✍ Scribed by Yoshifumi Amano; Nobuo Takada; Hidekazu Sawada; Hideo Sakuma; Gyozo Terui
No coin nor oath required. For personal study only.
The cultural properties of an obligate methanol utilizer, Methylomonas methanolovorans, were investigated in batch and continuous cultures, and the problems of mass-energy balances were examined. Among the culture data, an exponential increase of growth lag with increased methanol concentration, as well as the inhibition kinetics in the relation between attainable maximum specific growth rate (p,,, 5 0.52) and methanol concentration are of interest. In the latter case, the inhibition constant ( K ; ) and the index number were 40 g/L, and 3 (dimensionless), respectively. The maximum yield coefficient (Y) in both batch and chemostat cultures was around 0.52. An analysis of the behavior of respiratory activity (Po,) in response to the dissolved oxygen concentration (DO) indicated that the oxygen-terminal entity should be regarded as a single one with a saturation constant for DO of 32 pg/L (1.1 X 10-6M). Chemostat data showed that the saturation constant for methanol is as low as 2.2 mg/L or 7 X 10-5M. A linear relationship was observed between the respiratory activity (mol O2 g-' h-') and the specific growth rate (p in h-'), with the relationship Q,, = 0.0504p + 0.00112. The theory of mass and energy balances used by Roels has been reformed to give useful relationships between RQ or the cell yield and p. In the case of M. rnethanolovorans, the relations can be greatly simplified since the influence of metabolic by-product formation was negligible. Experimental RQ values (theoretical values for Y = 0.52 and 0.445) at varying p-values were compared with theoretical ones; despite considerable fluctuations, the results were regarded to conform with theory. By use of massbalance equations and enthalpy data of known compounds, the heat evolution in methanol fermentation was estimated indirectly to be 612 kca1/100 g biomass formed. The YATp problems are also discussed.
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