Characteristics of Microbial Communities in Deep Geothermal Water and their geothermal Significance in Jizhong Geothermal Area, China

Abstract

Understanding the characteristics of microbial communities is quite important for the study of deep geothermal water microbiology. However, the characteristics of microbial communities in deep carbonate karst-fissure geothermal storage environment remain unclear. In order to explore the abundance, composition and function of microbial communities in the deep geothermal water from the deep carbonate rock karst-fissure geothermal storage environment, this study, taking shallow water and soil as the references, collected deep geothermal water samples by the pumping tests using the geothermal scientific drilling holes located in Jizhong geothermal area, China and also collected shallow water samples from farm irrigation wells and soil samples near the top of each drill hole, respectively for droplet digital PCR (ddPCR) assay, 16S rRNA gene high-throughput sequencing and functional predictions using PICRUSt software. The results show that deep geothermal water was rich in sulfate-reducing bacteria compared with shallow water and soil with an average of 4.0×103copies/mL±8.4×103copies/mL, 1.6×102±3.5×102 copies/mL and 1.5×103±1.2×103copies/g dw, respectively. There exist 38 phyla and 541 genera in the deep geothermal water of Jizhong geothermal area, of which bacteria are dominant (97.5%), whereas archaea are rare (2.5%), and characteristic microbial communities comprise mainly Firmicutes, Nitrospirae, Thermotogae and Euryarchaeota. The dominant bacterial genera include sulfate-reducing bacteria. These microbial communities in the deep geothermal water have relatively strong carbon fixation, fermentation and sulfate reduction, and weak methanogenesis and denitrification. Aerobic, mesophilic bacteria occurring in the deep geothermal water indicate that the deep geothermal water is recharged by the shallow water rich in proteobacteria under the condition of large flow pumping. This study has revealed that the deep carbonate rock karst-fracture geothermal reservoirs contain abundant microbial communities with various functions in Jizhong geothermal area, China. These microbial communities have great significance for the formation of chemical compositions of deep geothermal water and controlling corrosion and scaling during the development and utilization of geothermal energy.