No abstract

A thermophilic strain, No. 1023, of Acetobacter aceti was isolated, by which it became possible to carry out submerged vinegar production at 35°C. The thermophilic property of the strain correlated closely with its acetic acid resistance. Strain No. 1023 lost acetic acid resistance at high frequency (more than 55% in isolated strains) and lost ethanol oxidizing ability at lower frequency (about 40%) compared to the above in the stationary growth phase in a liquid mediumcontaining ethanol. The loss of these properties during the stationary phase was confirmed using a genetically marked strain {pro") of No. 1023. Such frequent loss of acetic acid resistance and ethanol oxidizing ability suggested a relationship between these properties and a plasmid. A plasmid, PTA5001, was found in strain No. 1023, and its molecular weight was determined to be 17x 106 daltons by electron microscopy. The plasmid, however, seemedto have no direct connection with acetic acid resistance or ethanol oxidizing ability, because the same plasmid was found in all strains which had no these properties.

Industrial vinegar production by submerged acetic acid fermentation has been carried out using Acetobacter strains at about 30°C. To obtain strains suitable for acetic acid fermentation at higher temperature, about 1,100 strains of acetic acid bacteria were isolated from vinegar mash, soils in vinegar factories and fruits, and their activities to oxidize ethanol at high temperature were examined. One of these strains, No. 1023, identified as Acetobacter aceti, retained full activity to produce acetic acid in continuous submerged culture at 35°C and produced 45 % of activity at 38°C, while the usual strain of A. aceti completely lost its activity at 35°C. Thus the use of this strain may reduce the cooling costs of industrial vinegar production.