The microbial composition and functional roles of different kombucha products in Singapore

Kombucha is a fermented tea drink traditionally known for its health-enhancing properties owing to the bioactive compounds generated by acetic acid bacteria (AAB) and lactic acid bacteria (LAB). In this study, we compared the distribution of AAB and LAB species and the contributing functional pathways across nine commercial kombucha products in Singapore using shotgun metagenomic sequencing. A high prevalence of Komagataeibacter species including Komagataeibacter saccharivorans (82.93% in B), Komagataeibacter xylinus (93.38% in D) and Komagataeibacter rhaeticus (92.20% and 30.62% in G and I) was detected in AAB-dominant kombucha. In contrast, LAB-dominant kombucha was largely represented by Bacillus coagulans (~99% in E and F) and Lactobacillus nagelii (~60% in H). Despite the differences in bacterial composition, both LAB-and AAB-dominant kombucha harbour pathways involved in the biosynthesis of short-chain fatty acids (SCFAs), branched and aromatic amino acids, organic acids and vitamin B12. Interestingly, fatty acid and beta-oxidation II (peroxisome) and fatty acid and beta-oxidation I were detected in the LAB but not the AAB-dominant kombucha.