Cometabolism of w-phenylalkanoic acids with butyric acid for efficient production of aromatic polyesters in Pseudomonas putida BM01

Abstract

Poly(3-hydroxy-5-phenylvalerate) [P(3HPV)] was efficiently accumulated from 5-phenylvalerate (5PV) in Pseudomonas putida BM01 in a mineral salts medium containing butyric acid (BA) as the cosubstrate. A novel aromatic copolyester, poly(5 mol% 3-hydroxy-4-phenylbutyrate co- 95 mol% 3-hydroxy-6-phenylhexanoate) [P(3HPB-co-3HPC)] was also synthesized from 6-phenylhexanoate (6PC) plus BA. The two aromatic polymers, P(3HPV) and P(3HPB-co-3HPC), were found to be amorphous and showed different glass-transition temperatures at 15°C and 10°C, respectively. When the bacterium was grown in a medium containing 20 mM 5PV as the sole carbon source for 140 h, 0.4 g/l of dry cells was obtained in a flask cultivation and 20 wt% of P(3HPV) homopolymer was accumulated in the cells. However, when it was grown with a mixture of 2 mM 5PV and 50 mM BA for 40 h, the yield of dry biomass was increased up to 25 g/l and the content of P(3HPV) in the dry cells was optimally 56 wt%. This efficient production of P(3HPV) homopolymer from the mixed substrate was feasible because BA only supported cell growth and did not induce any aliphatic PHA accumulation. The metabolites released into the PHA synthesis medium were analyzed using GC or GC/ MS. Two β-oxidation derivatives, 3-phenylpropionic acid and trans-cinnamic acid, were found in the 5PV-grown cell medium and these comprised 55-88 mol% of the 5PV consumed. In the 6PC-grown medium containing BA, seven β-oxidation and related intermediates were found, which included phenylacetic acid, 4-phenylbutyric acid, cis-4-phenyl-2-butenoic acid, trans-4-phenyl-3-butenoic acid, trans-4-phenyl-2-butenoic acid, 3-hydroxy-4-phenylbutyric acid, and 3-hydroxy-6-phenylhexanoic acid. Accordingly, based on the metabolite analysis, PHA synthesis pathways from the two aromatic carbon sources are suggested.