Summary: produced viscous and non-viscous exopolysaccharides (EPS) when grown in batch culture. Both types contained glucose, galactose, mannose and an unidentified 6-desoxyhexose, and were substituted with pyruvate and acetate residues. When the organism was grown in continuous culture only the non-viscous EPS was synthesized; the rate of production was 18·5 mg h (g biomass) in methanol-limited cultures and increased by approximately 3- and 4-fold when growth was limited by oxygen or nitrogen respectively. The specific activity of methanol dehydrogenase in cell extracts was relatively low when bacteria were grown under conditions of methanol excess and increased 2-fold in carbon-limited cells, reflecting the need to ‘scavenge’ the small amounts of available methanol. In contrast, the specific activities of several key enzymes of the ribulose monophosphate (RuMP) pathway were greater in cells grown under conditions of nitrogen or oxygen limitation than when growth was Limited by the availability of carbon, indicating the potential for increased carbon flux round the cycle when excess methanol was present in the growth medium. When methylotrophs are grown under conditions of methanol excess it is important that there is a mechanism to prevent the overproduction of formaldehyde, and we suggest that these changes in EPS production and in the specific activities of the key enzymes of the RuMP cycle are necessary for the efficient removal of this toxic metabolite of methanol.


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