Distribution of methanol carbon between assimilation and oxidation pathways in methanol-grown Pseudomonas C

In Pseudomonas C, a facultative methylotrophic bacterium, methanol is assimilated via the 2-keto-3-deoxy-6-phosphogluconate (KDPG) variant of the ribulose monophosphate (RMP) pathway of formaldehyde fixation. The oxidation of methanol to CO2 is accomplished by the direct oxidation pathway (which involves formic acid as an oxidation intermediate), via a cyclic oxidation pathway (glucose monophosphate shunt) and by other decarboxylation reactions. The distribution pattern of methanol carbon among the assimilation and the different oxidation pathways was studied by measuring the distribution between CO2 and cell constituents of 14C-labelled compounds after their injection into a culture growing on methanol in a chemostat. From these measurements, it was calculated that 25% of the methanol consumed by the cells was oxidized through formate to CO2, while the remainder was diverted into the hexulosephosphate synthase reaction from which 55% was assimilated through the KDPG reaction and 17% was oxidized to CO2 via a cyclic oxidation pathway and other decarboxylation reactions. The remaining 7% from the methanol carbon was re-incorporated as CO2 into cell material through carboxylation reactions.