Screening Thermo- and Ethanol Tolerant Bacteria for Ethanol Fermentation

Abstract

The thermophilic bacteria receive considerably interest nowadays because of a current challenge of increasing global temperature. Particularly for ethanol production, the thermo-ethanologenic bacteria possess advantages due to lower contamination risk, cost saving in industrial scale, and the wide range of sugars utilization. In this study, 13 bacterial isolates obtained from the previous isolation study were tested for their fermentative capacity and ethanol tolerance at high temperatures. Five bacterial isolates HM2, M2, MC3, MR1 and RD were found to be tolerant up to 12% ethanol. Of which HM2, M2 and MR1 could ferment glucose well at 30, 35 and 40°C, particularly isolates HM2 and MR1 could perform the fermentative capacity at 45°C and even 50°C. In the presence of 12, 16, and 20% w/v glucose, isolates HM2, M2, and MR1 showed the high fermentation rate by giving high gas production; however, the rate slightly decreased in the presence of 24% w/v glucose. The fermentative performance by these three isolates could happen at different pH levels of 4.0, 5.0 and 6.0. The favourable conditions of ethanol fermentation were found at 18.5% glucose, pH 5.0, and 33°C for isolate HM2 and at 14% glucose, pH 5.5, and 40°C for isolate MR1. The results of sequencing analysis of partial 16S rRNA gene showed that the gene sequences of the selected isolate HM2 shared 99% similarity with Bacillus subtilis.