Abstract
Objective
A bio-based process is appealing for purification of l-lactic acid, the major enantiomer of polylactic acid syrup, generated by thermochemical processes at the end of life of PLA-based plastics, from its chiral impurity, d-lactic acid, before reuse.
Results
Polylactic acid (PLA), a renewable alternative to petroleum-derived plastics, contains a mixture of l- and d-lactic acid (LA) isomers with the l-isomer dominating (up to 95 %). A novel bio-based process was developed to produce chirally pure l-LA from syrup produced during recycling of PLA-plastics. This process utilizes an engineered Escherichia coli (strain DC1001) containing novel gene deletions (lld, ykg) that eliminated the oxidative metabolism of l-lactate, leaving the membrane-bound d-lactate dehydrogenases to selectively metabolize the d-isomer. Strain DC1001 removed 8.7 g d-lactate l−1 from a PLA-syrup containing 135 g total lactic acid l−1 in 24 h. Average rates of removal of d-lactic acid were 0.25 g d-lactate h−1 (g cell dry weight)−1 and 0.36 g d-lactate l−1 h−1.
Conclusion
Bio-based purification of PLA-syrup utilizing E. coli strain DC1001 is an attractive process step during recycling of PLA-plastics. This selective oxidation process can also be used to remove chiral contamination of l-lactate in medical applications.
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Acknowledgments
This work was supported by grants from the U.S. Department of Agriculture (USDA) (2012-67009-19596; LOI) and Biomass Research and Development Initiative Competitive Grant (2011-10006-30358) from the USDA National Institute of Food and Agriculture. This work was also supported by funding from the U.S. Department of Energy’s Office of Energy Efficiency and Renewable Energy, Bioenergy Technologies Office and sponsored by the U.S. Department of Energy’s International Affairs under award number, DE-PI0000031, BASF and the Florida Department of Agriculture and Consumer Services.
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Chauliac, D., Pullammanappallil, P.C., Ingram, L.O. et al. Removing chiral contamination of lactate solutions by selective metabolism of the d-enantiomer. Biotechnol Lett 37, 2411–2418 (2015). https://doi.org/10.1007/s10529-015-1924-z
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DOI: https://doi.org/10.1007/s10529-015-1924-z