Growth yields of microorganisms on methanol and methane. A theoretical study

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Abstract
An attempt was made to calculate growth yields of microorganisms on methanol and methane on the basis of known biochemical pathways of C1 metabolism. Since 3‐phosphoglycerate is a key intermediate in the assimilation pathways of C1 compounds, the calculations were based on the assumption that the synthesis of cell material from C1 substrates can be regarded as a two step process. When YATP on 3‐phosphoglycerate was taken as 10.5, a maximal cell yield of organisms of the composition C4H8O2N on methanol was found to be 0.73 g cells/g substrate. For growth on methane a value of 0.91 g cells/g substrate was calculated when a mixed function oxidase was implicated in methane oxidation. These yields were calculated on the basis of the ribulose phosphate pathway of formaldehyde fixation as the major pathway of C1 assimilation. Yields calculated on the basis of the serine pathway were on an average 20% lower. The calculations disclosed that for growth on methane, at least for Methylococcus capsulatus, a reversed electron transport system is required when methane is oxidized by a mixed function oxidase. The theoretical cell yields on methanol and methane have been compared with experimentally obtained yields and the validity of the estimations of growth yields on the basis of the present calculations is discussed.

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