Optimization of culture conditions for production of a high viscosity polysaccharide, methylan, by methylobacterium organophilum from methanol

Abstract

An extracellular polysaccharide, methylan, was produced under the specific conditions by Methylobacteriurn organophilum from methanol. The specific growth rate of cells was approximately constant regardless of C/N ratio and the specific product yield was maximum at a C/N ratio of 30. Methylan production was suppressed by the deficiency of mineral ions such as Mn** or Fe** ion. The optimal pH for cell growth and methylan production was 7. Whereas the optimal temperature for cell growth was found to be 37°C, that for methylan production was 30°C. The methanol concentration above 4% completely inhibited the cell growth. The initial methanol concentration for the maximal production of methylan was 0.5% (v/v) and above this concentration, methylan production was markedly inhibited. To overcome the substrate toxicity and inhibition for both cell growth and methylan production, a fed-bach culture of intermittent feeding within 5 g/l methanol was conducted under the optimal culture condition. Methylan production of was stimulated by nitrogen limitation and methylan was accumulated up to 8.7 g/l and cell mass also increased up to 12.4 g/l.