Microbial growth on C1 compounds. Uptake of [14C]formaldehyde and [14C]formate by methane-grown Pseudomonas methanica and determination of the hexose labelling pattern after brief incubation with [14C]methanol.

1. A study has been made of the incorporation of carbon from [(14)C]formaldehyde and [(14)C]formate by cultures of Pseudomonas methanica growing on methane. 2. The distribution of radioactivity within the non-volatile constituents of the ethanol-soluble fractions of the cells, after incubation with labelled compounds for periods of up to 1min., has been analysed by chromatography and radioautography. 3. Radioactivity was fixed from [(14)C]formaldehyde mainly into the phosphates of the sugars, glucose, fructose, sedoheptulose and allulose. 4. Very little radioactivity was fixed from [(14)C]formate; after 1min. the only products identified were serine and malate. 5. The distribution of radioactivity within the carbon skeleton of glucose, obtained from short-term incubations with [(14)C]methanol of Pseudomonas methanica growing on methane, has been investigated. At the earliest time of sampling over 70% of the radioactivity was located in C-1; as the time increased the radioactivity spread throughout the molecule. 6. The results have been interpreted in terms of a variant of the pentose phosphate cycle, involving the condensation of formaldehyde with C-1 of ribose 5-phosphate to give allulose phosphate.