Seasonal Succession of Bacterial Communities in Three Eutrophic Freshwater Lakes

Impact of Sublethal Concentrations of Nitrite on Goldfish (Carassius auratus) Microbiomes

Elevated concentrations of nitrite are toxic to fish and can cause a myriad of well documented issues. However, the effects of sublethal concentrations of nitrite on fish health, and specifically, fish tissue microbiomes have not been studied. To test the effects of nitrite exposure, goldfish were exposed to sublethal concentrations of nitrite, 0.0 mM, 0.1 mM, and 1.0 mM, for 2 months. The bacteria in the nose, skin, gills, and water were then extracted and sequenced to identify changes to the microbial composition. The water microbiome was not significantly changed by the added nitrite; however, each of the tissue microbiomes was changed by at least one of the treatments. The skin and gill microbiomes were significantly different between the control and 1.0 mM treatment and the nose microbiome showed significant changes between the control and both the 0.1 mM and 1.0 mM treatments. Thus, sublethal concentrations of nitrite in the environment caused a shift in the fish tissue microbiomes independently of the water microbiome. These changes could lead to an increased chance of infection, disrupt organ systems, and raise the mortality rate of fish. In systems with high nitrite concentrations, like intensive aquaculture setups or polluted areas, the effects of nitrite on the microbiomes could negatively affect fish populations.

Chronic exposure to deltamethrin disrupts intestinal health and intestinal microbiota in juvenile crucian carp

The indiscriminate use of deltamethrin in agriculture and aquaculture can lead to residues increased in many regions, which poses negative impacts on intestinal health of aquatic organisms. Although the potential toxicity of deltamethrin have recently attracted attention, the comprehensive studies on intestinal injuries after chronic deltamethrin exposure remain poorly understood. Herein, in a 28-day chronic toxicity test, crucian carp expose to different concentrations of deltamethrin (0, 0.3, and 0.6 μg/L) were used as the research object. We found that the morphology changes and increased goblet cells in intestinal tissue, and the extent of tissue injury increased along with the increasing exposure dose of deltamethrin. Additionally, the genes expression of antioxidant activity (Cu/Zn superoxide dismutase (Cu-Zn SOD), glutathione peroxidase 1 (GPX1), and catalase (CAT)), inflammatory response (tumor necrosis factor alpha (TNFα), interferon gamma (IFNγ), and interleukin 1 beta (IL-1β)), and tight junctions (Claudin 12 (CLDN12), and tight junction protein 1 (ZO-1)) dramatically increased. Meanwhile, the apoptosis and autophagy process were triggered through caspase-9 cascade and autophagy related 5 (ATG5)- autophagy related 12 (ATG12) conjugate. Besides, chronic deltamethrin exposure increased the amount of Proteobacteria and Verrucomicrobiota, while decreased Fusobacteriota abundance, resulting in intestinal microbiota function disorders. In summary, our results highlight that chronic exposure to deltamethrin cause serious intestinal toxicity and results in physiological changes and intestinal flora disturbances.

Different Assembly Patterns of Planktonic and Sedimentary Bacterial Community in a Few Connected Eutrophic Lakes

The mechanism of bacterial community assembly has been the hot spot in the field of microbial ecology and it is difficult to quantitatively estimate the influences of different ecological processes. Here, a total of 23 pairs of planktonic and sedimentary samples were collected from five lakes in Wuhan, China. significant higher α-diversity (p < 0.001) and β-diversity (p < 0.001) of bacterial communities were observed in sediment than those in water. Some phylum had linear relationships with the comprehensive TSI (TSIc) by regression analysis. Non-metric multidimensional scaling (NMDS) and redundancy analysis (RDA) revealed that the depth of water, NO3−-N, NH4+-N, PO43−, and CODcr were the key environmental variables in planktonic bacterial communities, whereas in sediment they were the depth, NO3−-N, and NH4+-N. Furthermore, variation partitioning analysis (VPA) showed that spatial and environmental factors could only explain 40.2% and 27.9% of the variation in planktonic and sedimentary bacterial communities, respectively. More importantly, null model analysis suggested that different assembly mechanisms were found between in water and in sediment with the fact that planktonic bacterial community assembly was mainly driven by dispersal limitation process whereas variable selection process played a vital role in that of sediment.