| The biochemistry of the methylotrophs was analyzed and theoretical yields for biomass and energy reserve products were calculated for methane and methanol on a few variations on the energy transduction pathways. Catabolic pathway was the dominant route of carbon utilization. NADH was the most important variable in determination of the yield.; Growth of methylotrophs was experimentally investigated in fed batch, and continuous cultures, using methane and methanol. Choice of substrate had minor influence on the rates of growth or product synthesis. Under typical operating conditions, fed batch cultures accumulated approximately 50% of total dry weight as energy reserve materials. PHB accounted for 9% of the total dry weight during nitrogen limitation. When cultivated under oxygen limitation, PHB content reached 45% of the dry weight.; Chemostat cultures exhibited an inverse relationship between biomass and dilution rate. Under nitrogen limitation, 26% of the dry weight was the highest proportion of PHB obtained. Similar values were obtained for sulfur and oxygen limitation. Shift oxygen limitation resulted in a rise in the rate of PHB synthesis, evidence of an active electron transport system. By maintaining the dissolved oxygen concentration at zero, PHB and Lipid biosynthetic pathways could be harnessed as metabolic shunts for the excess NADH production.; Mixed substrate utilization was noted in fed batch fermentations for M. parvus but without concomitant biosynthesis. Uncoupling of energy metabolism, and biomass production was observed in fed-batch and continuous cultures during excess oxygen supply, indicating that the catabolic pathway operated in excess of the required level.; Models which describe the rates of nutrient utilization, and product formation were formulated. Starting with simple unstructured models, greater complexity was added to account for the assimilatory, dissimilatory pathways, and the metabolic shunts for overflow products. By incorporating energy production mechanisms, strict accounting for the fate of methane was possible. The model was used to forecast effects of various substrate concentrations on the metabolic flow of carbon. Good fit was observed with fed-batch and continuous culture data from methane fermentations. In methanol fermentations, the model was found useful in predicting responses to various nutrient feed modes. |
