Effect of nutrient deficiency on accumulation and relative molecular weight of poly-?-hydroxybutyric acid by methylotrophic bacterium, Pseudomonas 135

Abstract

Pseudomonas 135, a facultative methylotroph, was cultivated on methanol as a sole carbon and energy source for the accumulation of poly-β-hydroxybutyric acid (PHB). The cells grew fairly well on minimal synthetic medium containing 0.5% (v/v) of methanol at pH 7.0 and 30° C. The maximum specific growth rate was determined to be 0.26–0.28 h−1 with a growth yield of 0.38 in the optimized growth medium. For stimulation of PHB accumulation in the cells, deficiency of nutrients such as NHinf4sup+, Mg2+ and POinf4sup3−was crucial even though cell growth was significantly suppressed. The PHB content of a 40-h culture was determined to be 37% of the total cell mass in NHinf4sup+-limited medium, 42.5% on Mg2+-deficient medium, and 34.5% on POinf4sup3−-deficient medium. The maximum content of PHB in the cells could reach 55% in NHinf4sup+-limited fed-batch culture. The average relative molecular eight determined by gel permeation chromatography was 3.7 × 105 in NHinf4sup+-limited culture, 2.5 × 105 in Mg2+-deficientmedium, and 3.1 × 105 in POinf4sup3−-deficient medium. Polydispersity determined in each culture was relatively high (about 10–11). The solid PHB had a melting temperature of 173° C.