Strategies to reduce the culture medium costs for a high-yield and high-selectivity bio-based 2,3-butanediol production

Bio-based 2,3-butanediol (2,3-BDO) production on a large scale depends on critical factors, such as culture medium, oxygen supply, pH and biosafety. In this study, three strategies for reducing culture medium costs were investigated: carbon/nitrogen (C/N) ratio; low-cost nitrogen sources (crude yeast extract, brewer's yeast extract, corn steep liquor, urea, sodium nitrate, ammonium chloride, ammonium sulfate and dibasic ammonium phosphate); and microbial pH autoregulation. Batch fermentations were performed in a microaerobic environment using wild-type and safe Paenibacillus peoriae NRRL BD 62. The yield and selectivity of 2,3-BDO were used as control variables. A ratio between 2,3-BDO production and glucose consumption (Y_P/S) of almost 80% and an optical purity of 87% levo-2,3-BDO, with no acetoin accumulation, were achieved in an NH₄Cl-based medium at C/N = 8.5 g/g and without external pH control, considering an initial glucose of 10 g/L. Based on Free on Board prices, a 63% savings in culture medium costs was achieved by replacing commercial yeast extract at pH 5. Validation assays with higher initial glucose concentrations showed a Y_P/S of 0.40 g/g and an optical levo-/meso-2,3-BDO ratio of 1:0.8, with negligible acetoin accumulation. Therefore, the NH₄Cl-based medium at C/N = 8.5 g/g and without pH control was considered economically promising for high-yield and high-selectivity bio-based 2,3-BDO production.