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Open Access Research

Efficient synthesis of L-lactic acid from glycerol by metabolically engineered Escherichia coli

Suman Mazumdar1, Matthew D Blankschien1, James M Clomburg1 and Ramon Gonzalez12*

Author Affiliations

1 Department of Chemical and Biomolecular Engineering, Rice University, 6100 Main Street, MS-362, Houston, TX 77005, USA

2 Department of Bioengineering, Rice University, Houston TX, USA

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Microbial Cell Factories 2013, 12:7  doi:10.1186/1475-2859-12-7

Published: 25 January 2013

Abstract

Background

Due to its abundance and low-price, glycerol has become an attractive carbon source for the industrial production of value-added fuels and chemicals. This work reports the engineering of E. coli for the efficient conversion of glycerol into L-lactic acid (L-lactate).

Results

Escherichia coli strains have previously been metabolically engineered for the microaerobic production of D-lactic acid from glycerol in defined media by disrupting genes that minimize the synthesis of succinate, acetate, and ethanol, and also overexpressing the respiratory route of glycerol dissimilation (GlpK/GlpD). Here, further rounds of rationale design were performed on these strains for the homofermentative production of L-lactate, not normally produced in E. coli. Specifically, L-lactate production was enabled by: 1), replacing the native D-lactate specific dehydrogenase with Streptococcus bovis L-lactate dehydrogenase (L-LDH), 2) blocking the methylglyoxal bypass pathways to avoid the synthesis of a racemic mixture of D- and L-lactate and prevent the accumulation of toxic intermediate, methylglyoxal, and 3) the native aerobic L-lactate dehydrogenase was blocked to prevent the undesired utilization of L-lactate. The engineered strain produced 50 g/L of L-lactate from 56 g/L of crude glycerol at a yield 93% of the theoretical maximum and with high optical (99.9%) and chemical (97%) purity.

Conclusions

This study demonstrates the efficient conversion of glycerol to L-lactate, a microbial process that had not been reported in the literature prior to our work. The engineered biocatalysts produced L-lactate from crude glycerol in defined minimal salts medium at high chemical and optical purity.

Keywords:
L-lactic acid; Glycerol; Metabolic engineering; Escherichia coli