Prior exposure to ciprofloxacin disrupts intestinal homeostasis and predisposes ayu ( Plecoglossus altivelis) to subsequent Pseudomonas plecoglossicida-induced infection.

With the rapid development of intensive farming, the aquaculture industry uses a great many antibiotics for the prevention and treatment of bacterial diseases. Despite their therapeutic functions, the overuse and accumulation of antibiotics also pose a threat to aquaculture organisms. In the present study, ayu ( Plecoglossus altivelis) was used as a fish model to study the impacts of ciprofloxacin (CIP) overuse on intestinal homeostasis and immune response during subsequent Pseudomonas plecoglossicida infection. Based on 16S rRNA gene amplification and Illumina sequencing, we found that CIP pre-exposure caused significant variation in intestinal microbiota, including increased species richness, altered microbiota composition and interaction networks, and increased metabolic dysfunction. Furthermore, immunohistochemical analysis indicated that CIP pre-exposure resulted in severe mucosal layer damage, goblet cell reduction, and epithelial cell necrosis of the intestinal barrier in infected ayu. Quantitative real-time polymerase chain reaction (qRT-PCR) showed that disruption of intestinal homeostasis impaired systemic anti-infection immune responses in the intestine, gill, spleen, and head kidney, while inhibiting IL-1ß, TNF-α, and IL-10 expression and promoting TGF-ß expression. Our findings indicated that CIP administration can directly affect intestinal microbiota composition and intestinal integrity in ayu fish. This perturbation of intestinal homeostasis is likely responsible for the lower survival rate of hosts following subsequent infection as the capacity to mount an effective immune response is compromised. This study also provides preliminary clues for understanding the effects of antibiotic overuse on higher vertebrates through trophic transfer.

Immune and gut bacterial successions of large yellow croaker (Larimichthys crocea) during Pseudomonas plecoglossicida infection.

Large yellow croaker (Larimichthys crocea, LYC) aquaculture is being threatened by intensive infectious diseases. Relevant studies have focused on LYC immune responses to infection. By contrast, little is known how and to what extent the gut microbiota responds to infection. Here, we explored the interactions between LYC immune responses and gut bacterial communities during Pseudomonas plecoglossicida infection. P. plecoglossicida successfully colonized into LYC gut microbiota, resulting in an increasing mortality rate. Relative gene expressions of pro-inflammatory cytokines (TNF-α1, TNF-α2 and IL-1ß) and anti-inflammatory cytokine (IL-10) were consistently and significantly induced by P. plecoglossicida infection, whereas non-specific immune enzymes activities were only enhanced at the early infection stages. P. plecoglossicida infection caused an irreversible disruption in the gut microbiota, of which infection and hours post infection constrained 16.2% and 5.6% variations, respectively. In addition, top 18 discriminatory taxa that were responsible for the difference between treatments were identified, whose abundances were significantly associated with the immune activities of LYC. Using a structural equation modeling (SEM), we found that gut bacterial communities were primarily governed by the conjointly direct (-0.33) and indirect (0) effects of infection, which subsequently affect host immune responses. Our results suggest that an irreversible dysbiosis in gut microbiota could be the causality of increasing mortality. To our knowledge, this is the first study to provide an integrated overview among pathogen infection, immune response and gut microbiota of LYC.

Current understanding on the roles of gut microbiota in fish disease and immunity.

Intensive aquaculture has increased the severity and frequency of fish diseases. Given the functional importance of gut microbiota in various facets of host physiology, modulation of this microbiota is a feasible strategy to mitigate emerging diseases in aquaculture. To achieve this, a fundamental understanding of the interplay among fish health, microbiota, and invading pathogens is required. This mini-review focuses on current knowledge regarding the associations between fish diseases, dysbiosis of gut microbiota, and immune responses. Furthermore, updated research on fish disease from an ecological perspective is discussed, including colonization resistance imposed by commensals and strategies used by pathogens to overcome resistance. We also propose several directions for future research, such as exploration of the causal links between fish diseases and specific taxa, and identification of universal gut microbial biomarkers for rapid disease diagnosis.

[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.

[Intestinal bacterial community is indicative for the healthy status of Litopenaeus vannamei].

High density and intensive Litopenaeus vannamei aquaculture has increased the frequency of shrimp disease, however, it remains uncertain whether change in intestinal bacteria could be indicative of shrimp health state (healthy or diseased). Therefore, we collected water and shrimp intestine samples from ponds with or without diseased shrimps. Using bacterial 16S rRNA gene as a biomarker, the bacterial community structure and diversity were evaluated with the Illumina MiSeq sequencing technique. The results showed that the variations of bacterioplankton community were primarily shaped by the levels of NO2(-)-N, chlorophyll a and PO4(3-)-P. Bacterial diversity was signif-7 icantly lower in diseased shrimps than in healthy ones. Using a response ratio analysis, we screened 28 operational taxonomic units (OTUs), and their abundances significantly changed in the intestines between healthy and diseased shrimps. In general, the abundances of OTUs belonged to Actinobacteria, Flavobacteria and Bacilli significantly decreased in diseased shrimps compared with those in healthy shrimps., while the OTUs affiliated to Clostridia showed an opposite pattern. In addition, we obtained 61 indicator species that primarily affiliated to Bacteroidetes, Proteobacteria, Firmicutes, Planctomycetes and Actinobacteria. Notably, the identified indicator taxa exhibited clearly discriminative patterns among habitats (water or intestine) and health status. Collectively, this study provided scientific information for development of new probiotics and disease prevention.

[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.