This paper is the result of geothermal survey engineering.
[Objective] Researches on microbial community in geothermal systems is key to indicate geochemical environment and evolution of thermal fluids. Previous researches have shown that the thermal water in Lindian geothermal field is highly reducing and is rich in methane. The objective of this paper is to characterize the microbial diversity and community structure of the thermal water. [Methods] A total of 9 thermal water samples were collected and tested during exploitation and non-exploitation periods, and the microbial diversity, community structure and functional genes of the samples were analyzed. [Results] The dominant bacterial genera in the thermal water is mainly Acinetobacter, which is different from most geothermal systems reported, but are similar to that of oil fields. The bacterial diversity of the thermal waters during the exploitation period and the non-exploitation period is significantly different, i.e., the bacterial diversity in the non-exploitation period is higher than that in the exploitation period, while the archaeal diversity is not affected significantly by exploitation. The dominant archaea are mainly Euryarchaeota methanogens. Functional gene prediction of archaea shows that methane production in Lindian geothermal field is dominated by hydrogenotrophic methanogenesis, and secondarily by disproportionation of methyl groups and reduction of methyl compounds with H₂. [Conclusions] The microbial diversity and community structure of the thermal waters from Lindian geothermal field is relatively unique, which is related to the high content of organic matters and thermal water exploitation.