ABSTRACT
Aims: The objective of this research was to isolate and identify lactic acid producing bacteria from soils and tree barks in Thailand. Their acid production was also determined. Methodology and results: Eleven bacterial strains isolated from soils and tree barks were screened for their lactic acid production. They were divided into 4 groups based on their phenotypic characteristics and 16S rRNA gene sequence analyses. Group I (3 isolates) identified as Lactococcus produced L-lactic acid ranged from 72.32 ± 0.707-77.47 ± 0.184 g/L, yield of 0.96 ± 0.011-1.06 ± 0.008 g/g, productivity of 1.00 ± 0.010-1.08 ± 0.003 g/L.h and optical purity was 100%. Group II (3 isolates) identified as Enterococcus hirae, produced L-lactic acid ranged from 31.56 ± 0.424-34.86 ± 0.283 g/L, yield of 1.06 ± 0.008-1.23 ± 0.036 g/g, productivity of 0.44 ± 0.006-0.48 ± 0.004 g/L.h and optical purity was 98.6- 100%. Group III (3 isolates) identified as Bacillus coagulans, produced L-lactic acid ranged from 48.48 ± 0.283-93.51 ± 0.552 g/L, yield of 1.00 ± 0.001-1.07 ± 0.005 g/g, productivity of 0.67 ± 0.004-1.30 ± 0.008 g/L.h and high optical purity of the tested isolate was 99.56%. Group IV (2 isolates) identified as Sporoactobacillus. Only NN2 produced D-lactic acid concentration 87.64 ± 0.375 g/L, yield of 0.83 ± 0.000 g/g, productivity of 1.22 ± 0.005 g/L.h and optical purity was 96.16%. All isolates produced lactic acid when 120 g/L of the initial glucose was used as a substrate. Conclusion, significance and impact of study: Lactic acid producing bacteria are isolated from soils and tree barks. The coccal isolates could produce high L-lactic acid concentration with high optical purity while the spore-forming isolates produces L- and D-lactic acid which are useful for food preservation, chemical in pharmaceutical, cosmetic and textile industries.