Enhanced production of poly(lactate- co-3-hydroxybutyrate) from xylose in engineered Escherichia coli overexpressing a galactitol transporter.

Nduko, John; Matsumoto, Ken'ichiro; Ooi, Toshihiko; Taguchi, Seiichi

Poly(lactate- co-3-hydroxybutyrate) (P(LA- co-3HB)) was previously produced from xylose in engineered Escherichia coli. The aim of this study was to increase the polymer productivity and LA fraction in P(LA- co-3HB) using two metabolic engineering approaches: (1) deletions of competing pathways to lactate production and (2) overexpression of a galactitol transporter (GatC), which contributes to the ATP-independent xylose uptake. Engineered E. coli mutants (Δ pflA, Δ pta, Δ ackA, Δ poxB, Δ dld, and a dual mutant; Δ pflA + Δ dld) and their parent strain, BW25113, were grown on 20 g l xylose for P(LA- co-3HB) production. The single deletions of Δ pflA, Δ pta, and Δ dld increased the LA fraction (58-66 mol%) compared to BW25113 (56 mol%). In particular, the Δ pflA + Δ dld strain produced P(LA- co-3HB) containing 73 mol% LA. Furthermore, GatC overexpression increased both polymer yields and LA fractions in Δ pflA, Δ pta, and Δ dld mutants, and BW25113. The Δ pflA + gatC strain achieved a productivity of 8.3 g l, which was 72 % of the theoretical maximum yield. Thus, to eliminate limitation of the carbon source, higher concentration of xylose was fed. As a result, BW25113 harboring gatC grown on 40 g l xylose reached the highest P(LA- co-3HB) productivity of 14.4 g l. On the other hand, the Δ pflA + Δ dld strain grown on 30 g l xylose synthesized 6.4 g l P(LA- co-3HB) while maintaining the highest LA fraction (73 mol%). The results indicated the usefulness of GatC for enhanced production of P(LA- co-3HB) from xylose, and the gene deletions to upregulate the LA fraction in P(LA- co-3HB). The polymers obtained had weight-averaged molecular weights in the range of 34,000-114,000.

XYLOSE; ALDOSES; ESCHERICHIA coli; LIGNOCELLULOSE; BIOMASS; POLYMER research

Applied Microbiology & Biotechnology, 2014, Vol 98, Issue 6, p2453

0175-7598

Academic Journal

10.1007/s00253-013-5401-0