Thermostable Nature of Hydrogen Production by Non-Sulfur Purple Photosynthetic Bacteria Isolated in Thailand

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Ten strains of non-sulfur purple photosynthetic bacteria were isolated from soil and water samples gathered in Bangkok and its surrounding area. The isolated strains from Thailand were divided into two groups, A1 to A4 and B1 to B6. They were identified as Rhodopseudomonas gelatinosa and Rhodopseudomonas sphaeroides, respectively. All strains grew well either at 30°C or 40°C, but failed to grow at 45°C. Strains belonging to group A had weak activities of nitrogenase (acetylene reduction) and hydrogen production, while strains of group B showed much higher activities than group A. The activities of nitrogenase and hydrogen production of isolates in Thailand were compared with those of isolates in Japan. The activities of isolated strains in Thailand at 40°C were almost equal to those at 30°C or even higher. On the other hand, both hydrogen production and the nitrogenase activity of isolates in Japan decreased significantly at 40°C as compared to the activities at 30°C. These results suggest an intrinsic thermostability in hydrogen production by the non-sulfur purple photosynthetic bacteria of Thailand. Among isolated strains in Thailand, strain B5 was the most active in nitrogenase and hydrogen production, and its activity was significantly higher than strain TN3 at 40°C. TN3 had been selected as the most active strain among isolates in the Sendai area.