Semi-continuous fermentation of a thermotolerant and high acetic acid producing Acetobacter pasteurianus bacterium

Among 63 strains isolated from fruits and homemade vinegars from different ecosystems of Morocco, a thermotolerant bacterium with high production of acetic acid was selected and evaluated for its ability to perform efficient acetous fermentation at high temperature in a bioreactor. CV01 strain, isolated from cactus (Opuntia ficus-indica), was considered to be an Acetobacter pasteurianus sp. according to phylogenetic study based on 16s rDNA gene sequence analysis. An optimal culture medium containing initial concentrations of acetic acid and ethanol of 1% (v/v) and 4% (v/v), respectively, was used. The growth kinetics of this isolate were monitored in flasks and compared with those of the wild type LMG 1625 mesophilic strain and the thermoresistant Acetobacter senegalensis reference strain. The CV01 strain exhibited abundant growth along with high amount of produced acetic acid at high temperature (41°C). Subsequently, a 20-L stirred tank bioreactor was used to assess thermotolerance and acidoresistance properties of the selected strain during semi-continuous acetic acid fermentation at 38°C. Interestingly, a total amount of 13.4% (w/v) acetic acid was yielded at the end of fermentation. Moreover, this bacterium could produce during the same fermentation process a final concentration of 11.2 g/L gluconic acid, a sensory quality indicator in vinegar production. Finally, the enzymatic study showed that CV01 strain exhibited high ADH and ALDH enzyme activity at 38°C compared with the mesophilic reference strain LMG 1632, which was significantly susceptible to thermal inactivation.