Molecular Taxonomy of Acetobacter syzygii SKU19 and Characterization of Its Acetic Acid Adapted Strains

Abstract

Acetobacter species are one of the most suitable bacteria for the proteomic analysis of proteins involved in stress response or adaptation. Among 129 isolates of thermotolerant acetic-acid bacteria, two isolates SKU19 and SKU123 were selected as an acetic-acid sensitive and acetic-acid resistant
strain, respectively. Molecular taxonomy of these isolates indicated that SKU19 and SKU123 were Acetobacter syzygii and A. pasteurianus, respectively. To elucidate an adaptive response to acetic acid, acetic-acid-adapted strains were isolated from sequential cultivations of the acetic-acid sensitive strain, A. syzygii SKU19, in a medium containing 1% acetic acid. The adapted variants could be divided into two groups based on their growth and ability to further oxidize acetate. The first group consisted of cells with increased overoxidation (rapid acetate oxidizers), while the second group contained cells with increased stability to acetate (slow acetate oxidizers). The membrane-bound quinoprotein alcohol dehydrogenase (PQQ-ADH) and aldehyde dehydrogenase (ALDH) activities of these adapted strains were higher than those of the wild type. The result corresponded well with the increased amount of protein with a molecular mass of 72-80 (subunit I) and 44-54 kDa (subunit II) when the organism was cultivated in a medium containing acetic acid. This study confirmed that acetic-acid resistance in aceticacid bacteria is conferred by several mechanisms, such as acetate assimilation and PQQ-ADH functions.