Removing chiral contamination of lactate solutions by selective metabolism of the D-enantiomer.
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).


CONCLUSIONS
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.
Department of Microbiology and Cell Science, IFAS, University of Florida, Gainesville, FL, 32611, USA. d.chauliac@ufl.edu.
Diane
D
Chauliac
Department of Agricultural and Biological Engineering, IFAS, University of Florida, Gainesville, FL, 32611, USA. pcpratap@ufl.edu.
P C
PC
Pullammanappallil
Department of Microbiology and Cell Science, IFAS, University of Florida, Gainesville, FL, 32611, USA. ingram@ufl.edu.
L O
LO
Ingram
Department of Microbiology and Cell Science, IFAS, University of Florida, Gainesville, FL, 32611, USA. shan@ufl.edu.
K T
KT
Shanmugam
D004926:Escherichia coli / Q000235:genetics* / Q000378:metabolism*; D017353:Gene Deletion; D019344:Lactic Acid / Q000737:chemistry / Q000302:isolation & purification* / Q000378:metabolism; D060847:Metabolic Engineering; D053858:Metabolic Networks and Pathways / Q000235:genetics; D011091:Polyesters; D011108:Polymers / Q000737:chemistry* / Q000378:metabolism*; D012996:Solutions; D013237:Stereoisomerism
D011091:Polyesters; D011108:Polymers; D012996:Solutions; D019344:Lactic Acid; C033616:poly(lactide)
D-Lactic acid metabolism; Escherichia coli; L-Lactate dehydrogenase; Polylactic acid recycling; Purification of PLA-syrup