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

Summary

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 NH ^sup+_inf4 , Mg²⁺ and PO ^sup3−_inf4 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 NH ^sup+_inf4 -limited medium, 42.5% on Mg²⁺-deficient medium, and 34.5% on PO ^sup3−_inf4 -deficient medium. The maximum content of PHB in the cells could reach 55% in NH ^sup+_inf4 -limited fed-batch culture. The average relative molecular eight determined by gel permeation chromatography was 3.7 × 10⁵ in NH ^sup+_inf4 -limited culture, 2.5 × 10⁵ in Mg²⁺-deficientmedium, and 3.1 × 10⁵ in PO ^sup3−_inf4 -deficient medium. Polydispersity determined in each culture was relatively high (about 10–11). The solid PHB had a melting temperature of 173° C.