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Isolation of the Acetic Acid Bacteria From Home-Made Vinegars and Evaluation of Thermal Tolerance
Using thermotolerant strains of acetobacteraceae plays a much important role in bioconversion of alcohols to aldehydes and acids.
Looking for such acetate producing strains, in an attempt 70 samples of traditionally home-made vinegars were collected from 4 districts of country. The regions include Tehran, Takestan, Qazvin, and Abhar cities. Acetate producing strains were isolated and sorted according to their age and the region isolated from. According to interactions between age and region most of the strains were isolated from Takestan samples of 8 to 12 months old. Among the 39 isolates, 23 strains were tentatively identified as Acetobacter spp. (not differentiated from Gluconoacetobacter sp.) and the 16 remaining strains as Gluconobacter spp.. Because half of the Gluconobacter strains had an unusual capacity of acetate oxidation in “ethanol oxidation medium” (the special trait of thermotolerant gluconobacter), “lactate oxidation” was referenced as the sole test to differentiate members of to genera. While the optimum growth temperature of these acetate producing bacteria varies between 30°C to 33°C, and the maximum growth temperature is less than 37°C, but one-third of isolates were able to grow at 40±1°C. These isolates were assumed as thermotolerant strains. Thus it seems that thermotolerancy of the acetate producing bacteria more or less is a frequent feature among natural microbiota of domestic home-made vinegar in our country. These data are much different from that of other Asian countries such as Japan, and the climate effects may be the main reason. This is an industrially important trait, because the producing strains can easily resist the seasonal heat fluctuations.