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BACKGROUND: Fermented rice flour (khao-khab, a non-glutinous rice) and related products are Thai traditional products. The types of acetic acid bacteria (AAB) microflora in khao-khab have not been reported. In this study, Acetobacter strains were isolated and identified based on the phenotypic and chemotaxonomic characteristics and molecular aspects. RESULTS: Twenty-five acetic acid bacteria isolated from fermented rice products and a starter for sweetened rice in Thailand by an enrichment culture approach, were assigned to the genus Acetobacter by phenotypic and chemotaxonomic characterisations. On the basis of the 16S rRNA gene sequence and 16S–23S rRNA gene ITS restriction analyses, 25 isolates were divided into six groups and identified at the specific level: (1) Group 1 included five isolates, which were identified as A. indonesiensis; (2) Group 2 included two isolates, which were identified as A. lovaniensis; (3) Group 3 included one isolate, which was identified as A. orientalis; (4) Group 4 included eleven isolates, which were identified as A. pasteurianus; (5) Group 5 included three isolates, which were identified as A. syzygii and (6) Group 6 included three isolates, which were unidentified and considered to constitute a new species. CONCLUSION: Results revealed that various Acetobacter species were distributed in Thai fermented rice flour and related products. A novel Acetobacter species was isolated from the product. Copyright © 2011 Society of Chemical Industry

Twenty-six strains of acetic acid bacteria were isolated from fruits, flowers and related materials collected in Thailand. They were divided into three genera, Acetobacter, Gluconobacter and Asaia, by phenotypic characterization and 16S rRNA gene sequence analyses. On the basis of 16S-23S rRNA gene internal transcribed spacer (16S-23S rDNA ITS) restriction and 16S rRNA gene sequence analyses, fourteen isolates assigned to the genus Acetobacter were divided into five groups: 1) Group 1A or A. tropicalis (one isolate); 2) Group 2A or A. orientalis (four isolates); 3) Group 3A or A. pasteurianus (five isolates); 4) Group 4A or A. syzygii (one isolate); and 5) Group 5A or A. ghanensis (three isolates). The eleven isolates assigned to the genus Gluconobacter were divided into three groups: 6) Group 1B or G. frateurii (four isolates); 7) Group 2B or G. japonicus (six isolates); and 8) Group 3B or unidentified (one isolate). The remaining isolate was placed into: 9) Group 1C or unidentified, which was assigned to the genus Asaia and considered to constitute a new species on the basis of the 16S rRNA gene sequence analysis and DNA-DNA hybridization.

Forty-five acetic acid bacteria, which were isolated from fruits, flowers and other materials collected in Thailand by an enrichment culture approach, were assigned to the genusGluconobacter by phenotypic and chemotaxonomic characterisations. On the basis of 16S–23S rRNA gene ITS restriction and 16S rRNA gene sequence analyses, the forty-five isolates were grouped into five groups and identified at the specific level as follows: 1) seventeen isolates were grouped into Group A and identified asG. oxydans; 2) twelve isolates were grouped into Group B and identified asG. cerinus; 3) nine isolates were grouped into Group C and identified asG. frateurii; 4) six isolates were included into Group D and identified asG. thailandicus; 5) one isolate was grouped into Group E, characterised by a restriction pattern comprised of 667 and 48-bp fragments inAvaII digestion, differing from those of strains of Group C orG. frateurii and Group D orG. thailandicus, and unidentified.

Three strains, RBY-1T, PHD-1 and PHD-2, were isolated from fruits in Thailand. The strains were Gram-negative, aerobic rods with polar flagella, produced acetic acid from ethanol and did not oxidize acetate or lactate. In phylogenetic trees based on 16S rRNA gene sequences and 16S–23S rRNA gene internal transcribed spacer (ITS) sequences, the strains formed a cluster separate from the type strains of recognized species of the genus Gluconobacter. The calculated 16S rRNA gene sequence and 16S–23S rRNA gene ITS sequence similarities were respectively 97.7–99.7 % and 77.3–98.1 %. DNA G+C contents ranged from 57.2 to 57.6 mol%. The strains showed high DNA–DNA relatedness of 100 % to one another, but low DNA–DNA relatedness of 11–34 % to the tested type strains of recognized Gluconobacter species. Q-10 was the major quinone. On the basis of the genotypic and phenotypic data obtained, the three strains clearly represent a novel species, for which the name Gluconobacter nephelii sp. nov. is proposed. The type strain is RBY-1T ( = BCC 36733T = NBRC 106061T = PCU 318T), whose DNA G+C content is 57.2 mol%.