Study On Microbial Diversity And Its Dominant Acinetobacter Ecotoxicology In Wanzhou Section Of Three Gorges Reservoir

The Three Gorges Reservoir(TGR)is an important freshwater resource in China.The microbial diversity plays an important role in maintaining the ecological health of the reservoir water.It was found that the water pollution and water level changes in the TGR would to changes of microbial diversity in the water ecosystem,which would directly affect the structure and function of microbial community in the water environment,and may lead to water ecological imbalance in the TGR,resulting in negative ecological effects.There are few studies on the structure and functional diversity of the microbial community,as well as the ecotoxicological effects of dominant bacteria,in the TGR.We performed high-throughput sequencing(16S r RNA sequencing)and environmental functional Geochip analysis for the microbial community and functional gene diversity in different waters of the Wanzhou section of the TGR.We isolated and identified the dominant bacteria in the waters of the TGR.We further used a model organism,Caenorhabditis elegans,to determine toxic effect and toxicological mechanism after exposure to dominant bacteria.The analysis of microbial diversity indicated that bacterial species in the Wanzhou section of the TGR were rich,and the diversity of bacteria in different waters was different.The species richness order from high to low was the backwater area of the mainstream,the the downstream of the mainstream,the north side of the mainstream,the upstream of the mainstream,and the south side of the mainstream.There was a certain relationship between the abundance of species and COD(Chemical oxygen demand),TUR(turbidity),and TDS(total dissolved solids).The evolution analysis of dominant bacteria species in water showed that at the level of phylum and genus,Proteobacteria was dominant phyla,which accounted for 51.0%of total abundance.Acinetobacter was dominant genus,which accounted for 27.4% of total abundance.Bacterial species in backwater area were more abundant compared with in other regions.The analysis of microbial functional gene diversity showed that there were differences in microbial functional gene diversity in different waters of the Wanzhou section of the TGR.Common and characteristic functional genes in backwater areas were most abundant.The diversities of microbial functional genes in north and south sides,upstream and downstreamof the mainstream were relatively consistent.The composition and difference analysis of key genes of carbon and nitrogen cycle showed that there were differences in genetic diversity of microorganisms involved in carbon and nitrogen metabolism in different waters.The functional gene diversities involved in carbon fixation,carbon degradation and denitrification were most abundant,followed by methane metabolism,ammoniation and nitrogen fixation.The abundance of functional genes were highest in the backwater area.Twenty-one dominant Acinetobacter strains were isolated and identified from waters in the Wanzhou section of the TGR.These 21 isolates and 5 reference strains were used for exposure to C.elegans.Acinetobacter AC1,AC15,AC18,and AC21 isolates and A.baumannii,A.junii,and A.lwoffii reference strains could significantly shorten lifespans,reduce locomotion behavior,and induce ROS production in C.elegans.Moreover,4 pathogenic strains of Acinetobacter(AC1,AC15,AC18,and AC21)and 3 reference strains(A.baumannii,A.junii,and A.lwoffii)could significantly increase the expressions of some antimicrobial genes(lys-1,spp-12,lys-7,dod-6,spp-1,dod-22,lys-8,and F55G11.4)and SOD-3::GFP.In wild-type C.elegans,infection with Acinetobacter pathogenic bacteria could significantly increase expressions of daf-16 and sod-3 in the insulin signaling pathway,and pmk-1 and gst-4in the p38 MAPK signaling pathway,which are required for the control of innate immune response.Compared with wild-type,the more severe lifespan reduction,ROS production,and formation of Acinetobacter colonies were detected in daf-16(mu86),sod-3(RNAi),pmk-1(RNAi),and gst-4(RNAi)nematodes.In conclusion,there are differences in microbial communities and functional gene diversity in different waters of Wanzhou section of the TGR.The species and functional gene abundances in backwater area of the mainstream is more abundant,which may be related to environmental factors,such as water pollution.Acinetobacter is the dominant bacteria genus in Wanzhou section of the TGR.Some pathogenic strains showed strong virulence effects on C.elegans,indicating their ecological risk in the TGR.Our results are helpful for understanding the water ecological health of the TGR,preventing and controlling toxic effects of water ecological environment of the TGR,and providing scientific clues and strategies for assessing water quality and biological safety.