[Bacterial Community Composition in Channel Sediment in Response to Mariculture Wastewater Drainage].

The impact of mariculture on the ecological environment of sediments in surrounding waters is intensely debated. Microbial communities are considered to be keystone indicators of lineage responses to changes in environmental quality. To examine the mariculture effects, we collected channel sediment from four sites in the culture area including oneintake canal, one outfall, and two outlet canals. On the basis of bacterial 16S rRNA gene and phospholipid fatty acid (PLFA) technology, we used Illumina MiSeq sequencing applied to the analysis results to explore the effects of mariculture wastewater drainage on the bacterial community structures in the sediment. The results revealed that Proteobacteria, including γ-Proteobacteria, δ-Proteobacteria, and α-Proteobacteria, were the dominant lineages of bacteria at the four sites. The microbial biomass of the sediment increased significantly owing to the effects of mariculture wastewater drainage. The relative abundance of Actinobacteria and ammoniated microorganisms decreased, whereas the relative abundance of Bacteroidetes increased. The results of non-metric multidimensional scaling (NMDS) analysis indicated that most of the sediment bacterial communities clustered by influent and effluent. The diversity indicated that the mariculture wastewater drainage decreased the bacterial diversity, and redundancy analysis (RDA) indicated that the most obvious correlation occurred between ammonia nitrogen and bacterial community structures. In summary, the mariculture wastewater drainage resulted in significant changes in the physical and chemical properties and structures of bacterial communities in the aquaculture channel sediment. This indicates that the long-term direct discharge of aquaculture wastewater would excessively contaminate a channel environment and might further pose a threat to the offshore ecological environment.

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.

Microbial Communities and Diversities in Mudflat Sediments Analyzed Using a Modified Metatranscriptomic Method.

Intertidal mudflats are land-sea interaction areas and play important roles in global nutrient cycles. However, a comprehensive understanding of microbial communities in these mudflats remains elusive. In this study, mudflat sediment samples from the Dongtan wetland of Chongming Island, the largest alluvial island in the world, were collected. Using a modified metatranscriptomic method, the depth-wise distributions of potentially active microbial communities were investigated based on small subunit ribosomal RNA (SSU rRNA) sequences. Multiple environmental factors were also measured and analyzed in conjunction with the prokaryotic composition profiles. A prokaryotic diversity analysis based on the metatranscriptome datasets revealed two or threefold higher diversity indices (associated with potentially active microbes participating in biogeochemical processes in Dongtan) compared with the diversity indices based on 16S rRNA gene amplicons. Bacteria were numerically dominant relative to archaea, and the potentially active prokaryotic taxa were mostly assigned to the bacterial phyla Chloroflexi, Acidobacteria, and Bacteroidetes and the classes Delta- and Gamma-proteobacteria, along with the archaeal lineages phylum Bathyarchaeota and the order Thermoplasmatales. The total nitrogen and carbon content of the sediment samples were environmental factors that significantly affected the depth-wise distributions of both bacterial and archaeal communities. Furthermore, the activity of potentially active taxa (including the prevalent order Desulfobacterales and family Anaerolineaceae) appeared to be significantly underestimated by PCR-based methods, notably at the DNA level, and indicates that using normal PCR amplification of DNA limits the study of potential microbial activity. This is the first study of potentially active microbial communities in depth-wise sediments from Dongtan. The improved knowledge of microbial communities in Dongtan provides a foundation for exploring biogeochemical cycling and microbial functions.