Study On The Bacterial Community Characteristics Of Xueyu Cave And Shuiming Cave With Different Carbon Dioxide Concentrations

The karst area accounts for 15%of the ice-free area of global land.Karst cave is one of the most important forms of karst landform.Although the cave environment is dark,relatively closed,and oligotrophic,there are still abundant bacterial resources in the cave.However,the proportion of culturable bacteria in the cave is as low as that in other extreme environments.To fully understand the characteristics of bacterial community and ecological function in the cave environment,less culturable bacteria and more unculturable bacteria will be studied.Therefore,obtainment of a large amount of uncultivated bacteria in the cave has always been one of the hot spots of cave research.Chongqing Xueyu Cave?8751 ppm of CO₂ concentration?and Shuiming Cave?3303ppm of CO₂ concentration?were selected as the research objects.Sampling form cave was conducted on October 30,2018.The bacteria in the groundwater,sediment and rock wall were explored by pure bacterial culture and high-throughput sequencing in two caves.This paper analyzed the bacterial diversity deeply in the cave.In addition,this paper revealed the correlation between dominant OTUs and geochemical parameters?especially CO₂?,the ecological function of bacterial community and carbon utilization of representative strains in the cave.The main results were as follows.?1?Total 244 bacteria strains were isolated and purified,which belonged to 87different OTUs.Culturable bacteria were mainly composed of Proteobacteria,Actinobacteria,Firmicutes,Bacteroidetes and Deinococcus-Thermus.The dominant bacteria were Proteobacteria and Actinobacteria in two caves.?2?The CO₂ concentration was one of the important factors that affected the community of culturable bacteria and the ecological function in the karst caves.It was speculated that the negative?¹³C-CO₂ values of Xueyu Cave and Shuiming Cave might be attributed to the interaction of microorganisms and hydrogeochemistry.?3?The HCO₃^-/CO₂ value has an important influence on the diversity of bacterial communities in the cave.Bacterial diversity in water samples of Shuiming Cave and Xueyu Cave decreased with increasing HCO₃^-concentration.However,the bacterial diversity of Xueyu Cave?high HCO₃^-concentration?was higher than that of Shuiming Cave,which might be attributed to the higher pH in Xueyu Cave.There was no significant difference in bacterial diversity between the sediment samples of two caves.High CO₂concentration may inhibit the bacterial diversity of the rock wall of cave.?4?The bacterial community structure of the water samples of Shuiming Cave and Xueyu Cave were similar.The community structure of culturable bacteria in sediment and rock wall was very different,which might be attributed to the high concentration of HCO₃^-/CO₂.?5?There was difference in the ecological function of microorganisms in two caves.The chemoheterotrophy and photoautotrophy bacterial community accounted for higher proportion,which might be attributed to the lights in Xueyu Cave.However,there were tiny photoautotrophy bacteria in the rock wall of Shuiming Cave,which indicated that there was fluorescence or other invisible light in Shuiming Cave.The CO₂ concentration may be the main reason for the distribution of methanogenesis bacterial community.?6?The concentration of CO₂ may affect the diversity of bacteria in the cave by affecting the preference of bacteria for different types of carbon sources,which in turn affects the entire cave ecosystem.