By applying non-sterile open fermentation of food waste, various thermotolerant L-lactic acid-producing bacteria were isolated and identified. The predominant bacterial isolates showing higher accumulation of L-lactic acid belong to 3 groups of Bacillus coagulans, according to their 16S rRNA gene sequence similarities. B. coagulans strains M21 and M36 produced high amounts of L-lactic acid of high optical purity and lactic acid selectivity in model kitchen refuse medium and glucose-yeast extract-peptone medium. Other thermotolerant isolates resembling to Bacillus humi, B. runs, B. subtilis, B. niacini and B. soli were also identified. These bacteria produced low amounts of L-lactic acid of more than 99% optical purity. All isolated strains showed the highest growth rate at temperatures around 55-60 degrees C. They showed unique responses to various oxygen supply conditions. The majority of isolates produced L-lactic acid at a low overall oxygen transfer coefficient (K(L)a); however, acetic acid was produced instead of L-lactic acid at a high K(L)a. B. coagulans M21 was the only strain that produced high, consistent, and reproducible amounts of optically pure L-lactic acid (>99% optical purity) under high and low K(L)a conditions in a homo-fermentative manner. (C) 2013, The Society for Biotechnology, Japan. All rights reserved.