[Effects of Organic Pollutants on the Bacterioplankton Community in Hangzhou Bay].

Hangzhou Bay suffers from intensive anthropogenic disturbances and a huge amount of terrestrial inputs, and thus has become one of the most seriously contaminated coastal zones in China. There is evidence that microbes play a dominant role in pollutant biodegradation and serve as biomarkers for pollution levels. However, it remains unclear how the bacterioplankton communities respond to organic contaminants. To fill this knowledge gap, we collected surface water samples (0.5 m below the surface layer) from 13 sites across Hangzhou Bay and 8 control sites across its adjacent offshore areas. Using Illumina sequencing based on analysis of the bacterial 16S rRNA gene, we explored the effects of increasing organic pollution levels on the bacterioplankton community compositions (BCCs). The results revealed that the organic pollution level (A) in Hangzhou Bay (13.2±1.6) was significantly (P<0.001) higher than in the control zone (5.4±3.0). The distribution and diversity of bacterioplankton communities were significantly distinct between the two zones. The dominant bacterioplankton lineages in Hangzhou Bay were γ-Proteobacteria (24.4%±5.5%), α-Proteobacteria (16.5%±7.7%), and Planctomycetes (13.9%±8.6%), whereas those in the adjacent zones were Cyanobacteria (20.1%±7.5%), Bacteroidetes (18.4%±1.5%), Actinobacteria (17.5%±4.2%), γ-Proteobacteria (16.6%±1.2%), and α-Proteobacteria (14.3%±1.7%). Multivariate regression tree (MRT) analysis showed that the bacterioplankton community diversity was primarily affected by suspended particulates (SP), nitrite, oil, and organic pollutants, which respectively explained 22.0%, 6.5%, 6.0%, and 5.5% of the variance in diversity. Redundancy analysis (RDA) illustrated that the bacterioplankton community distribution was controlled by organic pollutants, COD, Chla, TN, nitrate, and salinity, which cumulatively governed 71.0% of the variation in BCCs. Organic pollutants alone controlled 6.5% variance, which was higher than any other single factor. Additionally, 35 sensitive species were identified via the indicator value method and their relative abundances were significantly associated (P<0.05 in each case) with the organic pollution level, thereby indicating their potential for evaluating coastal pollution. Collectively, our work demonstrates that BCCs are sensitive to coastal pollution and provides biomarkers for elevated pollution levels.

Starvation stress affects the interplay among shrimp gut microbiota, digestion and immune activities.

Aquatic animals are frequently suffered from starvation due to restricted food availability or deprivation. It is currently known that gut microbiota assists host in nutrient acquisition. Thus, exploring the gut microbiota responses would improve our understanding on physiological adaptation to starvation. To achieve this, we investigated how the gut microbiota and shrimp digestion and immune activities were affected under starvation stress. The results showed that the measured digestion activities in starved shrimp were significantly lower than in normal cohorts; while the measured immune activities exhibited an opposite trend. A structural equation modeling (SEM) revealed that changes in the gut bacterial community were directly related to digestive and immune enzyme activities, which in turn markedly affected shrimp growth traits. Notably, several gut bacterial indicators that characterized the shrimp nutrient status were identified, with more abundant opportunistic pathogens in starved shrimp, although there were no statistical differences in the overall diversity and the structures of gut bacterial communities between starved and normal shrimp. Starved shrimp exhibited less connected and cooperative interspecies interaction as compared with normal cohorts. Additionally, the functional pathways involved in carbohydrate and protein digestion, glycan biosynthesis, lipid and enzyme metabolism remarkably decreased in starved shrimp. These attenuations could increase the susceptibility of starved shrimp to pathogens infection. In summary, this study provides novel insights into the interplay among shrimp digestion, immune activities and gut microbiota in response to starvation stress.

[Effects of Coastal Organic Pollution on Bacterioplankton Community in Sanmen Bay].

Coastal organic pollution has become a serious problem, thus it is imperative to assess the potential effects on the marine environment. The microbes are generally the first responders to environmental perturbation, which may serve as biological indicators for pollution levels. In this study, we collected surface seawater samples from Sanmen Bay and adjacent Yushan Reserve. Using an Illumina sequencing based analysis of bacterial 16S rRNA gene, we explored the effect of organic pollution on the bacterioplankton community compositions (BCCs). The results showed that the organic pollution (A) was 4.57±2.41 at Sanmen Bay, which was significantly higher (P<0.001) than that in Yushan Reserve (0.43±0.74). The bacterial diversity and community compositions differed significantly between the two locations. Specifically, the relative abundance of Actinobacteria, α-Proteobacteria, ß-Proteobacteria, SAR406 in Sanmen Bay was significantly higher than that in Yushan Reserve, while Bacteroidetes, Cyanobacteria, Planctomycetes exhibited an opposite change pattern. A multivariate regression tree analysis showed that the bacterial diversity was primarily affected by water pH, organic pollution and chlorophyll a levels, which respectively explained 27.7%, 15.6% and 6.7% variance in bacterial diversity. A redundancy analysis (RDA) revealed that the bacterioplankton community was significantly controlled by pH, salinity and organic pollution, which cumulatively explained 14.8% of the variation in BCCs. In addition, the geographic distance was significantly (P <0.001) correlated with BCCs, accounting for 4.42% variance, which suggested that the spatial distribution of bacterioplankton community was non-random. Moreover, this study screened 23 sensitive bacterial families, whose relative abundances were significantly associated the organic pollution. For a given bacterial family, the change pattern of relative abundance was consistent with its known function, thus holding the potential for indicating organic pollution levels. To conclude, this study showed that the increasing coastal organic pollution had altered BCCs, and enriched the relative abundances of potential pathogens. Furthermore, the sensitive bio-indicators were screened for evaluating the increasing organic pollution level.

[Responses of Plankton Microeukaryotic Community to Increasing Temperatures Created by Power Plant Thermal Discharges].

Plankton microeukaryotes are primary producers, bacterial grazers and parasites in the ocean, thus contributing essential roles in marine ecosystem stability. For this reason, understanding how the microeukaryotic community responds to increasing temperature created by thermal discharges is key to evaluating the ecological and environmental consequences of a power plant. In this study, using an Illumina sequencing based analysis of eukaryotic 18S rDNA gene, we investigated the compositions of microeukaryotic community along a thermal gradient caused by the discharge from the Wusha Mountain power plant in Xiangshan Bay. The plankton microeukaryotic communities were dominated by Protalveolata, Ciliophora, Dinoflagellata and Cercozoa. A multivariate regression tree revealed that mircoeukaryotic diversity was primarily controlled by dissolved oxygen (DO), followed by nitrate and temperature. Thermal discharge significantly altered the compositions of microeukaryotic community, evidenced by an analysis of similarity (Global RANOSIM=0.422, P<0.001). A forward selection procedure showed that the variations of microeukaryotic community were primarily shaped by geographic distance, DO, chlorophyll a, and temperature. The spatial distribution of microeukaryotic community followed a distance-decay for similarity relationship, with a turnover of 0.002. In addition, 15 sensitive eukaryotic families were screened, the relative abundances of which were significantly associated with the discharge-induced temperature gradient. For a given eukaryotic family, the pattern of enrichment or decline was consistent with its known ecological function, which could be served as bio-indicators for temperature anomalies. Collectively, this study demonstrates the spatial pattern of microeukaryotic community in responses to increasing temperature, and provides sensitive bio-indicators for evaluating the ecological consequences of thermal discharge.