Production of polysaccharide from methanol and properties of polysaccharide solution

Abstract

The production of polysaccharide by Methylobacterium organophilum, a facultative methylotroph, was carried out in batch and fed-batch culture system. At batch culture, the effect of $Mg^++$ and trace elements was investigated. Among them, the deficiency of $Fe^++$ and $Mn^++$ significantly repressed the cell growth and polysaccharide production. The optimal concentration of $MnSO_4$ and $FeSO_4$ were 0.13 -2mg/1, 1.3 -5.2 mg/1, respectively. However $Mg$^++$ and other metal ions didn``t affect the cell growth and polysaccharide production. As the nitrogen limitation accelerated the polysaccharide production, screening of adequate nitrogen sources was done. Cell growth was favored with inorganic nitrogen sources, but the polysaccharide production was favored with organic nitrogen sources. Unusually, the toxic effect of $(NH_4)_2SO_4$ on the cell growth was observed at concentration above 3 g/1 and specific growth rate decreased to half value of maximum specific growth rate., addition of $(NH_4)_2SO_4$ once after ammonium depletion, inhibitted the polysaccharide production and didn``t bring the cells to grow again. To overcome these phenomena, ammonium sulphate was added before ammonium depletion. By this technique, cell growth could be maintained actively and polysaccharide production was obtained as 2.4 g/1 with 1.3 g/1 of total $(NH_4)_2SO_4$. At fed-batch culture, three kinds of feeding modes; constant, intermittant and exponential were used to improve the polysaccharide production. By exponentially feeding fed-batch culture, accumulation of methanol was prevented and the production of polysaccharide was also to constant feeding fed-batch culture. The properties and rheological characteristics of polysaccharide solution were studied. Polysaccharide solution showed the characteristics of pseudoplastic, and thioxotropic fluid. The apparent viscosity of polysaccharide (10 g/1) was about 18000 cP which was almost 10 times higher than that of Xantan gum solution. ...