Diversification of Bacterial Community Composition along a Temperature Gradient at a Thermal Spring

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To better understand the biogeography and relationship between temperature and community structure within microbial mats, the bacterial diversity of mats at a slightly alkaline, sulfide-containing hot spring was explored. Microbial mats that developed at temperatures between 75–52°C were collected from an area of approximately 1 m² in Nakabusa, Nagano, Japan. Bacterial 16S rRNA genes from these samples were examined by terminal restriction fragment length polymorphism (T-RFLP) and clone library analysis. T-RFLP profiles revealed 66 unique fragments (T-RFs). Based on total T-RFs observed in environmental profiles and clone libraries, a temperature effect on diversity was determined, with complexity in the community increasing as temperature decreased. The T-RF pattern indicated four distinct community assemblages related to temperature. Members of the Aquificales and particularly the sulfur-oxidizing bacterium Sulfurihydrogenibium were present at all temperatures and were the dominant component of mats taken at 75–67°C. Sulfide oxidation, which persisted throughout the temperature gradient, was the presumed dominant pathway of primary production above 67°C. As temperature decreased, successive additions of anoxygenic and oxygenic phototrophs increased primary productivity, allowing for diversification of the community.