Bacterial populations in epilithic biofilms along two oligotrophic rivers in the Tohoku region in Japan

Bacterial populations in epilithic biofi lms collected from two distinct oligotrophic rivers of Japan were studied using denaturing gradient gel electrophoresis (DGGE). PCR-DGGE of the 16S rRNA gene and subsequent sequencing analysis suggested that in freshwater biofi lms, members of the Cytophaga-Flavobacterium-Bacteroides (CFB) group were the most dominant, followed by those of α-, β-, γ-, and δ-Proteobacteria; Leptospiraceae; and unidentifi ed bacteria. Members of the CFB group, α-Proteobacteria, and cyanobacteria/plastid DNA were also detected from the biofi lms collected from the estuary site, but the species in these samples differed from those detected in biofi lms in the freshwater areas of the rivers. A comparison between the determined sequences revealed that similar bacterial species existed in biofi lms at different sites of a river, and identical species existed in biofi lms of distinct rivers. The results suggested that bacterial species in biofi lms found in the estuary were different from those found in the freshwater areas of the rivers; however, the common bacterial species were distributed in biofi lms collected from not only different sites along the same river but also sites in distinct oligotrophic rivers.