Isolation and Characterization of Phototrophic Purple Nonsulfur Bacteria from Chloroflexus and Cyanobacterial Mats in Hot Springs

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Chloroflexus and cyanobacterial mats developing at 50-65°C in Nakanoyu and Nakabusa hot springs, Japan, were collected and cultivated phototrophically at 50 and 37°C. Chloroflexus organisms grew when incubated at 50°C, whereas the incubation at 37°C resulted in the enrichment of pink- to brown-colored cultures, from which different species of phototrophic purple nonsulfur (PPNS) bacteria were isolated. The majority of the isolates grew at temperatures of up to 45°C and optimally at around 40°C. The high frequencies of the occurrence of PPNS bacteria in hot spring microbial mats suggest that these environments offer a favorable ecological niche for these bacteria.