Production of L-lactic acid from pentose by a genetically engineered Escherichia coli

Abstract:

Abstract:［Objective］In this study，we constructed a recombinant Escherichia coli strain for the production of high-purity L-lactic acid，using a homoethanol fermenting mutant E．coli SZ470 (ΔfrdBC ΔldhA ΔackA ΔfocA-pB ΔpdhR::pBp6-pBrbs-aceEF-lpd) as the starting strain． ［Methods］By using homologous recombination，we deleted the adhE gene from SZ470 to obtain a mutant Escherichia coli JH01，which could not grow under anaerobic conditions． Then we cloned the Llactate dehydrogenase gene (ldhL) of Pediococcus acidilactici and inserted it into the chromosome of JH01 via electroporation to obtain a recombinant strain Escherichia coli JH12． We evaluated the L-lactic acid production of the recombinant strain in a 15 L fermenter．［Results］In 10 L LB medium supplemented with 6% glucose，JH12 maintained maximal cell growth and an efficient L-lactic acid production rate for 36 h． Glucose consumption rate achieved was 1.46 g/(L·h) and L-lactic acid production rate was 1. 14 g/(L·h)．The results also show that 41.13 g/L lactic acid was produced，achieving a purity of 95.69% (based on total fermentation products) ．Xylose consumption rate was 0.88 g/(L·h) and L-lactic acid production rate was 0.60 g/(L·h)．The production of lactic acid was 34.73 g/L， achieving a purity of 98%．There were no succinic acid and formic acid detected and only little amount of acetic acid generated during the fermentation．［Conclusion］ We constructed a homolactic acid fermentation strain E． coli JH12，which could efficiently convert glucose and xylose into high-purity L-lactic acid． JH12 could have great potential in industrial fermentation for L-lactic acid production．