Regulation of methylamine and formaldehyde metabolism in Arthrobacter P1

The regulation of methylamine and formaldehyde metabolism in Arthrobacter P1 was investigated in carbonlimited continuous cultures. To avoid toxic effects of higher formaldehyde concentrations, formaldehyde-limited cultures were established in smooth substrate transitions from choline-limitation. Evidence was obtained that the synthesis of enzymes involved in the conversion of methylamine into formaldehyde and in formaldehyde fixation is induced sequentially in this organism. Compared to growth with methylamine the molar growth yield on formaldehyde was approximately 30% higher. This difference is mainly due to the expenditure of energy for the uptake of methylamine from the medium.The addition of a pulse of a heterotrophic substrate, glucose or acetate, to C₁ substrate-limited continuous cultures resulted in relief of carbon limitation and transient synthesis of increasing amounts of cell material. Concomitantly, a significant decrease in the specific activities of hexulose phosphate synthase was observed. However, the total activity of hexulose phosphate synthase in these cultures remained clearly in excess of that required to fix the formaldehyde that became available in time. The observed strong decrease in the specific activities of this RuMP cycle enzyme strongly suggests that its synthesis is controlled via catabolite repression exerted by the metabolism of heterotrophic substrates.Abbreviations HPS 3-Hexulose-6-phosphate synthase - HPI 3-hexulose-6-phosphate isomerase - RuMP ribulose monophosphate