In vitro thermal adaptation of mesophilic Acetobacter pasteurianus NBRC 3283 generates thermotolerant strains with evolutionary trade-offs.

Thermotolerant strains are critical for low-cost high temperature fermentation. In this study, we carried out the thermal adaptation of A. pasteurianus IFO 3283-32 under acetic acid fermentation conditions using an experimental evolution approach from 37ºC to 40ºC. The adapted strain exhibited an increased growth and acetic acid fermentation ability at high temperatures, however, with the trade-off response of the opposite phenotype at low temperatures. Genome analysis followed by PCR sequencing showed that the most adapted strain had 11 mutations, a single 64-kb large deletion, and a single plasmid loss. Comparative phenotypic analysis showed that at least the large deletion (containing many ribosomal RNAs and tRNAs genes) and a mutation of DNA polymerase (one of the 11 mutations) critically contributed to this thermotolerance. The relationship between the phenotypic changes and the gene mutations are discussed, comparing with another thermally adapted A. pasteurianus strains obtained previously.