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Monitoring toxigenic cyanobacteria in freshwaters is of great importance due to the adverse health impacts on humans and aquatic organisms. Here we studied cyanobacterial occurrence and biodiversity in a drinking water reservoir in Tehran province, Iran. In total, nine different species representing three orders of Synechococcales, Oscillatoriales and Nostocales were isolated and classified into six families and seven genera ranging from 92.3% to 99.0% similarities in their partial 16S rDNA with GenBank sequences. The cultures were analyzed for cyanotoxins production by the Artemia salina bioassay, ultrahigh performance liquid chromatography-tandem mass spectrometry (UPLC-MS/MS) and also screened for the presence of marker genes involved in toxins production. Ethyl acetate extracts of three strains showed more than 50% mortality on A. salina larvae after 24 h at a concentration of 500 µg/ml. Production of at least one of the cyanotoxins, microcystin (MC), cylindrospermopsin (CYN) and anatoxin-a (ATX-a), was detected in 6 of the strains. Seven MC variants with a total concentration of 130.6 ng/mg of biomass dry weight were detected for the strain Phormidium sp. UTMC6001 and molecular screening of the mcyE gene also confirmed the presence of this biomarker in its genome. Our study also revealed the production of CYN in a novel picocyanobacterial strain Cyanobium sp. UTMC6007 at 1.0 ng/mg of biomass dry weight. Considering the limited information on freshwater toxic cyanobacteria taxonomy in the Middle East, these findings will expand our knowledge and consequently aid in development of new water management policies in future.

Picocyanobacteria are small cyanobacteria, being about 0.8–1.5 µm in size. They are present in freshwater environments all over the world and are known to cause harmful algal blooms, although their effects are not well understood. Algal blooms are important to manage because they threaten freshwater resources, with potentially severe effects on ecological and human health. There is also increased urgency due to urbanization and climate change trends which are expected to exacerbate these bloom dynamics. These changes are expected to especially favour picocyanobacteria groups, emphasizing the need for better characterization of their effects in the environment. In this study, we report the discovery that Synechococcus sp. could produce cylindrospermopsin (CYN) and anatoxin-a (ATX). This ability had never been previously reported for this species. Their toxin genes were also partial compared to other major producers such as Raphidiopsis sp. and Anabaena sp., demonstrating potentially unique synthesis pathways that provides insight into the various mechanisms of genetic variation that drives toxin synthesis. The Synechococcus sp. strains were found to produce about 9.0 × 10−5–6.8 × 10−4 fg CYN cell−1 and 4.7 × 10−4–1.5 × 10−2 fg ATX cell−1. The potential for Synechococcus sp. to be toxic highlights a global concern due to its widespread distribution, and through environmental trends that increasingly favour its productivity within freshwater systems around the world.

Although the use of Sulfluramid (N-ethyl perfluorooctane sulfonamide (N-EtFOSA)) has been restricted by the Stockholm Convention, it is still frequently detected in the environmental matrices and in use in some countries. Employing constructed wetlands as treatment systems requires understanding of the biodegradation process in the rhizosphere and the effect of contaminants on the microbes of wetlands. This study aimed to investigate the interactions between the microbial community and N-EtFOSA under aerobic and anaerobic conditions. Aerobic biotransformation of N-EtFOSA occurred with a half-life of 0.51 day and yielded 85.1 mol% PFOS of after 91 days. Kinetic modelling revealed that cleavage of the S N was the rate-limiting degradation step. Biotransformation was not observed under anaerobic and anoxic conditions, suggesting that N-EtFOSA is recalcitrant to biodegradation without dissolved oxygen. Under aerobic condition, the presence of N-EtFOSA and its biotransformation products decreased the microbial richness and diversity and exerted selective pressure on the microbial community. Enrichment of Methylocaldum was significant (49%) in the presence of N-EtFOSA compared to unexposed conditions (11%), suggesting that Methylocaldum is relatively tolerant to N-EtFOSA and potentially degrading N-EtFOSA. Under anaerobic conditions, the microbial richness and diversity were not significantly altered by the presence of N-EtFOSA. Only Methanomethylovorans increased significantly in the spiked microcosm (30% vs. 20%). These findings provide knowledge for comprehending the contribution of N-EtFOSA to other PFASs in various environmental conditions, information about microbial community changes in response to PFASs and robust microbial species which can degrade N-EtFOSA in the environment.

The increased antibiotic pollutants in aquatic environments pose severe threats on microbial ecology due to their extensive distribution and antibacterial properties. A total of 16 antibiotics including fluoroquinolones (FQs) (ofloxacin (OFX), ciprofloxacin (CFX), norfloxacin (NFX)), Sulfonamides (SAs) (sulfamonomethoxine (SMM), sulfadiazine (SDZ), sulfaquinoxaline (SQX)), Tetracyclines (TCs) (tetracycline (TC), doxycycline (DC)), β-lactams (penicillin G (PEN G), penicillin V (PEN V), cefalexin (LEX)), Macrolides (MLs) (erythromycin-H2O (ETM), tylosin (TYL)) and other antibiotics (Polymix-B (POL), Vancomycin (VAN), Lincomycin (LIN)) were detected in the surface water of the Qingcaosha Reservoir. Multivariate statistical analysis indicated that both water quality and physicochemical indexes have less contributions on variations of these antibiotics, suggesting the concentrations of antibiotics inside the reservoir are mainly affected by upstream runoff and anthropic activity along the river. Antibiotics including TYL, PEN G and ETM showed significant correlations with variations of bacterial community composition, and closely connected with various gram-negative bacteria in co-occurrence/exclusion patterns of the network, suggesting these bacterial taxa play important roles in the course of migration and transformation of related antibiotics. In conclusion, further research is required to evaluate the potential risk of genetic transfer of resistance to related bacteria induced by long-term exposure to low levels of antibiotics in the environment.

The feasibility of cyanobacteria removal from freshwater by a dielectric barrier discharge (DBD) process is investigated. Seven commercial and environmental cyanobacteria strains, as well as real algae-laden water, were tested. The removal of the cyanobacteria was evaluated by analyzing the changes in chlorophyll a content, total organic carbon (TOC) concentration, and cell morphology. Nearly total removal of chlorophyll a was achieved within 20 min, while the TOC analysis exhibited an increase-decrease-increase trend in 60 min of treatment, likely due to the oxidation of intracellular and intercellular materials. Observation under light microscopy revealed the disruption of intracellular and intercellular structures within 5 min of DBD treatment and thus supported the TOC analysis. Increasing the salinity of the medium from 0 to 5 parts per thousand (ppt) improved treatment efficiency, where similar level of chlorophyll a removal (around 93%) was achieved in only half the treatment time. Application of DBD on real algae-laden water from a fish farm yielded higher treatment efficiency than in synthetic medium, indicating the promising application of DBD as a means to control cyanobacteria bloom in fresh and estuary water bodies.

Planktothricoides is a free-living filamentous cyanobacterium belonging to the order Oscillatoriales and the family Phormidiaceae, capable of forming bloom in fresh and brackish waters. A unicyanobacterial non-axenic culture dominated by Planktothricoides sp. SR001 was obtained from a freshwater reservoir in Singapore. The draft genome presented here is the first tropical freshwater Planktothricoides sp. ever sequenced. The genome of 7.0Mbp contains 5,776 genes predicted using the JGI IMG pipeline. The whole genome sequence allows identification of genes encoding for nitrogen-fixation, accessory photosynthetic pigments and biosynthesis of an off-flavor compound, 2-methylisoborneol, which has been experimentally verified here based on metabolite detection. In addition, strain SR001 genome contains an operon putatively involved in the production of a linear tripeptide cyanobactin related to viridisamide A and aeruginosamide, with the later known to possess anti-microbial or cytotoxic effect.

Cylindrospermopsis is known to be one of the major bloom-forming cyanobacterial genera in many freshwater environments. We report here the draft genome sequence of a tropical Cylindrospermopsis sp. strain, CR12, which is capable of producing the hepatotoxic cylindrospermopsin.

The temporal variations in cyanobacteria and microcystin production in a tropical reservoir, Kranji Reservoir in Singapore, were studied from February 2008 to August 2009 by using molecular techniques and enzyme-linked immunosorbent assay (ELISA) respectively. Results from PCR and qPCR showed that Microcystis and Anabaena were present (mean concentrations 4.16 × 10 6 gene copies/mL and 4.47 × 10 4 gene copies/mL respectively) and were well correlated to each other ( P Microcystis was the primary microcystin producer. The average percentage of toxigenic Microcystis spp. was 55.92%, whereas no Anabaena -specific microcystin producing gene was detected. Microcystis -specific microcystin-producing genes mcyB and mcyD were detected in all the samples, together with dominant detection of mcyA and mcyE genes. However, a low positive detection rate was observed for mcyC . Due to the combined effects of high temperature, light and nutrient conditions in this tropical reservoir, the Microcystis cell concentrations were higher and more uniform compared to other Microcystis blooms reported in subtropical and temperate regions. Furthermore, the proportion of toxigenic Microcystis in the total Microcystis population was considerably higher. Principle component analysis and multiple linear regression analysis showed that total nitrogen and total phosphorus were positively correlated with the abundances of total Microcystis and toxigenic Microcystis . In addition, total nitrogen, pH and dissolved oxygen were positively correlated with the microcystin concentration.

The increasing occurrence of harmful cyanobacterial blooms, often linked to deteriorated water quality and adverse public health effects, has become a worldwide concern in recent decades. The use of molecular techniques such as real-time quantitative PCR (qPCR) has become increasingly popular in the detection and monitoring of harmful cyanobacterial species. Multiplex qPCR assays that quantify several toxigenic cyanobacterial species have been established previously; however, there is no molecular assay that detects several bloom-forming species simultaneously. Microcystis and Cylindrospermopsis are the two most commonly found genera and are known to be able to produce microcystin and cylindrospermopsin hepatotoxins. In this study, we designed primers and probes which enable quantification of these genera based on the RNA polymerase C1 gene for Cylindrospermopsis species and the c-phycocyanin beta subunit-like gene for Microcystis species. Duplex assays were developed for two molecular techniques—qPCR and droplet digital PCR (ddPCR). After optimization, both qPCR and ddPCR assays have high linearity and quantitative correlations for standards. Comparisons of the two techniques showed that qPCR has higher sensitivity, a wider linear dynamic range, and shorter analysis time and that it was more cost-effective, making it a suitable method for initial screening. However, the ddPCR approach has lower variability and was able to handle the PCR inhibition and competitive effects found in duplex assays, thus providing more precise and accurate analysis for bloom samples.