The physical and physiological factors influencing the production of exopolysaccharide(methylan) and poly-3-hydroxy butyrate(PHB) by Methylobacterium organophilum were investigated. Methanol was intermittently fed by a DO-stat method during the culture.
The effect of temperature and pH on cell growth and the polysaccharide and PHB production were studied. The maximum specific growth rate was determinated to be pH7 and 34℃, But the maximum cell density was obtained at pH7, 38℃. The maximum PHB and polysaccharide concentration were reached 1.791 g/l, 3.535 g/l at pH7, 38℃ and pH7, 30℃ respectively with the medium containing 0.6 g/l ammonium sulfate as a nitrogen source. Maximum PHB content reached 50% of dry cell weight at 38℃ and interestingly, no exopolysaccharide was produced at all at this temperature.
In the case of the culture with $Mo^{2+}$, $Mg^{2+}$, $Mn^{2+}$ or $K^+$-deficient medium under ammonium limitation, PHB accumulation was stimulated, whereas polysaccharide production was strongly inhibited. Under the condition of $Mg^{2+}$ or $Mn^{2+}$ deficiency, cell growth was almost the same as the control without any deficiency. Under the condition of $K^+$ limitation, cell growth was significantly limited. However, the maximum PHB content reached 60% of dry cell weight. The control of ratio of methanol to ammonium, in the feeding solution, were carrued out for the polysaccharide and PHB production. The higher ratio of C/N resulted in the lower cell growth and the higher content of PHB in dry cell weight and the higher production of polysaccharide. The specific rates of PHB production and polysaccharide production could be increased by feeding the lower ratio of C/N compared to the results obtained with feeding only methanol.
