POTENTIAL MICROORGANISM FOR THE DIRECT PRODUCTION OF L-LACTIC ACID FROM CASSAVA STARCH WITHOUT CARBON DIOXIDE PRODUCTION

抄録

The application of a starch-utilizing and homofermentative microorganism will be of great benefit to the lactate production industry as well as the protection of carbon dioxide production and accumulation in human surrounding environment. A homolactic bacterium isolated from the cassava starch waste sample in Nakhon Ratchasima Province, Thailand, could actively convert cassava polysaccharides to L-lactic acid. The isolate produced the maximum amount of lactic acid of about 9 g/l in the suitable medium containing 2% cassava starch in laboratory scale. The gene encoding lactate dehydrogenase, a key enzyme in lactic acid fermentation by most lactic acid bacteria, of the microorganism was detected. The nucleotide sequence of the gene was analysed. To enhance the lactic acid production from cassava starch, the starch-utilizing strain was improved by exposing to two mutagens: Ultraviolet (UV) light and N-Methyl-N'-Nitro-N-Nitrosoguanidine (MNNG). A mutant obtained from UV-UV-MNNG treatments could produce lactic acid at approximate ten percents higher than its original strain. The strain was inally selected and maintained for using as the potential microorganism for the direct production of lactic acid from cassava starch without carbon dioxide production. After subculturing the culture for sixth times, the mutant could still produce the similar amount of lactic acid as before the first subculture.