Molecular weight characterization of poly[(R)-3-hydroxybutyrate] synthesized by genetically engineered strains of Escherichia coli

This study investigated the relationship of growth conditions, host strains and molecular weights of poly[(R)-3-hydroxybutyrate] [P(3HB)] synthesized by genetically engineered Escherichia coli. Various PHA synthases belonging to types I-IV enzymes were expressed in E. coli JM109 under the same experimental conditions, and the molecular weights of the polymers were characterized by gel permeation chromatography. The results demonstrate that P(3HB) polymers have varied molecular weights and polydispersities dependent on the characteristics of the individual PHA synthase employed. P(3HB) with high number-average molecular weights (Mn) [(1.5-4.0) × 106] and narrow polydispersities (1.6-1.8) were synthesized by PHA synthases from Ralstonia eutropha (type I), Delftia acidovorans (type I) and Allochromatium vinosum (type III). Contrary to these, P(3HB) with relatively low Mn [(0.17-0.79) × 106] and broad polydispersities (2.2-9.0) were synthesized by PHA synthases from Aeromonas caviae (type I), Pseudomonas sp. 61-3 (type II) and Bacillus sp. INT005 (type IV). Furthermore, the molecular weights of P(3HB) synthesized under various culture conditions, in various hosts of E. coli and by mutants of PHA synthase were characterized. It was found that, in addition to culture pH [Kusaka et al. Appl Microbiol Biotechnol 1997;47:140], other variances such as culture temperature, host strain and use of mutants are effective in changing polymer molecular weight.