| As 1,3-propanediol?1,3-PDO?is widely used in industry,especially as a monomer of new synthetic fiber material,polytrimethylene-tereph-thalate?PTT?.The global demand for 1,3-PDO is increasing year by year.Producing 1,3-PDO by biological fermentation is more suitable than conventional chemical systhesis,because of low energy consumption and more environmentally friendly.In this work,the D-ldhA gene of Lactobacillus brevis was knocked out by homologous recombination in order to reduce the yield of lactic acid,a by-product of L.brevis in producing1,3-PDO,and to improve the yield of 1,3-PDO and the conversion rate of glycerol.The lactate dehydrogenase?ldh?activity of the engineered L.brevis was 30.8 U/mL at 24 h,34.7%less than that of original strain.When fermentation using the engineered strain with 2%glucose and 2%glycerol,10.07 g/L of lactic acid was produced at 48 h,which was 25.8%less than that of the original strain.The yield of 1,3-PDO and the conversion of glycerol were 13.26 g/L and 0.78mol/mol,respectively,which were 33.33%and 19.2%increased when compared with those of the original strain.In order to improve the yield and conversion rate of 1,3-PDO further,the fermentation carbon and nitrogen sources were optimized for the engineered strain.The results showed that glucose or fructose were the best co-carbon source in glycerol fermentation.The mixture of yeast extract and peptone at equal amount was the best nitrogen source.The highest yield of 1,3-PDO was obtained when 20 g/L glycerol and glucose were used at the ratio of 1:1.Under the optimal conditions,the maximum yield of 1,3-PDO and glycerol conversion rate were 16.43 g/L and 0.83mol/mol,respectively.Fed-batch fermentation was employed to further improve the yield of 1,3-PDO.The maximum yield of 1,3-PDO reached 28.19 g/L,the glycerol conversion rate was 0.87 mol/mol at48 h,and the production efficiency was 0.59 g·L-1·h-1.The maximum yield of by-products,i.e.lactic acid and acetic acid,were 13.44 g/L and 12.75 g/L respectively. |
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