Isolation and study of thermotolerant Bacillus strains including L-lactic acid production from kitchen refuse

Abstract

Seven thermotolerant, lactic acid-producing bacteria were isolated from tapioca factory waste and, liquid and solid organic composts in the northeastern Thailand. They were able to grow at temperatures ranging from 30 to 60oC, with maximum growth observed at approximately 42 oC, and within a pH ranging of 5.2 to 7.5, with maximum growth observed at approximately pH 6.5. These bacteria were identified as the genus Bacillus based on their phenotypic characteristics. The fermentation of saccharified kitchen refuse by these strains was also evaluated. Using glucoamylase-pretreated model kitchen refuse as a substrate medium, all seven strains produced L-lactic acid (15.12-24.07 g/l). Among the seven strains tested, strain N15 produced the largest amount of L-lactic acid (24.07 g/l), achieving a 149.3% yield from glucose, 144.9% yield from total sugar, 97% optical activity, 95.5% lactic acid selectivity and 0.31 g/l/h L-lactic acid productivity. By using 16S rDNA sequence analysis, strain N15 displayed 99.45% homology to Bacillus coagulans.