Biosynthesis of copolyesters by Hydrogenophaga pseudoflava from various lactones

Abstract

Hydrogenophaga pseudoflava (formerly Pseudomonas pseudoflava) was able to accumulate a large amount of copolyesters when grown on mixed substrates of glucose and lactones in a batch fermentation. Lactones such as γ-butyrolactone, γ-valerolactone, and higher analogues generally did not support cell growth when used as the sole carbon source. Co-feeding of lactones with glucose enhanced the utilization of lactones for both copolyester accumulation and cell growth. The copolyester from the cells grown on the mixed substrates of glucose (10 g/L) and γ-valerolactone (1–3 mL/L) was poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (P(3HB-co-3HV)), while cells grown with γ-butyrolactone (1–3 mL/L) as a cosubstrate produced poly(3-hydroxybutyrate-co-4-hydroxybutyrate) (P(3HB-co-4HB)). The values of parameter D, calculated from the NMR dyad-sequence data for polymer samples obtained after 72 h of cultivation, showed lactone concentration dependences differing among lactones. The time-course data obtained from growth on the cosubstrates of γ-valerolactone (2 mL/L) and glucose (10 g/L) revealed that 3HV-rich copolymers were synthesized in the early growth phase, and the 3HB-rich fraction steadily increased in the later accumulation phase and then peaked at 80 h when γ-valerolactone was depleted. These polyhydroxyalkanoate accumulation profiles suggested a high D value of the final product, whose value was determined to be 3.25. γ-Valerolactone was consumed faster than γ-butyrolactone. The difference between the assimilation behavior of the two lactones was discussed in relation to the heterogeneity of the final copolyester products. A correlation between NMR microstructure and the physiology of polyhydroxyalkanoate accumulation was observed.Key words: microstructural heterogeneity, bacterial copolyesters, lactones, Hydrogenophaga pseudoflava.