Microbial growth on C1 compounds. Synthesis of cell constituents by methane- and methanol-grown Pseudomonas methanica |
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| Authors: | Patricia A Johnson and J R Quayle |
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| Affiliation: | Medical Research Council Cell Metabolism Research Unit, Department of Biochemistry, University of Oxford |
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| Abstract: | 1. A study has been made of the incorporation of carbon from 14C]methane, 14C]methanol and 14C]bicarbonate by cultures of Pseudomonas methanica growing on methane, and 14C]methanol by cultures of the same organism growing on methanol. 2. The distribution of radioactivity within the non-volatile constituents of the ethanol-soluble fractions of the cells, after incubation with labelled compound for periods up to 3min., has been analysed by chromatography and radioautography. 3. Over 90% of the radioactivity fixed from 14C]methane or 14C]methanol at the earliest times of sampling appeared in phosphorylated compounds. Glucose phosphate and fructose phosphate together constituted the largest part of the radioactive phosphates (70–90%); phosphoglycerate was a relatively minor component (2–17%). Other compounds becoming labelled during the incubation included glycine, serine, glutamate, aspartate, malate, citrate and alanine. 4. The first stable products of 14C]bicarbonate fixation were malate and aspartate (containing between them over 90% of the total radioactivity fixed at the earliest times of sampling). 5. The percentage of the total radioactivity fixed that was contained in each of the radioactive compounds has been plotted against time. The slopes of the curves obtained show that hexose phosphates are primary stable products of 14C]methane and 14C]methanol incorporation and that aspartate and malate are primary stable products of 14C]bicarbonate incorporation. 6. No carboxydismutase activity has been found in cell-free extracts of the organism. This fact, together with the other findings, shows that an autotrophic metabolism involving the ribulose diphosphate cycle of carbon dioxide fixation cannot be operating. |
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