Direct production of L-lysine from raw corn starch by Corynebacterium glutamicum secreting Streptococcus bovis α-amylase using cspB promoter and signal sequence

Corynebacterium glutamicum is an important microorganism in the industrial production of amino acids. We engineered a strain of C. glutamicum that secretes alpha-amylase from Streptococcus bovis 148 (AmyA) for the efficient utilization of raw starch. Among the promoters and signal sequences tested, those of cspB from C. glutamicum possessed the highest expression level. The fusion gene was introduced into the homoserine dehydrogenase gene locus on the chromosome by homologous recombination. L-Lysine fermentation was conducted using C. glutamicum secreting AmyA in the growth medium containing 50 g/l of raw corn starch as the sole carbon source at various temperatures in the range 30 to 40 degrees C. Efficient L-lysine production and raw starch degradation were achieved at 34 and 37 degrees C, respectively. The alpha-amylase activity using raw corn starch was more than 2.5 times higher than that using glucose as the sole carbon source during L-lysine fermentation. AmyA expression under the control of cspB promoter was assumed to be induced when raw starch was used as the sole carbon source. These results indicate that efficient simultaneous saccharification and fermentation of raw corn starch to L-lysine were achieved by C. glutamicum secreting AmyA using the cspB promoter and signal sequence.