Malate Supplementation Enhances the Growth and Sporulation Efficiency of Bacillus subtilis DF

To improve the growth and sporulation efficiency of Bacillus subtilis, the effect of malate on the cell growth and metabolism of B. subtilis DF was investigated in a 30 L bioreactor. At 22 h of fermentation, a biomass of 3.68 × 1010 CFU/mL was obtained by malate addition to a final concentration of 1.5% during 16–27 h after the pH reached 8.0 at 16 h, which was 71.9% higher than that of the control group. Meanwhile, the number of spores was 3.63 × 1010 CFU/mL, which was 92.1% higher than that of the control group. Differential transcriptomic analysis showed that malate increased the metabolic efficiency of the gluconeogenesis and pentose phosphate pathways with 1.38 to 2.51-fold up-regulation of the zwf, pckA and fbaA genes, respectively and the metabolic efficiency of the tricarboxylic acid (TCA) cycle with 3.10-fold up-regulation of the citZ gene, reduced cellular oxidative stress with a 72.9% down-regulation of the poxL gene, a 3.88-fold up-regulation of the trxA gene, and thus a 45.9%–51.3% reduction in H2O2 concentration during 19–24 h, and enhanced the phosphorylation efficiency of Spo0A with down-regulation of the kipL, rapAD and abrB genes by 57.5%–75.9%, and up-regulation of the clpX, phrCF, spo0B and sigA genes by 1.73–13.76 folds, significantly improving the growth and sporulation efficiency of B. subtilis DF. These findings provide theoretical supports for the industrial application of B. subtilis.