We determined the 16S rRNA gene sequences of 302 strains of acetic acid bacteria isolated from Thailand. The isolates were divided into 35 sequence groups based on differences in 16S rRNA gene sequences. A phylogenetic tree constructed from these sequences showed that 5 strains should be classified into new genera in the family Acetobacteraceae. The other 297 strains were assigned to 33 sequence groups of 4 known genera Acetobacter, Asaia, Gluconacetobacter, and Gluconobacter. Seventeen strains belonging to Acetobacter were divided into 8 sequence groups (AB1-AB8). Seven groups except for AB2 were closely related to known Acetobacter species. AB2 was remote from known Acetobacter species. We sorted 150 strains of Asaia into 11 sequence groups (AS1-AS11). AS11 was distinct from all known Asaia species. Nine strains assigned to Gluconacetobacter showed 100% sequence similarity to Gluconacetobacter liquefaciens NBRC 12388^T. Further, 121 strains of Gluconobacter were divided into 13 sequence groups (GB1-GB13). Of these, GB1 and GB6 seemed to constitute 2 distinct lineages in the genus. Based on these results, 155 Thai strains were deposited from the BIOTEC culture collection (BCC) in the NITE Biological Resource Center (NBRC) for public use.

We examined the community compositions of bacteria in three non-axenic microalgal cultures, Chlorella saccharophila NIES-640, Ulothrix variabilis NIES-329 and Volvox aureus NIES-864, which had been maintained by subculturing without purification in the Microbial Culture Collection at the National Institute for Environmental Studies, Japan. Based on the similarity of the partial sequence of 16S rRNA gene, it was estimated that many species of bacteria in the cultures of U. variabilis NIES-329 and V. aureus NIES-864 are as-yet undescribed, in contrast to those in the C. saccharophila NIES-640 culture. The present and previous studies have indicated that some bacteria detected in the cultures might be associated with algae and/or can be hemi-selectively enriched with algae (e.g. Phyllobacterium bacteria and Chlorella algae). The present study indicates the potential usefulness of non-axenic cultures of algae as materials for studies on algal-bacterial associations.