Enhancement of polysaccharide-biopolymer productivity from methanol by methylobacterium organophilum

Abstract

In order to enhance the polysaccharide production from methanol by Methylobacterium organophilum, effects of addition of sugars and TCA-intermediates, and control of nitrogen fixation-favored conditions were investigated. The supplement of 4 g/l glucose and 0.01 M succinate to the fermentation medium increased the polysaccharide production by 2 times as compared with that obtained in only methanol containing medium as a organic substance. The other sugars showed no effects on cell growth and polysaccharide production, whereas malate had a slightly positive effects. By the intermittently feeding fed-batch culture using a DO-stat, effects of the dissolved oxygen level and the concentration of Mo$^{2+}$ and/or Fe$^{2+}$ were studied because these conditions might alter the nitrogen fixation activity of the cells. Cell growth was greatly repressed by oxygen-limitation but production yield(P/X) was not changed. When 6.4 mg/l sodium molybdate was added to the medium, cell growth and product yield were increased respectively 2.4 and 6.7 fold when compared with no Mo$^{2+}$ -containing control. The addition of FeSO4 increased both cell growth and Y$_{P/X}$ consistently with increasing concentration up to 10.8 mg/l. However, addition of FeSO4 into a medium containing excess sodium molybdate, resulted in reduced Y$_{P/X}$. Finally, by the addition of 6.4 mg/l Mo$^{2+}$ and 10.4 mg/l Fe$^{2+}$, 15 g/l cell mass and 8.5 g/l polysaccharide were obtained.