Thermotolerant purple nonsulfur bacteria from New Zealand geothermal areas
Purple nonsulfur bacteria (PNSB) are a metabolically and nutritionally diverse group of photosynthetic organisms that have been isolated from many environments. Three thermotolerant or mildly thermophilic strains are known from thermal areas in the United States and Japan. Only mesophilic isolates have been obtained from Russian hot springs. Enrichment cultures selective for PNSB were set up on samples taken from a range of New Zealand geothermal areas. Photosynthetic purple bacteria could readily be isolated from Waimangu and Orakei Korako samples, but could not be isolated from Tokaanu mats. In total, 35 isolates belonging to the genera Rhodopseudomonas, Rhodoplanes, Blastochloris, Rubrivivax, Rhodomicrobium, Rhodospirillum and Phaeospirillum were obtained from 18 positive sample sites. The majority of isolates grew optimally around 40°C and had temperature maxima ranging from 43 to 47°C. Other isolates had lower optima and were thermotolerant. Many Rhodoplanes and Blastochloris isolates represented novel genospecies, though some could not be unambiguously distinguished by their phenotypic properties. The novel species Rhodoplanes venustus sp. nov., Rhodoplanes segnis sp. nov., and Phaeospirillum tepidarium sp. nov. are proposed. Molecular methods were used to specifically detect photosynthetic purple bacteria. A clone library of photosynthetic reaction centre pufL genes amplified from an Orakei Korako mat sample was constructed and screened. No clone sequences were identical to those of organisms isolated previously or in the current study. The clone library was dominated by sequences attributable to aerobic anoxygenic phototrophic bacteria. Four novel pufL sequences attributable to purple nonsulfur bacteria were obtained. Rhodoplanes strains possessed the ability to use nicotinic acid as sole source of carbon and nitrogen, via a pathway that includes 6-hydroxynicotinate and glutarate as intermediates, as are in the Azorhizobium caulinodans pathway. Unlike other nicotinic-acid degrading organisms, growth of Rhodoplanes on nicotinate was not inhibited by addition of tungstate.
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