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Frequent harmful cyanobacteria blooms limit the sustainable development of aquaculture. Algicidal bacteria can efficiently control harmful algae without secondary pollution. The algicidal bacteria CZBC1 can lyse Oscillatoria spp. and other harmful cyanobacteria, but its effector mechanism and algicidal threshold are unknown. In this study, we examined the algicidal effect of CZBC1 on O. chlorina, O. tenuis, and O. planctonica by microscopic enumeration and scanning electron microscopy observation. Then, we examined the alginolytic effects of CZBC1 (concentrations 103–106 colony forming units (cfu)/mL) on these three species (concentrations 103–106 cells/mL) to determine the effective concentrations of CZBC1 for Oscillatoria spp. alginolysis. Results showed that CZBC1 can directly lyse O. chlorina and O. tenuis but indirectly lyse O. planctonica. When the initial concentration of CZBC1 was 106 cfu/mL, alginolytic effects were high for all three species at all concentrations, and the alginolytic rate could reach 100% in 3–9 days. When the initial concentration of CZBC1 was lower (103 cfu/mL), its inhibitory effects were delayed by 2–5 days, but the cell counts were significantly decreased compared with the control, evidencing significant alginolysis. In addition, the higher the concentration of the algicidal bacteria suspension, the more significant the alginolytic effects. Our results indicate that CZBC1 has different alginolytic mechanisms for O. chlorina, O. tenuis, and O. planctonica, and that different initial concentrations of CZBC1 have different alginolytic effects on these algal species.

Algicidal bacteria may play a role in controlling algal blooms. Previously, a Bacillus cereus strain (CZBC1) was shown to have specificity against harmful Cyanophyta. To elucidate the characteristics of microalgal and bacterial communities in shrimp culture associated with the algicidal bacterium CZBC1 and its combined use with the addition of organic carbon, we established a shrimp culture system in which the dominant macroalgal species were Oscillatoria chlorina (Cyanophyta) and Chlorella pyrenoidosa (Chlorophyta). We studied water-column microalgal and bacterial communities in control (GC), bacteria (GB), and bacteria-carbon (GBC) treatment groups at the mid-point (Day 28) and end (Day 56) of the experiment. The algicidal bacterium CZBC1 was able to regulate abundance of Cyanophyta on Days 28 and 56 in GB and GBC. Abundances of Cyanophyta on Days 28 and 56 ) in GB (

Although the distribution of progestagens in aquatic environments has been widely reported, details on their uptake, elimination, and biotransformation in fish have received little attention. This study investigated the uptake, elimination, and biotransformation potential of a progestagen, cyproterone acetate (CPTA), in Nile tilapia ( Oreochromis niloticus) exposed to an environmentally relevant concentration under semistatic regimes. CPTA in tilapia tissues followed a similar pattern, reaching a concentration plateau within 4 days of exposure, and dropping to below limits of quantitation within 4 days of elimination. The calculated steady-state bioconcentration factors suggest a low bioconcentration potential of CPTA in juvenile tilapia. Results of enzymatic hydrolysis treatments revealed that no conjugates of CPTA were present in tissues, but conjugated biotransformation products of CPTA were found in bile, liver, and muscle. Most CPTA entered tissues and then was biotransformed into seven different products by phase I and phase II metabolism. The concentrations of endogenous cortisol were significantly influenced by CPTA in plasma and liver during the uptake period. These findings suggest that biotransformation products of CPTA should be considered for the assessment of the bioconcentration potential and ecological effects of progestagens.

Background: Microbiota carrying multiple antibiotic resistance genes (ARGs) and virulence factors (VFs) are posing increasing risks to public health. Particularly the rapid spread of human pathogenic bacteria (HPB) with antibiotic resistance is recognized as a top health issue. The occurrence and abundance of ARGs in aquaculture have been investigated following metagenomic approaches. However, few studies have investigated the antibiotic resistome and VFs and their HPB hosts in aquaculture. Moreover, the relationships between ARGs and VFs and their microbiome in aquaculture are poorly understood. Results: The profiles of the antibiotic resistome, VFs, and HPB in aquaculture in Southern China were investigated. In total, 492 subtypes of 24 ARGs types were detected. Multidrug ARGs were most predominant, followed by macrolide-lincosamide-streptogramin (MLS). Proteobacteria were the most predominant phylum carrying ARGs, followed by Firmicutes. Fifty-two HPB genera were detected. Firmicutes was the most abundant phylum, followed by Proteobacteria. Staphylococcus was the most abundant HPB genus. The samples contained 363 VFs, with Capsule being the most abundant. Seven HPB phyla, including 42 HPB genera, carried VFs, and the abundance of Bacillus was highest. The abundances of ARGs and VFs were highest in the sediment. However, the abundance of HPB was highest in shrimp guts and Staphylococcus was most abundant. Most ARGs were more prevalent on chromosomes than on plasmids. Source tracking analysis showed that the sediment was the greatest contributor to microbes carrying ARGs, VFs, and HPB in shrimp guts. Additionally, the water source contributed some of the HPB of shrimp guts. Conclusions: This study provides in-depth profiles of the abundances, diversity, distribution, and prevalence of ARGs, VFs, and their hosts HPB in aquaculture for the first time. Sediment was the most direct and important contributor to the ARGs, VFs, and HPB in the shrimp guts. The prevalence of HPB in aquaculture, particularly the high abundance of Staphylococcus in shrimp guts, poses potential risks to human health and food safety. Aquaculture water sources should be monitored and protected. The findings of this study provide a better understanding of the dissemination and hosts of ARGs and VFs for improving aquaculture management and public health surveillance.

Although the occurrence and distribution of antibiotics in aquatic environments and reared organisms have been widely reported, the spatiotemporal variations and sources of antibiotics throughout the rearing period of aquaculture remain unclear. In this study, the concentrations and spatiotemporal variations of antibiotics in water sources, pond water, sediment, feed, and reared shrimp samples during three rearing periods in an ecological shrimp farm in Southern China were investigated. The water, sediment, and feed samples were found to contain twelve, nine, and four types of antibiotics, respectively, and the concentration of erythromycin-H2O was the highest among these antibiotics. No target antibiotics were detected in the reared shrimp samples from this typical shrimp farm, which employed ecological rearing with no antibiotic use throughout the rearing processes. The total concentrations of antibiotics in water source were 1.96–40.58 times higher than those in pond water. A significant decrease in the total antibiotic concentrations of the pond water was observed, while a significant increase was observed in sediment during each rearing period (p

Although research regarding antibiotic resistance genes (ARGs) in aquaculture environments has gained increasing scientific interest, further studies are required to understand the abundances and removal mechanisms of ARGs during the entire rearing period of shrimp aquaculture. Thus, in this study, abundances, distributions and removal rates of ARGs in different environmental compartments of intensive shrimp farms in South China were investigated during the entire rearing period. The results indicated that sul1 and cmlA were the predominant ARGs in the water and sediment samples. Additionally, the total abundance of ARGs was higher in shrimp pond water than in the source water and farm effluent. Moreover, sediment samples indicated significantly higher ARG abundances than water samples from the shrimp ponds (P

Although the occurrence of antibiotics and antibiotic resistance genes (ARGs) in aquatic environmental has been widely reported, the distribution and variations of these emerging contaminants in the coral reef regions remain unclear. This study investigated the occurrence of these contaminants, and their spatial and seasonal variations in both coral reef regions and non-coral reef regions adjacent to two typical islands in the South China Sea. Eighteen antibiotics and seven ARGs were detected in the surface water with total concentrations ranging from 43.2 to 441 ng/L, and 2.11 × 104 to 8.00 × 106 copies/L, respectively. Erythromycin-H2O was the most dominant antibiotic in all samples. QnrD was dominant in the dry season, whereas sul1, sul2, and floR were the most abundant in the wet season, indicating obvious seasonal variations. The distribution of ARGs was mainly influenced by changes in salinity caused by anthropogenic activities in wet season.

Although the prevalence and concentrations of antibiotic resistance genes (ARGs) in aquaculture is receiving increasing scientific interest, there is little understanding of the direct sources and dissemination pathways of ARGs in marine aquaculture-reared organisms. This study investigated the dynamics of ARGs and the bacterial community throughout the rearing period in a typical marine aquaculture farm in South China. The results demonstrated that sul1 and qnrD were predominant in the sediment, and qnrD and qnrA were predominant in the intestinal tracts of shrimps. Network analysis showed that the chemical oxygen demand, total organic carbon, dissolved organic carbon, suspended solids, and total phosphorus were positively correlated with the predominant ARGs. The results of the network and source tracking analyses indicate that environmental factors and the bacterial community may drive the dissemination of ARGs dissemination in the environment and in shrimp reared by marine aquaculture, and sediment is the most direct and important medium in this dissemination. These results aid in improving our understanding of the sources, level, and dissemination of ARGs in marine aquaculture.

Ammonia is the main pollution factor of the aquatic environment in marine shrimp culture systems. In order to demonstrate the feasibility of the combination of biofloc technology and nitrifying biofilter for the ammonia removal, a 70-day production trial was conducted in a simplified pilot-scale hybrid biofloc-based recirculating aquaculture system (biofloc-RAS) with the intensive culture of Litopenaeus vannamei. Nitrogen dynamics and nitrifying microbial communities were investigated in three replicated systems simultaneously under the conditions of high feed loading and zero water exchange. Along with biofloc development in the culture tank and biofilm formation in the nitrifying biofilter during the trial, nitrification could be fastly and effectively established in the system, which was indicated by the dynamics of total ammonia nitrogen (TAN), NO2–-N, NO3–-N, and total nitrogen (TN) concentrations. Meanwhile, similar nitrifying microorganisms could be found between biofloc and biofilm, despite some differences in abundance, diversity, and composition of ammonia-oxidizing archaea and bacteria and nitrite-oxidizing bacteria. High TAN removal rate could be achieved and was significantly and positively correlated with abundances of these nitrifying microbial communities in both biofloc and biofilm, further indicating that both biofloc and biofilm could contribute highly to nitrification performance of the biofloc-RAS. The results of this study indicate a potential application of the biofloc-RAS in coastal intensive aquaculture.

As emerging contaminants, antibiotic resistance genes (ARGs) have become a public concern. This study aimed to investigate the occurrence and diversity of ARGs, and variation in the composition of bacterial communities in source water, drinking water treatment plants, and tap water in the Pearl River Delta region, South China. Various ARGs were present in the different types of water. Among the 27 target ARGs, floR and sul1 dominated in source water from three large rivers in the region. Pearson correlation analysis suggested that sul1, sul2, floR, and cmlA could be potential indicators for ARGs in water samples. The total abundance of the detected ARGs in tap water was much lower than that in source water. Sand filtration and sedimentation in drinking water treatment plants could effectively remove ARGs; in contrast, granular activated carbon filtration increased the abundance of ARGs. It was found that Pseudomonas may be involved in the proliferation and dissemination of ARGs in the studied drinking water treatment system. Bacteria and ARGs were still present in tap water after treatment, though they were significantly reduced. More research is needed to optimize the water treatment process for ARG removal.

The aim of this study was to investigate the contamination profiles of tetracycline, sulfonamide, and macrolide resistance genes, as well as integrons in sediments of Dongjiang River basin of South China by real time quantitative polymerase chain reaction. sul2 was the most abundant resistance gene, with the average concentration of 6.97×10(8) copies/g and 1.00×10(8) copies/g in the dry and wet seasons, respectively, followed by ermF, sul3, sul1, intI1, tetA, ermB, tetX, tetM, tetQ, tetO, tetW, tetS, ermC, and tetB. The abundance of intI2 gene was the lowest in the sediment samples. Significant correlations existed between the ARGs and sediment properties as well as metals (Cu and Zn) and corresponding antibiotic classes, suggesting that the contamination of ARGs is related to chemical pollution of the sediments in the river basin. Principal component analysis showed distinct groupings of the sampling sites, reflecting that human activities are the key player in the dissemination of ARGs in the catchment environment.

Integrated constructed wetlands (ICWs) are regarded as one of the most important removal technology for pollutants in rural domestic wastewaters. This study investigated the efficiency of an ICW consisting of a regulating pool, four surface and subsurface flow-constructed wetlands, and a stabilization unit for removing antibiotics and antibiotic resistance genes (ARGs) from rural domestic wastewaters. The results showed that antibiotics leucomycin, ofloxacin, lincomycin, and sulfamethazine, and ARGs sul1, sul2, tetM, and tetO were the predominant antibiotics and ARGs in the influent, respectively. The ICW system could significantly reduce most of the detected antibiotics and ARGs with their aqueous removal rates of 78 to 100 % and >99 %, respectively. Based on the measured concentrations, the total pollution loadings of antibiotics were 3,479 μg/day in the influent and 199 μg/day in the final effluent. Therefore, constructed wetlands could be a promising technology for rural wastewater in removing contaminants such as antibiotics and ARGs.