Evaluation of Thermotolerance of Native Strains of Acetic acid Bacteria in Iran

ABSTRACT: Native strains of acetic acid bacteria were isolated from a collection of domestic vinegars of four cities with somehow different climates. From 70 vinegar samples, 39 isolates of acetic acid bacteria were finally obtained. Identification of the isolates was performed to the genus level. All isolates were screened for growing at 37 and 40 °C. One third of isolates were able to grow at 40 °C. Sixty percent of thermotolerant strains were isolated from a city has 2 °C higher annual temperature average. One of isolates that was able to grow at 40°C and also was rather able to produce a considerable amount of acetic acid was called Acetobacter sp. strain53. It was grown in optimized condition, i.e., pH 4, at 33 ?C, and 150 rpm. The results showed that the strain 53 was able to produce the most amount of acetic acid within this condition (40 g/l). Furthermore, it could produce acetic acid even when acetic acid was added in 4% initial concentration. It also oxidized higher concentration of ethanol up to 9% without any appreciable lag time. Finally measurement of activity of ADH showed that ADH in thermotolerant strain 53 is active in a wide range of temperature variations up to 60 °C. By having these specific characterizations, thermotolerant acetic acid bacteria are useful for vinegar fermentation at higher temperature, which may reduce cooling costs.