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Regulation of methanol oxidation and carbon dioxide fixation in Xanthobacter strain 25a grown in continuous culture Croes, L.M.; Meijer, Wilhelmus; Dijkhuizen, L. Take-down policy If you believe that this document breaches copyright please contact us providing details, and we will remove access to the work immediately and investigate your claim. Abstract. The regulation of Cl-metabolism in Xanthobacter strain 25 a was studied during growth of the organism on acetate, formate and methanol in chemostat cultures. No activity of methanol dehydrogenase (MDH), formate dehydrogenase (FDS) or ribulose-l,5-bisphosphate carboxylase/oxygenase (RuBisC/O) could be detected in cells grown on acetate alone over a range of dilution rates tested. Addition of methanol or formate to the feed resulted in the immediate induction of MDH and FDH and complete utilization (D = 0.10 h-1) of acetate and the Cl-substrates. The activities of these enzymes rapidly dropped at the higher growth rates, which suggests that their synthesis is further controlled via repression by "heterotrophic" substrates such as acetate. Synthesis of RuBisC/O already occurred at low methanol concentrations in the feed, resulting in additive growth yields on acetate/methanol mixtures. The energy generated in the oxidation of formate initially allowed an increased assimilation of acetate (and a decreased dissimilation), resulting in enhanced growth yields on the mixture. RuBisC/O activity could only be detected at the higher formate/acetate ratios in the feed. The data suggest that synthesis of RuBisC/O and CO2 fixation via the Calvin cycle in Xanthobacter strain 25 a is controlled via a (de)repression mechanism, as is the case in other facultatively autotrophic bacteria. Autotrophic CO2 fixation only occurs under conditions with a diminished supply of "heterotrophic" carbon sources and a sufficiently high availability of suitable energy sources. The latter point is further supported by the clearly more pronounced derepressing effect exerted by methanol compared to formate. Offprint requests to: L. DijkhuizenAbbreviations: FDH, formate dehydrogenase; FBPase, fructose-1,6-bisphosphatase; ICDH, isocitrate dehydrogenase; MDH, methanol dehydrogenase; PQQ, pyrrolo quinoline quinone; PRK, phosphoribulokinase; RuBisC/O, ribulose-l,5-bisphosphate carboxylase/oxygenase; RUMP, ribulose monophosphate; TCA, tricarboxylic acid cycle

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Regulation of methylamine and formaldehyde metabolism in Arthrobacter P1. Effect of pulsewise addition of "heterotrophic" substrates to C1 substrate-limited continuous cultures Croes, L.M.; Tiesma, L.; Dijkhuizen, L.Citation for published version (APA): Croes, L. M., Tiesma, L., & Dijkhuizen, L. (1986). Regulation of methylamine and formaldehyde metabolism in Arthrobacter P1. Effect of pulse-wise addition of "heterotrophic" substrates to C1 substrate-limited continuous cultures. Archives of Microbiology, 144(3), 272-278. https://doi.Abstract. 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.