Abstract:
In order to construct a food-safe strain that could produce glycolate, the metabolic modification of
Bacillus subtilis was carried out. In this study, the exogenous isocitrate lyase gene (
aceA) was first integrated into the genome of
Bacillus subtilis by homologous recombination, and the starting strain 164MCT-GA was constructed. Then the glycolate anabolism was optimized by means of metabolic engineering in the starting strain 164MCT-GA. The results showed that 164MCT-GA could synthesize glycolate with glycerol as substrate, and the yield of shaker fermentation was 0.114 g/L. To increase the supply of the key intermediate substrates, the citrate synthase gene (
citA) and the glyoxylate reductase gene (
yvcT) were overexpressed by replacing the native promoter with individual T7 promoter. The
Bacillus strains were further engineered at multiple loci that included lactate dehydrogenase (
ldh), phosphate acetyltransferase (
pta) and acetyl-CoA transacetylase (
mmgA,
yhfs), in an attempt to modulate the carbon flux toward the formation of glycolate with a higher efficiency. The fermentation study revealed that the accumulated concentration of glycolate from the obtained
B. subtilis strain GA3-52 reached 0.572 g/L, with a conversion rate of 0.175 g/g glycerol, the titer was more than five times as much as that achieved by 164MCT-GA. Thus, this study constructed a de novo synthesis pathway in
B. subtilis, and laid the foundation for the fermentation production of high yield glycolic acid by food safety bacteria.