Environmental regulation of alcohol metabolism in thermotolerant methylotrophic Bacillus strains |
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Authors: | N Arfman K J de Vries H R Moezelaar M M Attwood G K Robinson M van Geel L Dijkhuizen |
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Institution: | (1) Department of Microbiology, University of Groningen, NL-9751 NN Haren, The Netherlands;(2) Department of Microbiology, University of Sheffield, S10 2TN Sheffield, UK |
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Abstract: | The thermotolerant methylotroph Bacillus sp. C1 possesses a novel NAD-dependent methanol dehydrogenase (MDH), with distinct structural and mechanistic properties. During growth on methanol and ethanol, MDH was responsible for the oxidation of both these substrates. MDH activity in cells grown on methanol or glucose was inversely related to the growth rate. Highest activity levels were observed in cells grown on the C1-substrates methanol and formaldehyde. The affinity of MDH for alcohol substrates and NAD, as well as V
max, are strongly increased in the presence of a M
r 50,000 activator protein plus Mg2+-ions Arfman et al. (1991) J Biol Chem 266: 3955–3960]. Under all growth conditions tested the cells contained an approximately 18-fold molar excess of (decameric) MDH over (dimeric) activator protein. Expression of hexulose-6-phosphate synthase (HPS), the key enzyme of the RuMP cycle, was probably induced by the substrate formaldehyde. Cells with high MDH and low HPS activity levels immediately accumulated (toxic) formaldehyde when exposed to a transient increase in methanol concentration. Similarly, cells with high MDH and low CoA-linked NAD-dependent acetaldehyde dehydrogenase activity levels produced acetaldehyde when subjected to a rise in ethanol concentration. Problems frequently observed in establishing cultures of methylotrophic bacilli on methanol- or ethanol-containing media are (in part) assigned to these phenomena.Abbreviations MDH
NAD-dependent methanol dehydrogenase
- ADH
NAD-dependent alcohol dehydrogenase
- A1DH
CoA-linked NAD-dependent aldehyde dehydrogenase
- HPS
hexulose-6-phosphate synthase
- G6Pdh
glucose-6-phosphate dehydrogenase |
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Keywords: | Bacillus Thermotolerance Methylotrophy Methanol dehydrogenase Activator protein RuMP cycle of formaldehyde fixation Hexulose-6-phosphate synthase Continuous culture Methanol limitation |
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