Importance of Komagataeibacter in submerged fermented rice vinegar microbiome

Abstract

Rice vinegar is a common condiment in Japan, and the submerged fermentation method is used for the industrial production of rice vinegar. Acetic acid bacteria are known to have a significant influence on fermentation characteristics during vinegar brewing, and clarification of the types of microorganisms and their roles in acetic acid fermentation in submerged fermentation rice vinegar production may be useful for optimization of the fermentation process. In this study, we investigated the changes in the microbiome in submerged fermented rice vinegar for the entire fermentation process, which has not been investigated before. The investigation of the bacterial community showed that the percentage of acetic acid bacteria of the genus Komagataeibacter increased rapidly when the ethanol concentration started to decrease, then maintained a high percentage of dominance in both rice vinegars with different acidity levels. Metagenomic analysis results for the starter culture suggested that the acetic acid bacteria that ferment in submerged fermented rice vinegar is Komagataeibacter europaeus, which is resistant to high acetic acid concentration, and that this strain is closely related to the strain isolated from submerged fermented vinegar produced in Europe. This study provides basic information on the microorganisms in submerged fermentation of rice vinegar and may be useful for optimizing the fermentation process in rice vinegar brewing.