Complete Genome Sequence and Comparative Genomics of Acetobacter cerevisiae KSO5 (KACC 92352P) Provide Genome-Based Insights into Acid Tolerance

Acetobacter cerevisiae KSO5 is an indigenous strain isolated from Korean fruit vinegar and is a potential starter candidate for vinegar fermentation. Here, we report the first complete circular genome of KSO5, comprising a 3.3 Mb chromosome and two plasmids encoding 2898 genes. Core-genome phylogeny clearly placed KSO5 within the A. cerevisiae clade, supported by ANI (97%) and dDDH (71%) values. Comparative analysis with seven draft A. cerevisiae genomes identified strain-specific genomic islands, mobile genetic elements, and plasmid-borne modules potentially related to genetic stability. Comparative COG profiling suggested enhanced potential for carbohydrate utilization, redox balancing, membrane transport, and stress adaptation within a conserved Acetobacter genomic background. The genome encoded a periplasmic oxidative fermentation system, including membrane-bound pyrroloquinoline quinone-dependent alcohol dehydrogenase and molybdopterin-dependent aldehyde dehydrogenase, together with predicted acetate-handling routes that may reduce intracellular acetate accumulation. Consistent with these features, KSO5 maintained growth and titratable acidity production up to 9% ethanol, with the strongest performance at 7–9% ethanol, whereas both traits declined markedly at 10% ethanol. In 5% ethanol medium, KSO5 also showed high ethanol consumption, comparable to that of A. pasteurianus LMG 1262 and higher than that of most reference strains. These findings link the genomic features of KSO5 to efficient ethanol oxidation, sustained acidification, and stable growth, supporting its potential as a starter strain for vinegar fermentation.