Abstract
Lactate and isoprene are two common monomers for the industrial production of polyesters and synthetic rubbers. The present study tested the co-production of D-lactate and isoprene by engineered Escherichia coli in microaerobic conditions. The deletion of alcohol dehydrogenase (adhE) and acetate kinase (ackA) genes, along with the supplementation with betaine, improved the co-production of lactate and isoprene from the substrates of glucose and mevalonate. In fed-batch studies, microaerobic fermentation significantly improved the isoprene concentration in fermentation outlet gas (average 0.021 g/L), compared with fermentation under aerobic conditions (average 0.0009 g/L). The final production of D-lactate and isoprene can reach 44.0 g/L and 3.2 g/L, respectively, through fed-batch microaerobic fermentation. Our study demonstrated a dual-phase production strategy in the co-production of isoprene (gas phase) and lactate (liquid phase). The increased concentration of gas-phase isoprene could benefit the downstream process and decrease the production cost to collect and purify the bio-isoprene from the fermentation outlet gas. The proposed microaerobic process can potentially be applied in the production of other volatile bioproducts to benefit the downstream purification process.
Highlights
With respect to the exhaustion of fossil fuels and increasing environmental issues, biopolymers have recently been developed as alternatives to fossil-fuel-derived synthetic polymers
The results demonstrate that the deletion of alcohol dehydrogenase (adhE) and acetate kinase (ackA) can reduce the production The results demonstrate that the deletion of adhE and ackA can reduce the production of ethanol/acetate and improve the production of lactate by the isoprene‐producing strain of ethanol/acetate improve theshown production of lactate‐producing lactate by the isoprene-producing
The plasmids of pYJM4 and pYJM16 were constructed in a previous study [21]. pYJM4 carries the gene of isoprene synthase (IspS). pYJM16 carries four genes of the downstream process of the MVA pathway: mevalonate-5-kinase (MVK), mevalonate-3-phosphate-5-kinase (PMK), mevalonate-5-pyrophosphate decarboxylase (MVD), and isopentenyl pyrophosphate isomerase (IDI) from Saccharomyces cerevisiae (Table 1)
Summary
With respect to the exhaustion of fossil fuels and increasing environmental issues, biopolymers have recently been developed as alternatives to fossil-fuel-derived synthetic polymers. Engineered E. coli strains have been utilized in the biosynthesis of isoprene through the mevalonate (MVA) or 1-deoxy-D-xylulose-5-phosphate (DXP) pathways [8]. The low concentration of bio-isoprene produced in the aerobic tractive distillation process [2]. During process,the thepresence presenceofofisoprene isoprene and lactic acid in dual phases. Lactic acid in dual phases (isoprene in broth) broth)could couldachieve achievetechnical technical and economic benefits for the Dehydrogenase; lpd: lipoamide dehydrogenase; adhE: alcohol/aldehyde dehydrogenase; pta: phosphate acetyltransferase; transferase; ackA: acetate kinase. Cell, theinlactic acid and were produced using the substrates of glucose and mevalonate, tively, dual phase and isoprene under microaerobic fermentation conditions.
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