EFFECT OF NUTRIENT DEFICIENCY ON ACCUMULATION AND RELATIVE MOLECULAR-WEIGHT OF POLY-BETA-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-beta-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-degrees-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 NH4+, Mg2+ and PO43- 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 NH4+-limited medium, 42.5% on Mg2+-deficient medium, and 34.5% on PO43- -deficient medium. The maximum content of PHB in the cells could reach 55% in NH4+-limited fed-batch culture. The average relative molecular eight determined by gel permeation chromatography was 3.7 x 1O(5) in NH4+-limited culture, 2.5 x 10(5) in Mg2+-deficient mediUm, and 3.1 x 10(5) in PO43--deficient medium. Polydispersity determined in each culture was relatively high (about 10-(11)). The solid PHB had a melting temperatue of 173-degrees-C.