Production of L-Lysine from starch by Corynebacterium glutamicum displaying alpha-amylase on its cell surface

We engineered a Corynebacterium glutamicum strain displaying alpha-amylase from Streptococcus bovis 148 (AmyA) on its cell surface to produce amino acids directly from starch. We used PgsA from Bacillus subtilis as an anchor protein, and the N-terminus of alpha-amylase was fused to the PgsA. The genes of the fusion protein were integrated into the homoserine dehydrogenase gene locus on the chromosome by homologous recombination. L-Lysine fermentation was carried out using C. glutamicum displaying AmyA in the growth medium containing 50 g/l soluble starch as the sole carbon source. We performed L-lysine fermentation at various temperatures (30-40 degrees C) and pHs (6.0-7.0), as the optimal temperatures and pHs of AmyA and C. glutamicum differ significantly. The highest L-lysine yield was recorded at 30 degrees C and pH 7.0. The amount of soluble starch was reduced to 18.29 g/l, and 6.04 g/l L-lysine was produced in 24 h. The L-lysine yield obtained using soluble starch as the sole carbon source was higher than that using glucose as the sole carbon source after 24 h when the same amount of substrates was added. The results shown in the current study demonstrate that C. glutamicum displaying alpha-amylase has a potential to directly convert soluble starch to amino acids.