganisms on marine ecosystem. [ABSTRACT FROM AUTHOR] more...

This study examined the ability of acidic and neutral/alkaline fractions of a methanolic extract from giant reed ( Arundo donax ) and of two of its constituents, gramine and skatole, to inhibit growth of the ichthyotoxic golden alga (Prymnesium parvum ) in batch culture. For this study, growth suppression was defined as inhibition of maximum cell density, algicidal activity as early occurrence of negative growth, and algistatic activity as lack of net growth. The acidic fraction did not affect algal growth. The neutral/alkaline fraction showed growth-suppressing and algicidal activities but no signs of algistatic activity – namely, cells in cultures surviving a partial-algicidal exposure concentration (causing transient negative growth) were later able to initiate positive growth but at higher concentrations, algicidal activity was full and irreversible. Gramine suppressed growth more effectively than skatole and at the highest concentration tested, gramine also showed partial-algicidal and algistatic activity. While the partial-algicidal activities of the neutral/alkaline fraction and of gramine were short-lived (≤6 days) and thus may share similar mechanisms, algistatic activity was unique to gramine and persisted for >3 weeks. Given gramine’s reported concentration in the neutral/alkaline fraction, its corresponding level of algicidal activity is much lower than the fraction’s suggesting the latter contains additional potent algicides. Inhibition of maximum cell density by all test compounds was associated with reductions in exponential growth rate, and in the case of the neutral/alkaline fraction and gramine also reductions in early (pre-exponential) growth. These results indicate that giant reed is a potential source of natural products to control golden alga blooms. Giant reed is an invasive species in North America, thus also providing incentive for research into strategies to couple management efforts for both species. [ABSTRACT FROM AUTHOR] more...

In search of an ecofriendly algaecide, aqueous extracts of two medicinal plants, Thymus satureioides Coss and Artemisia herba alba L., were assessed for antialgal activity against Microcystis aeruginosa. An experiment was designed using five treatments (1%, 0.75%, 0.5%,0.25% and 0.1%). The growth of M. aeruginosa, morphological modifications and photosynthetic pigments (chlorophyll a and carotenoids) on exposure to the extracts were explored. Also, phytochemical parameters in the extracts were analyzed to reveal the potential allelochemical compounds. The results showed that both T. satureioides and A. herba alba extracts inhibited the growth of M. aeruginosa in a concentration-dependent way. After 8 days of treatment, the highest inhibition rates reached were 95%, 93% and 88.58% and for T. satureioides and A. herba alba aqueous extracts, respectively. Chlorophyll a and carotenoid concentrations in cultures decreased especially in the 1% treatment group. Several morphological changes were observed in the treatment group compared to the controls. It was concluded that M. aeruginosa growth was suppressed by the potentially allelochemical compounds and probably by other allelochemical substances in aqueous extracts. Our results illustrated that both T. satureioides and A. herba alba extracts are able to control Microcystis blooms and these may be recommended as a remedy for contamination of water bodies by harmful blooms. [ABSTRACT FROM AUTHOR] more...

Abstract: The interest and use of variations of partitioned aquaculture systems (PAS) by the catfish farming industry in the southeastern USA continues to grow. Split‐pond systems, one type of PAS, are designed to improve the management of dissolved oxygen levels and fish waste products (e.g., ammonia) compared with conventional earthen ponds that have been used for many decades. While recent studies of split‐pond systems have focused on design, water flow rates, and management practices, there has not been any assessment of the occurrences and intensities of common “off‐flavor” episodes in these split‐ponds. For the current study, pond water samples were collected from split‐ponds at a commercial fish farm in western Alabama and at a research facility in western Mississippi approximately every 3–4 weeks during the fish grow‐out period (May to November) during 2014 and 2015. In addition, fillet samples from hybrid catfish (Channel Catfish Ictalurus punctatus × Blue Catfish Ictalurus furcatus) were obtained in late summer and autumn from these same split‐ponds. Concentrations of the “earthy” and “musty” off‐flavor compounds geosmin and 2‐methylisoborneol (MIB), respectively, in water and fillet samples were determined. Sensory analysis was also performed on catfish fillets collected during 2014. The highest geosmin and MIB concentrations detected in split‐pond water during the study were 898 and 22,651 ng/L, respectively. Geosmin and MIB concentrations in split‐pond water were often higher in summer and autumn, and concentrations were similar to those reported previously for conventional ponds. The highest geosmin and MIB concentrations detected in fillets during the study were 1,712 and 29,851 ng/kg, respectively. Concentrations of these compounds in fillets and the description and intensities determined via sensory analysis were similar to those reported previously for off‐flavor catfish from conventional ponds. Accordingly, catfish farmers using split‐ponds can use similar management approaches as those used to mitigate earthy and musty off‐flavor problems in catfish raised in conventional ponds (e.g., applications of algicides). [ABSTRACT FROM AUTHOR] more...

Algicidal bacteria offer a promising option for killing Microcystis aeruginosa , one notorious cyanobacteria causing harmful algal blooms. In this study, Citrobacter sp. R1 presented high algicidal activity (81.6 ± 2.2%, 72 h) against M. aeruginosa when cultured using glucose, while it showed no algicidal activity (0 ± 3.4%) when cultured using wheat bran, suggesting that appropriate carbon source is crucial for algicidal bacteria in killing M. aeruginosa . The underlying algicidal mechanism of strain R1 was explored by studying the effect of different carbon sources (glucose and wheat bran) on its key algicidal gene expression and total protein translation. While the glycogen synthase gene ( glgA ), cloned from strain R1 via transposon mutagenesis, was for the first time related to algicidal activity, its transcriptional level was not positively correlated with the algicidal activity of strain R1. We found that, the translation of total protein of strain R1 was relatively less when cultured with glucose, compared to growth with wheat bran. This indicated that the functional algicidal gene of strain R1 exerts its algicidal activity at protein translational level. These findings not only reveal the importance of appropriate carbon source for strain R1 for controlling M. aeruginosa , but also bring insights into its underlying algicidal mechanism. [ABSTRACT FROM AUTHOR] more...

In this study, a series of rhodanine derivatives containing various substituents was synthesized and tested for in vitro algicidal activity. Among the tested substituent groups, phenyl substituents with halogen groups showed good inhibitory potency. Furthermore, the compound with chlorine at the C2 position of the phenyl ring exhibited a higher algicidal effect than the compound with chlorine at the C3 position of the phenyl ring. Among the various rhodanine derivatives tested, 5-(2,4-dichlorobenzylidene)- rhodanine (compound 20) was the most potent inhibitor against M. aeruginosa with a lethal concentration 50 (LC) value of 0.65 μM and Selenastrum capricornutum with an LC value of 0.82 μM. To verify the feasibility of their use in ecosystems, 25 h of acute ecotoxicity tests were carried out for three derivatives against Danio rerio and Daphnia magna. No mortality was observed in groups exposed to 2.0 μM of compound 20 after 100 h of exposure. Moreover, a survival rate of 100% was observed in D. magna exposed to 2 μM of compound 20 for 100 h. Overall, the results show that rhodanine derivatives are a possible method for controlling and inhibiting harmful algal blooms. [ABSTRACT FROM AUTHOR] more...

In both freshwater and marine ecosystems, phytoplankton are the most dominant primary producers, contributing substantially to aquatic food webs. Algicidal bacteria that can associate to microalgae from the phytoplankton have the capability to control the proliferation and even to lyse them. These bacteria thus play an important role in shaping species composition in pelagic environments. In this review, we discuss and categorise strategies used by algicidal bacteria for the attack on microalgae. We highlight the complex regulation of algicidal activity and defence responses that govern alga-bacteria interactions. We also discuss how algicidal bacteria impact algal physiology and metabolism and survey the existing algicidal metabolites and enzymes. The review illustrates that the ecological role of algicidal bacteria is not yet fully understood and critically discusses the challenges in obtaining ecologically relevant data. [ABSTRACT FROM AUTHOR] more...

Eutrophication with a large number of Microcystis aeruginosa commonly occurs worldwide, thereby threatening the aquatic ecosystem and human health. In this study, four kinds of algicides were tested to explore their influence on cell density and chlorophyll-a of M. aeruginosa. Results showed that aluminum silicate agent, which inhibited more than 90% cell growth compared with the control group, demonstrated the strongest inhibition effect immediately on M. aeruginosa growth. Furthermore, the production and release of microcystin (MC)-LR were investigated. Aluminum silicate, CuSO, and Emma-11 were more effective than pyrogallic acid in disrupting the cells of M. aeruginosa, thereby increasing the extracellular MC-LR concentration. Aluminum silicate caused the highest extracellular MC-LR concentration of more than 45 mg·L. Biotoxicity was also detected to evaluate the environmental risks of MC-LR release, which were related to the usages of different algicides. Extracellular MC-LR concentration mostly increased when the biotoxicity of algae solution increased. The experiments were also designed to reveal the effects of physical conditions in riverways, such as natural sunlight, aeration and benthal sludge, on MC-LR degradation. These findings indicated that UV rays in sunlight, which can achieve a MC-LR removal efficiency of more than 15%, played an important role in MC-LR degradation. Among all the physical pathways of MC-LR removal, benthal sludge adsorption presented the optimal efficiency at 20%. [ABSTRACT FROM AUTHOR] more...

Filamentous mat-forming cyanobacteria are increasingly impairing uses of freshwater resources. To effectively manage, a better understanding of control measures is needed. Copper (Cu)-based algaecide formulations are often applied to reactively control nuisance cyanobacterial blooms. This laboratory research assessed typical field exposure scenarios for the ability of Cu to partition to, and accumulate in Lyngbya wollei. Exposure factors (Cu concentration × duration) of 4, 8, 16, 24, 32 h were tested across three aqueous Cu concentrations (1, 2, 4 ppm). Results indicated that internally accumulated copper correlated with control of L. wollei, independent of adsorbed copper. L. wollei control was determined by filament viability and chlorophyll a concentrations. Similar exposure factors elicited similar internalized copper levels and consequent responses of L. wollei. Ultimately, a 'concentration-exposure-time' (CET) model was created to assist water resource managers in selecting an appropriate treatment regime for a specific in-water infestation. By assessing the exposure concentration and duration required to achieve the internal threshold of copper (i.e., critical burden) that elicits control, water management objectives can be achieved while simultaneously decreasing the environmental loading of copper and potential for non-target species risks. [ABSTRACT FROM AUTHOR] more...

Leaf aqueous (LA) extracts of medicinal plants Achillea ageratum L. and Origanum compactum Benth. were tested to explore their potential algicidal effects on Microcystis aeruginosa. The growth of M. aeruginosa and cell morphology changes in response to LA extracts was investigated. The concentrations of total phenols, total flavonoids, and total tannins in LA extracts were analyzed to reveal the potential allelochemical compounds. The results demonstrate that both A. ageratum and O. compactum LA extracts inhibit M. aeruginosa growth in a concentration-dependent way. For both LA extracts, the highest inhibition rate exceeded 80% since the fifth day of exposure. The induction of inhibition effects was translated by a decrease in photosynthetic pigments (chlorophyll-a and carotenoids) and with other morphological modifications. Our results illustrate that both A. ageratum and O. Compactum LA extracts can offer an effective solution for control of Microcystis blooms, and these are recommended in the restoration of aquatic environments contaminated by these types of algal blooms. [ABSTRACT FROM AUTHOR] more...

In previous studies, naphthoquinone (NQ) compounds have been shown to be effective, selective, and ecologically safe algicides for controlling harmful algal blooming species (HABs) or winter bloom species, such as Stephanodiscus hantzschii . However, there are no reports on NQ-based algicides for use with cyanobacterial blooming species. In this study, we developed 31 NQ compounds to investigate algicides for mitigating cyanobacterial blooms. In addition, to better apply these compounds in the field, we reduced the number of production steps to develop a cost-effective algicide. In preliminary testing, we screened NQ compounds that showed the best algicidal activity on target cyanobacteria, including Aphanizomenon , Dolichospermum , Microcystis , Oscillatoria, and Nostoc species. The compound NQ 2-0 showed the highest algicidal activity (90%) at a low concentration (≥1 μM) on target algae. These were very limiting algicidal effects of 1 µM NQ 2-0 observed against non-target algae, such as diatoms ( Stephanodiscus hantzschii, Cyclotella meneghiniana, Synedra acus, and Aulacoseira granulata ) or green algae ( Cosmarium bioculatum and Scenedesmus quadricauda ), and the effect did not exceed 15–25% (except against S. quadricauda ). NQ 2-0 (1 μM) showed no eco-toxicity, as represented by the survival rates of Pseudokirchneriella subcapitata (100%) , Daphnia magna (100%), and Danio rerio (100%). Additionally, a chronic eco-toxicity assessment showed no toxicity toward the survival, growth or reproduction of D. magna . Moreover, NQ 2-0 quickly dissipated from field water samples and had a half-life of approximately 3.2 days. These results suggest that NQ 2-0 could be a selective and ecologically safe algicide to mitigate harmful cyanobacterial blooms. [ABSTRACT FROM AUTHOR] more...

Prototheca species have increasingly been reported to be opportunistic pathogens that cause mastitis in dairy herds, and it poses an emergent problem because at present, there are no effective therapies for the treatment of protothecal mastitis. This study investigated the in vitro algicidal effect of guanidine on 75 Prototheca zopfii genotype 2 strains isolated from 75 cases of clinical and subclinical bovine mastitis. All strains were susceptible to guanidine in vitro with minimal algaecide concentrations ranging from 0·001 to 0·035%. Guanidine is known to have a high microbicidal effect and is considered to be a new generation microbicidal compound. It is not toxic to human mucous membranes and conjunctivas at low concentrations and has been used as a disinfectant in swimming pools and as an antiseptic for human wounds. The algicidal action of guanidine at low concentrations indicates that it could be an alternative disinfectant or antiseptic for cleaning of the dairy environment and milking equipment, in pre- and postdipping solutions, in the chemical dry therapy of bovine teats and even in the intramammary therapy of P. zopfii infections. This is the first report of the in vitro algicidal effect of guanidine on P. zopfii strains of animal origin. Significance and Impact of the Study Prototheca zopfii genotype 2 is an opportunistic pathogen of bovine mastitis. To date, no effective therapies against protothecal mastitis have been developed. The in vitro algicidal effect of guanidine on 75 P. zopfii genotype 2 strains isolated from cows revealed that all of the isolates were susceptible to the compound at low concentrations, which indicates that guanidine may be used as an antiseptic/disinfectant for dairy milking equipment, in pre- and postdipping solutions, and as a chemical dry therapy or an intramammary therapy. This study describes the in vitro algicidal effect of guanidine on P. zopfii for the first time. [ABSTRACT FROM AUTHOR] more...

To study ihe control effect of algicidal bacteria on blue-green algal blooms in natural conditions, three algicidal bacterial strains were osed to make a compound algal inhibiting agent, and the removal effects of the algal inhioiting agent on algae, nitrogen, phosphorus, organic matter, aid chlorophyll a in Chendian pool and Oiangwei pool of Qi.ancreng Park n Jinan City were analyzed. The resi-lts show that the algal inhibiting agent could eliminate the blue-green algal blooms. 54 days later, chlorophyll a content in the water bod es reduced to below 0.06 mp/L, and both CODc. and BOD5 decreased significantly. NH,"-N and TP content were lower than 2 and 0.05 rng/L respectively. The removal rate of COD was slightly low (33%48%), and the removal rales of other i-dicators were higher fan 60%, It is clearly seen that the algal nhibiting agent could quickly cl minatc the algal blooms and had a notaolo effect on the recovery of the outrop-ic water bodies. [ABSTRACT FROM AUTHOR] more...

Quorum sensing (QS) systems play important roles in regulating many physiological functions of microorganisms, such as biofilm formation, bioluminescence, and antibiotic production. One marine algicidal bacterium, Ponticoccus sp. PD-2, was isolated from the microalga Prorocentrum donghaiense, and its N-acyl-homoserine lactone (AHL)-mediated QS system was verified. In this study, we analyzed the AHLs profile of strain PD-2. Two AHLs, 3-oxo-C8-HSL and 3-oxo-C10-HSL, were detected using a biosensor overlay assay and GC-MS methods. Two complete AHL-QS systems (designated zlaI/ R and zlbI/ R) were identified in the genome of strain PD-2. When expressed in Escherichia coli, both zlaI and zlbI genes could each produce 3-oxo-C8-HSL and 3-oxo-C10-HSL. Algicidal activity was investigated by evaluating the inhibitory rate (IR) of microalgae growth by measuring the fluorescence of viable cells. We found that the metabolites of strain PD-2 had algicidal activity against its host P. donghaiense (IR 84.81%) and two other red tide microalgae, Phaeocystis globosa (IR 78.91%) and Alexandrium tamarense (IR 67.14%). β-cyclodextrin which binds to AHLs and inhibits the QS system reduced the algicidal activity more than 50%. This indicates that inhibiting the QS system may affect the algicidal metabolites production of strain PD-2. Our study indicated that a QS-regulated algicidal system may play a potential role in the process of red tides disintegration. QS might be a potential way to control red tides. [ABSTRACT FROM AUTHOR] more...

Marine biofouling has detrimental effects on the environment and economy, and current antifouling coatings research is aimed at environmentally benign, non-toxic materials. The possibility of using contact-active coatings is explored, by considering the antialgal activity of cationic poly(2-(dimethylamino)ethyl methacrylate) (PDMAEMA) brushes. The antialgal activity was investigatedviazoospore settlement and sporeling growth assays of the marine algaeUlva linzaandU. lactuca. The assay results for PDMAEMA brushes were compared to those for anionic and neutral surfaces. It was found that only PDMAEMA could disrupt zoospores that come into contact with it, and that it also inhibits the subsequent growth of normally settled spores. Based on the spore membrane properties, and characterization of the PDMAEMA brushes over a wide pH range, it is hypothesized that the algicidal mechanisms are similar to the bactericidal mechanisms of cationic polymers, and that further development could lead to successful contact-active antialgal coatings. [ABSTRACT FROM PUBLISHER] more...

Harmful algal blooms (HABs) often cause great damage to the fish aquaculture industry in the western part of Japan. Bacteria that effectively kill such phytoplankton are found in coastal seawater and are considered to influence the occurrence of HABs. Algicidal bacteria are found in abundance in seagrass beds; however, the distribution of particular bacterial strains has not yet been clarified. In this study, we determined the abundance of three algicidal Alteromonas sp. strains that were isolated as Chattonella antiqua-killing bacteria in seagrass beds and their surrounding areas in summers of 2013-2015. The strains were detected using a quantitative polymerase chain reaction (qPCR) amplification method. Two of the three algicidal bacterial strains were remarkably abundant in the seawater of an enclosed seagrass bed compared to the surrounding areas. In addition, the abundance of the three algicidal bacteria decreased when the eelgrass withered in late summer. These results suggest that growth of these algicidal bacteria was stimulated by eelgrass. The bacterial abundance estimated by qPCR was much greater than that determined by the culture-dependent method in June 2015 when the eelgrass grew thickly. This implies that the qPCR assay could be a sensitive tool to evaluate algicidal bacteria in natural environments. [ABSTRACT FROM AUTHOR] more...

Microcystis aeruginosa is a cyanobacterial bloom-causing species and is considered a serious threat to human health and biological safety. In this study, the algicidal bacterium h10 showed high algicidal effects on M. aeruginosa 7820, and strain h10 was confirmed to belong to the genus Exiguobacterium, for which the name Exiguobacterium sp. h10 is proposed. Algicidal activity and mode analysis revealed that the supernatant, rather than the bacterial cells, was responsible for the algicidal activity, indicating that the algicidal mode of strain h10 is by indirect attack through the production of algicidal substances. Analysis of the algicidal substance characteristics showed a molecular weight of <1000 Da and that algicidal substances exhibit high thermal stability and pH instability, and the characteristic functional groups of the algicidal substance mainly included carbonyl, amino and hydroxyl groups. Under the effects of the algicidal substance, the cellular pigment content was significantly decreased, and the algal cell structure and morphology were seriously damaged. The results indicate that the algicidal bacterium Exiguobacterium sp. h10 could be a potential bio-agent for controlling cyanobacterial blooms of M. aeruginosa. Significance and Impact of the Study In this study, the effects of algicidal substances from an algicidal bacterium Exiguobacterium sp. h10 on the toxic cyanobacterium, Microcystis aeruginosa 7820, were first investigated. The algicidal mode of action was confirmed as an indirect attack through the production of algicidal substances. The characteristics of the algicidal substance were determined, especially the functional groups analysis that confirmed the algicidal substances were glycolipid mixtures. With the stress of algicidal substances, the algal chlorophyll a synthesis, cell structure and morphology were seriously damaged. This study proved that algicidal bacteria are promising sources of potential cyanobacterial bloom-control, and provided good procedures for the identification and analysis of an algicidal bacterium and substances. [ABSTRACT FROM AUTHOR] more...

The Microcystis sample was selected from natural bloom water, then the algicidal effects of the bacterial strain fluid of the two algicidal bacteria, supernatant and bacterial liquid were studied. Moreover, the changes of microalgae colony and morphology in the process of algae-lysing were observed using neutral red staining and scanning electron microscope. It showed that AA06 bacteria had certain algicidal effect while AA10 bacteria had no effect. All the supernatants of the two bacterial strains had obvious algicidal effects, and the algicidal effects between the bacterial liquid and supernatant had no significant differences (P <0.05). The effects of algae-lysing mainly owed to the chemical substances secreted by algicidal bacteria. During the algae-lysing process, the algae colony did not disperse into individual cells. The segments of the dead cells still aggregated together. [ABSTRACT FROM AUTHOR] more...

Measures for removal of toxic harmful algal blooms often cause lysis of algal cells and release of microcystins (MCs). In this study, Acinetobacter sp. CMDB-2 that exhibits distinct algal lysing activity and MCs degradation capability was isolated. The physiological response and morphological characteristics of toxin-producing Microcystis aeruginosa, the dynamics of intra- and extracellular MC-LR concentration were studied in an algal/bacterial cocultured system. The results demonstrated that Acinetobacter sp. CMDB-2 caused thorough decomposition of algal cells and impairment of photosynthesis within 24 h. Enhanced algal lysis and MC-LR release appeared with increasing bacterial density from 1 × 10³ to 1 × 107 cells/mL; however, the MC-LR was reduced by nearly 94% within 14 h irrespective of bacterial density. Measurement of extracellular and intracellular MC-LR revealed that the toxin was decreased by 92% in bacterial cell incubated systems relative to control and bacterial cell-free filtrate systems. The results confirmed that the bacterial metabolite caused 92% lysis of Microcystis aeruginosa cells, whereas the bacterial cells were responsible for approximately 91% reduction of MC-LR. The joint efforts of the bacterium and its metabolite accomplished the sustainable removal of algae and MC-LR. This is the first report of a single bacterial strain that achieves these dual actions. [ABSTRACT FROM AUTHOR] more...

Palmitoleic acid (PA) is an effective algicide against the toxin-producing dinoflagellate Alexandrium tamarense ; however, its effects on the immune system of the edible bay scallop Argopecten irradians are unclear. Therefore, we investigated the effects of PA on the immune response in A. irradians by assessing total haemocyte counts (THC), alkaline phosphatase activity (ALP), nitrite oxide (NO), glutathione (GSH), and lactate dehydrogenase (LDH) levels, as well as the expression of immune-related genes ( FREP , PGRP , HSP90 , MnSOD , and Cu/ZnSOD ) at various hours post-exposure (hpe) to the compound. THC decreased in PA-treated groups, whereas ALP increased significantly in all of the PA treatment groups at 3 hpe, after which it significantly decreased. The LDH and NO levels were significantly enhanced in the high and medium concentration group. Notably, the GSH level increased in all PA treatment groups at each time interval. Our study revealed that after treatment with different concentrations of PA, variable effects on the expression of genes involved in the immune system response were observed. The results of our study demonstrate that immersing scallops in PA at effective concentrations could result in differential effects on immune system responses and expression of immune-related genes. Specifically, PA may disrupt the endocrine system or affect signal transduction pathways in the scallops. Therefore, the present study highlights the potential risk of using the PA as an algicide to control algal bloom outbreaks in the marine environment. [ABSTRACT FROM AUTHOR] more...

A coated copper sulfate algicide designed for controlled release of copper was evaluated for its effectiveness in controlling phytoplankton in hybrid catfish, ♀ Ictalurus punctatus × ♂ Ictalurus furcatus, ponds. Copper concentrations were greater in ponds receiving weekly treatments with copper sulfate crystals than in ponds in which the coated copper sulfate was suspended in porous bags and left in ponds during the study. However, the coated copper sulfate treatment provided a similar degree of phytoplankton control for a period of about 4 mo. Copper additions did not negatively affect catfish survival, production, or feed conversion in either the copper sulfate crystal treatment or in the coated copper sulfate treatment as compared with the control ( P > 0.05). Flavor scores for fish did not differ between control and treatments ( P > 0.05). The coated copper sulfate appeared to be a potentially effective method for controlling phytoplankton in aquaculture ponds. It would be easier to apply and require fewer applications, and the coated copper algicide would not present a fish toxicity issue that can arise from high copper concentration immediately following copper sulfate crystal treatment. [ABSTRACT FROM AUTHOR] more...

Prodigiosin (PG) is a bioactive compound produced by several bacterial species. Currently, many technologies are being developed for the production of PG by fermentation processes. However, new challenges are being faced with regard to the production of PG in terms of the recovery and purification steps, owing to the labile nature of PG molecules and the cost of the purification steps. Conventional methods have limitations due to high cost, low reusability, and health hazards. Hence, the present investigation was focused on the development of surface-functionalized magnetic iron oxide ([Fe3O4]F) for solvent-free extraction of bioactive PG from the bacterial fermented medium. Fe3O4 was functionalized with diethanolamine and characterized by FT-IR, diffuse reflectance spectroscopy, thermogravimetric analysis, scanning electron microscopy, and confocal microscopy. The various process parameters, such as contact time, temperature, pH, and mass of Fe3O4, were optimized for the extraction of PG using functionalized Fe3O4. Instrumental analyses confirmed that the PG molecules were cross-linked with functional groups on [Fe3O4]F through van der Waals forces of attraction. PG extracted through Fe3O4 or [Fe3O4]F was separated from the fermentation medium by applying an external electromagnetic field and regenerated for successive reuse cycles. The purity of the extracted PG was characterized by high-performance liquid chromatography, FT-IR, and UV-visible spectroscopy. The iron oxide-diethanolamine-PG cross-linked ([Fe3O4]F-PG) composite matrix effectively deactivates harmful fouling by cyanobacterial growth in water-treatment plants. The present investigation provides the possibility of solvent-free extraction of bacterial bioactive PG from a fermented medium using functionalized magnetic iron oxide. [ABSTRACT FROM AUTHOR] more...

Copper sulfate (CuSO4) has been widely used as an algicide to control harmful cyanobacterial blooms (CyanoHABs) in freshwater lakes. However, there are increasing concerns about this application, due mainly to the general toxicity of CuSO4 to other aquatic species and its long-term persistence in the environment. This study reported the isolation and characterization of two natural algicidal compounds, i.e., tryptamine and tryptoline, from Streptomyces eurocidicus JXJ-0089. At a concentration of 5 μg/ml, both compounds showed higher algicidal efficiencies than CuSO4 on Microcystis sp. FACHB-905 and some other harmful cyanobacterial strains. Tryptamine and tryptoline treatments induced a degradation of chlorophyll and cell walls of cyanobacteria. These two compounds also significantly increased the intracellular oxidant content, i.e., superoxide anion radical (O2-) and malondialdehyde (MDA), but reduced the activity of intracellular reductants, i.e., superoxide dismutase (SOD), of cyanobacteria. Moreover, tryptamine and tryptoline treatments significantly altered the internal and external contents of microcystin-LR (MC-LR), a common cyanotoxin. Like CuSO4, tryptamine and tryptoline led to releases of intracellular MC-LR from Microcystis, but with lower rates than CuSO4. Tryptamine and tryptoline (5 μg/ml) in cyanobacterial cultures were completely degraded within 8 days, while CuSO4 persisted for months. Overall, our results suggest that tryptamine and tryptoline could potentially serve as more efficient and environmentally friendly alternative algicides than CuSO4 in controlling harmful cyanobacterial blooms. [ABSTRACT FROM AUTHOR] more...

To help ban the use of general toxic algicides, research efforts are now directed towards the discovery of compounds that are specifically acting as cyanocides. Here, we review the past and look forward into the future, where the less desirable general algicides like copper sulphate, diuron or endothall may become replaced by compounds that show better specificity for cyanobacteria and are biodegradable or transform into non-toxic products after application. For a range of products, we review the activity, the mode of action, effectiveness, durability, toxicity towards non-target species, plus costs involved, and discuss the experience with and prospects for small water volume interventions up to the mitigation of entire lakes; we arrive at recommendations for a series of natural products and extracted organic compounds or derived synthetic homologues with promising cyanocidal properties, and briefly mention emerging nanoparticle applications. Finally, we detail on the recently introduced application of hydrogen peroxide for the selective killing of cyanobacteria in freshwater lakes. [ABSTRACT FROM AUTHOR] more...

Acinetobacter sp. J25 exhibited good denitrification and high algicidal activity against toxic Microcystis aeruginosa . Response surface methodology (RSM) experiments showed that the maximum algicidal ratio occurred under the following conditions: temperature, 30.46 °C; M. aeruginosa density, 960,000 cells mL − 1 ; and inoculum, 23.75% (v/v). Of these, inoculum produced the maximum effect. In the eutrophic landscape water experiment, 10% bacterial culture was infected with M. aeruginosa cells in the landscape water. After 24 days, the removal ratios of nitrate and chlorophyll-a were high, 100% and 87.86%, respectively. The denitrification rate was approximately 0.118 mg NO 3 − –N·L − 1 ·h − 1 . Moreover, the high-throughput sequencing result showed that Acinetobacter sp. J25 was obviously beneficial for chlorophyll-a and nitrate removal performance in the eutrophic landscape water treatment. Therefore, strain J25 is promising for the simultaneous removal of chlorophyll-a and nitrate in the eutrophic landscape water treatment. [ABSTRACT FROM AUTHOR] more...

The aim of the present study was to obtain a marine bacterium active against Karenia mikimotoi from the East China Sea and to characterize its extracellular algicidal substances. Using preparative high-performance liquid chromatography (prep-HPLC) and electrospray ionization/quadrupole-time of flight mass spectrometer coupled with a high-performance liquid chromatography (LC/MS-Q-TOF) system, we purified the alga-lysing substance produced by strain ZR-2 and determined its molecular structure. Based on morphology and l6S ribosomal DNA (rDNA) sequence analysis, the ZR-2 strain was highly homologous to Thalassospira species. Algicidal activity against K. mikimotoi was detected in the cell-free filtrate but not in bacterial cells. The alga-lysing substance produced by ZR-2 was ethanol-soluble and thermostable, with a retention time of 6.3 min and a measured elemental composition of CHO ([M-H] ion at m/ z 121.0295). The alga-lysing substance produced by ZR-2 was determined to be benzoic acid. Compared with the negative control, both purified ZR-2 bacteria-free filtrate and standard benzoic acid promoted K. mikimotoi cell disruption and induced K. mikimotoi cell content leakage. Our study is the first to report benzoic acid activity against K. mikimotoi as well as production of benzoic acid by a Thalassospira species. [ABSTRACT FROM AUTHOR] more...

In the present study, we synthesized 65 dichlorobenzylamine derivatives and investigated their algicidal activity against harmful red tides. The 3,4-dichlorobenzylamine derivatives showed relatively high activity against Cochlodinium polykrikoides, Heterosigma akashiwo, Chattonella marina, and Heterocapsa circularisquama, and the synthesized compounds 27, 28, 33, 34, 35, and 36 showed the highest algicidal activity after 24 h at 0.1 ~ 1.0 μM LC against the four harmful algae species. To verify the safety of the compounds, acute ecotoxicology tests using the water flea ( Daphnia magna) and zebrafish ( Danio rerio) were conducted, and the tests confirmed that compounds 33 and 34 were not harmful because the target organisms showed high survival rates at 15 μM. The results indicate that compounds 33 and 34 are suitable substances for use in controlling harmful algae species. [ABSTRACT FROM AUTHOR] more...

Proliferation of cyanobacteria in aquatic ecosystems has caused water security problems throughout the world. Our preliminary study has showed that Pseudomonas aeruginosa can inhibit the growth of cyanobacterium, Microcystis aeruginosa . In order to explore the inhibitory mechanism of P. aeruginosa on the cell growth and synthesis of intracellular substances of M. aeruginosa , concentrations of Chlorophyll-a, intracellular protein, carbohydrate, enzyme activities and ion metabolism of M. aeruginosa , were investigated. The results indicated that 83.84% algicidal efficiency of P. aeruginosa was achieved after treatment for 7 days. The strain inhibited the reproduction of M. aeruginosa by impeding the synthesis of intracellular protein and carbohydrate of cyanobacterium, and only a very small part of intracellular protein and carbohydrate was detected after exposure to P. aeruginosa for 5 days. P. aeruginosa caused the alteration of intracellular antioxidant enzyme activity of M. aeruginosa , such as catalase, peroxidase. The accumulation of malondialdehyde aggravated membrane injury after treatment for 3 days. P. aeruginosa also affected the ion metabolism of cyanobacteria. The release of Na + and Cl − was significantly enhanced while the uptake of K + , Ca 2+ , Mg 2+ , NO 3 − and SO 4 2 − decreased. Surface morphology and intracellular structure of cyanobacteria and bacterial cells changed dramatically over time as evidenced by electron microscope (SEM) and transmission electron microscope (TEM) analysis. These results revealed that the algicidal activity of P. aeruginosa was primarily due to the fermentation liquid of P. aeruginosa that impeded the synthesis of intracellular protein and carbohydrate, and damaged the cell membrane through membrane lipid peroxidation. [ABSTRACT FROM AUTHOR] more...

Objectives: To biochemically characterize synthetic peptides to control harmful algal blooms (HABs) that cause red tides in marine water ecosystems. Results: We present an analysis of several short synthetic peptides and their efficacy as algicidal agents. By altering the amino acid composition of the peptides we addressed the mode of algicidal action and determine the optimal balance of cationic and hydrophobic content for killing. In a controlled setting, these synthetic peptides disrupted both plasma and chloroplast membranes of several species known to result in HABs. This disruption was a direct result of the hydrophobic and cationic content of the peptide. Furthermore, by using an anti-HAB bioassay in scallops, we determined that these peptides were algicidal without being cytotoxic to other marine organisms. Conclusions: These synthetic peptides may prove promising for general marine ecosystem remediation where HABs have become widespread and resulted in serious economic loss. [ABSTRACT FROM AUTHOR] more...

Controlling eutrophication with algicidal bacteria is widely recognized as an effective solution. Here, an integrated transcriptomic and metabolomic approach was used to elucidate the algicidal process of Enterobacter hormaechei F2, which exhibits substantial algicidal activity. At the transcriptome level, RNA sequencing (RNA-seq) identified 1104 differentially expressed genes in the algicidal process of the strain, thus indicating that amino acids, energy metabolism, and signaling-related genes were significantly activated during the algicidal process according to the Kyoto Encyclopedia of Genes and Genomes enrichment analysis. By analyzing the enriched amino acid and energy metabolism pathways using metabolomics, we identified 38 upregulated and 255 downregulated significantly changed metabolites in the algicidal process and an accumulation of B vitamins, peptides, and energy substances. The integrated analysis demonstrated that energy and amino acid metabolism, co-enzymes and vitamins, and bacterial chemotaxis are the most important pathways for the algicidal process of this strain, and metabolites from these pathways, such as thiomethyladenosine, isopentenyl diphosphate, hypoxanthine, xanthine, nicotinamide, and thiamine, all exhibited algicidal activity. • Algicidal activity of E. hormaechei F2 was investigated. • Energy metabolism- and aromatic amino acid metabolism-related pathways are involved in algicidal process. • Peptides, co-enzymes, vitamins, and energy substances are related to algicidal activity. • Thiomethyladenosine, isopentenyl diphosphate, hypoxanthine, xanthine, thiamine, and nicotinamide may relate to algicidal activity. [ABSTRACT FROM AUTHOR] more...

Microcystin release from algal cells influences use of copper-algaecides in water resources. Accurate data regarding relationships between copper-algaecide exposures and responses of microcystin-producing algae are needed to make informed management decisions. Responses of Microcystis aeruginosa were measured in terms of cellular microcystin-LR (MC-LR), aqueous MC-LR, and chlorophyll- a following exposure to CuSO 4 and copper-ethanolamine. Comparisons were made between treated and untreated samples, and copper formulations. EC 50 s and slopes for M. aeruginosa responses to copper exposures were calculated. Algal responses followed a sigmoidal exposure-response relationship, and cellular MC-LR and chlorophyll- a were negatively related to copper concentrations. Aqueous MC-LR increased with copper concentrations, although the increase in aqueous MC-LR was not proportional to decreases in cellular MC-LR and chlorophyll- a . Cellular MC-LR and chlorophyll a declined at a greater rate than aqueous MC-LR increased. Total MC-LR was less than untreated controls following copper exposure. Differences were measured between copper formulations in terms of aqueous and total MC-LR concentrations at concentrations of 0.5 and 1.0 mg Cu L-1. Aqueous and total MC-LR were greater (10–20%) following exposure to CuSO 4 compared to copper-ethanolamine one day following exposure. The positive relationship between copper concentration and aqueous MC-LR at 0.07–1.0 mg Cu L-1 demonstrates that lower copper concentrations were as effective as higher concentrations in controlling M. aeruginosa while decreasing the total amount of MC-LR, and minimizing the proportion of MC-LR released to the aqueous-phase. Results serve to support more accurate risk evaluations of MC-LR concentrations when M. aeruginosa is exposed to copper-algaecides and when it is untreated. [ABSTRACT FROM AUTHOR] more...

Copper-based algaecides are used to control algae that compromise uses of lakes and reservoirs. However, there are concerns regarding potential adverse effects to benthic macroinvertebrates following long-term, repeated applications. Multiple lines-of-evidence are useful for evaluating potential ecological risks. These lines-of-evidence are encompassed in the sediment quality triad (SQT) and include sediment copper concentrations, in situ benthic invertebrate abundance, and sediment toxicity testing. The objective of this study was to measure potential ecological risks associated with long-term applications of copper algaecides in coves in Lay Lake, Alabama. Sediments from three coves treated for 7, 10, and 20 years were compared to sediments from three untreated coves in terms of copper concentrations, in situ benthic macroinvertebrate total abundance, and survival of Hyalella azteca and Chironomus dilutus in laboratory sediment toxicity tests. Sediment copper concentrations were not different between treated and untreated coves, with the exception of one treated cove (PC-1S) that contained elevated sediment copper concentrations compared to all other coves. However, the copper was not bioavailable to organisms based on in situ macroinvertebrate abundance and laboratory toxicity tests. In situ benthic invertebrate abundance was not different between treated and untreated coves. In all sediments tested, there were no measurable adverse effects to H. azteca and there were no significant differences in survival of C. dilutus between treated and untreated coves. Based on the weight-of-evidence approach utilized in this study, long-term copper use in three Lay Lake coves has not resulted in adverse effects to benthic invertebrates compared to untreated coves. [ABSTRACT FROM AUTHOR] more...

Aim: Bacteria associated with harmful algal blooms can play a crucial role in regulating algal blooms in the environment. This study aimed at isolating and identifying algicidal bacteria in Dinoflagellate culture and to determine the optimum growth requirement of the algicidal bacteria, Loktanella sp. Gb-03. Materials and Methods: The Dinoflagellate culture used in this study was supplied by Professor Gires Usup's Laboratory, School of Environmental and Natural Resources Sciences, Faculty of Science and Technology, University Kebangsaan Malaysia, Malaysia. The culture was used for the isolation of Loktanella sp., using biochemical tests, API 20 ONE kits. The fatty acid content of the isolates and the algicidal activity were further evaluated, and the phenotype was determined through the phylogenetic tree. Results: Gram-negative, non-motile, non-spore-forming, short rod-shaped, aerobic bacteria (Gb01, Gb02, Gb03, Gb04, Gb05, and Gb06) were isolated from the Dinoflagellate culture. The colonies were pink in color, convex with a smooth surface and entire edge. The optimum growth temperature for the Loktanella sp. Gb03 isolate was determined to be 30°C, in 1% of NaCl and pH7. Phylogenetic analysis based on 16S rRNA gene sequences showed that the bacterium belonged to the genus Loktanella of the class Alphaproteobacteria and formed a tight cluster with the type strain of Loktanella pyoseonensis (97.0% sequence similarity). Conclusion: On the basis of phenotypic, phylogenetic data and genetic distinctiveness, strain Gb-03, were placed in the genus Loktanella as the type strain of species. Moreover, it has algicidal activity against seven toxic Dinoflagellate. The algicidal property of the isolated Loktanella is vital, especially where biological control is needed to mitigate algal bloom or targeted Dinoflagellates. [ABSTRACT FROM AUTHOR] more...

Algicidal bacteria offer a promising option for killing cyanobacteria. In this study, a newly isolated strain of Bacillus methylotrophicus , ZJU, was used to control Microcystis aeruginosa . Analyses of relative reactive oxygen level, malondialdehyde content, superoxide dismutase activity, and fluorescence staining indicated that oxidative damage caused by the algicidal supernatant of strain ZJU mainly affected the cell membrane and consequently the membrane permeability and membrane potential of M. aeruginosa cells. Furthermore, an embedded immobilization technique was employed to improve the practical application of strain ZJU as an algicidal agent. On this basis, we proposed a novel concept of enhancing the algicidal properties of immobilized ZJU by adding Fe 3 O 4 nanoparticles and wheat bran in the process of immobilization. Our studies showed that Fe 3 O 4 nanoparticles conferred the immobilized bacteria with a magnetization of 30.87 emu/g, and this magnetization enabled efficient re-collection of the immobilized bacteria by magnetic means. Moreover, wheat bran endowed the immobilized bacteria with 10.34% higher algicidal activity than immobilized bacteria without wheat bran. The results indicate a novel concept of enhancing the algicidal property of bacteria against M. aeruginosa by adding Fe 3 O 4 nanoparticles and wheat bran. [ABSTRACT FROM AUTHOR] more...

Background: Harmful algal blooms (HABs) caused by the dinoflagellate Cochlodinium polykrikoides lead to severe environmental impacts in oceans worldwide followed by huge economic losses. Algicide agent copper sulfate (CuSO4) is regard as an economical and effective agent for HABs mitigation; its biochemical and physiological effects were revealed in C. polykrikoides. However, molecular mechanisms of CuSO4 effect on the C. polykrikoides, even other HAB species, have not been investigated. The present study investigated the transcriptional response of C. polykrikoides against CuSO4 treatments, with the aim of providing certain molecular mechanism of CuSO4 effect on the C. polykrikoides blooms. Results: RNA-seq generated 173 million reads, which were further assembled to 191,212 contigs. 43.3 %, 33.9 %, and 15.6 % of contigs were annotated with NCBI NR, GO, and KEGG database, respectively. Transcriptomic analysis revealed 20.6 % differential expressed contigs, which grouped into 8 clusters according to K-means clustering analysis, responding to CuSO4; 848 contigs were up-regulated and 746 contigs were down-regulated more than 2-fold changes from 12 h to 48 h exposure. KEGG pathway analysis of eukaryotic homologous genes revealed the differentially expressed genes (DEGs) were involved in diverse pathway; amongst, the genes involved in the translation, spliceosome, and/or signal transduction genes were highly regulated. Most of photosystem related genes were down-regulated and most of mitochondria related genes were up-regulated. In addition, the genes involved in the copper ion binding or transporting and antioxidant systems were identified. Measurement of chlorophyll fluorescence showed that photosynthesis was significantly inhibited by CuSO4 exposure. Conclusions: This study reported the first transcriptome of the C. polykrikoides. The widely differential expressed photosystem genes suggested photosynthetic machinery were severely affected, and may further contribute to the cell death. Furthermore, gene translation and transcription processes may be disrupted, inhibiting cell growth and proliferation, and possibly accelerating cell death. However, antioxidant systems resistant to CuSO4 caused stress; mitochondrion may compensate for photosynthesis efficiency decreasing caused energy deficiency. In addition, various signal transduction pathways may be involved in the CuSO4 induced regulation network in the C. polykrikoides. These data provide the potential transcriptomic mechanism to explain the algicide CuSO4 effect on the harmful dinoflagellate C. polykrikoides. [ABSTRACT FROM AUTHOR] more...