Aims: To investigate the occurrence and distribution of thermo-acidophilic bacteria (TAB) associated with various commercial fruit crop soils in Japan and to assess their ability to produce the odorous phenolic compound, guaiacol.
Methods and results: Phylogenetic analysis based on the 5' end of the 16S rRNA gene (approximately 500 bp), was performed on 62 TAB isolated from the soil of several Japanese fruit orchards. The results suggested that 60 of the bacterial strains analysed belonged to the genus Alicyclobacillus, while the remaining two belonged to the genus Bacillus. The majority of strains (58%) were identified as Alicyclobacillus acidoterrestris. This group partitioned into three phylogenetically distinct subgroups (A-C). Isolates identified as A. acidiphilus (two strains), A. acidoterrestris (36 strains), and A. hesperidum subsp. aigle (one strain), produced guaiacol from vanillic acid. Levels of guaiacol production varied significantly among strains. The guaiacol producing phenotype was conserved among certain species, however no correlation was observed between levels of guaiacol production and 16S rRNA gene-based phylogenetic relatedness.
Conclusions: Alicyclobacillus acidoterrestris and Alicyclobacillus contaminans were widely distributed among various fruit orchards in Japan. Guaiacol production was common at the species/subspecies level; however the amount of guaiacol produced by each strain varied significantly.
Significance and impact of the study: This study provides a comprehensive phylogenetic survey of Alicyclobacillus species in Japanese fruit orchards. Quality control standards for guaiacol producing Alicyclobacillus have also been described.