Molecular and culture-based analysis of aerobic phototrophic bacterial diversity

Abstract

The aerobic phototrophic bacteria (APB) are the aerobes capable of producing functional photosynthetic apparatus in aerobic condition in contrast to typical ‘anaerobic’ anoxygenic phototrophic bacteria. Because of atypical phototrophic ability and ecological abundance, APB have been investigated contnuously since 1970’s. A lot of strains of APB were isolated from various habitats and classified into various genera of alpha- and beta-Proteobacteria. It was reported that APB were abundant and might have significant roles in surface ocean. Phylogenetic distribution of APB was known to be more diverse than expected. To understand ecological roles and phylogenetic position of APB, it is necessary to get more information about APB. In this study, we isolated APB from various habitats of soil and freshwater. For screening, we adopted a molecular approach amplifying pufLM gene from APB candidates forming colored colonies. Diversity and phylogeny of the isolates were analyzed by comparing 16S rDNA and pufM gene sequences. We isolated 292 strains showing color, and screened 87 potential APB strains by performing PCR amplification of pufLM gene. We found most of soil and freshwater isolates was in the genus Methylobacterium and family Sphingomonadaceae indicating microorganisms in these groups might be a major APB in terrestrial and aquatic environments. Some of these isolates were closely related to genus Sphingomonas, Novosphingobium and Sphingopyxis previously regarded as non-phototrophic bacteria. Additionally, we found a new group of APB in family Sphingomonadaceae. Numbers of the isolates containing pufLM gene do not produce Bacteriochlorophyll a (BChl a) under given culture condition. The BChl a production was related to pufLM gene phylogeny. From the cloning of pufM gene amplified from microbial communities of soil and freshwater, we could find pufM gene sequences similiar to those from isolated strains in this suvery and new pufM gene sequences different with kno...