Efficient Production of Optically Pure d -Lactic Acid from Raw Corn Starch by Using a Genetically Modified l -Lactate Dehydrogenase Gene-Deficient and α-Amylase-Secreting Lactobacillus plantarum Strain

Abstract

ABSTRACT In order to achieve direct and efficient fermentation of optically pure d -lactic acid from raw corn starch, we constructed l -lactate dehydrogenase gene ( ldhL1 )-deficient Lactobacillus plantarum and introduced a plasmid encoding Streptococcus bovis 148 α-amylase (AmyA). The resulting strain produced only d -lactic acid from glucose and successfully expressed amyA . With the aid of secreting AmyA, direct d -lactic acid fermentation from raw corn starch was accomplished. After 48 h of fermentation, 73.2 g/liter of lactic acid was produced with a high yield (0.85 g per g of consumed sugar) and an optical purity of 99.6%. Moreover, a strain replacing the ldhL1 gene with an amyA -secreting expression cassette was constructed. Using this strain, direct d -lactic acid fermentation from raw corn starch was accomplished in the absence of selective pressure by antibiotics. This is the first report of direct d -lactic acid fermentation from raw starch.