Extracellular polysaccharide production by methylobacterium organophilum NCIB 11278 from methanol

Abstract

Some methylotrophs were studied with their ability of poly-$\beta$-hydroxybutyrate production and extracellular polysaccharide production from methanol as a sole source of carbon. Methylobacterium organophilum NCIB 11278, a facultative methylotroph, originally isolated as a methane-utilizing bacterium, not only accumulates the poly- v$\beta$ -hydroxybutyrate, but also produces the extracellular polysaccharide on a minimum synthetic medium. For the efficient production of the polysaccharide from Methylobacterium organophilum NCIB 11278, the effect of the medium components and culture conditions were studied in batch culture. The optimal concentrations of medium components for maximum polysaccharide production were as follows; Methanol, 0.5\% (v/v); $(NH_4)_2SO_4$, 0.3 g /l; $Na_2HPO_4$, 1.06 g/l; $KH_2PO_4$, 0.65 g/l; $MgSO_4$, 0.45 g /l; and trace elements. The optimal pH and temperature for polysaccharide production were 6-7 and $30\,^\circ\!C$, respectively. This organism grew on 0.25\% (v/v) methanol with a maximum specific growth rate of 0.28 $hr^{-1}$. Methanol concentration higher than 4.0\% (v/v) was toxic. The maximum polysaccharide productivity (P/X) was obtained 0.42 g-polysaccharide/ g-DCW with 0.5\% methanol in batch culture. The substrate (methanol) inhibition and toxicity in polysaccharide production were recovered by constant fed-batch culture which was carried out by a fixed feeding rate (1.0 ml/min) with methanol containing media. The production of polysaccharide was stimulated by deficiency of nutrients except carbon source. By constant fed-batch culture, the polysaccharide was produced to 0.95 g together with 1.0 g of dry cells, per liter of the culture broth. The maximal productivity on methanol was enhanced to more than twice times by constant fed-batch culture as compared with the batch culture. And the optimal C/N molar ratio of feeding liquid is 100.