SUMMARY: The regulation of the enzymes associated with one-carbon metabolism and the assimilation of nitrogen, together with the cellular composition of X, were investigated. The effect of changing the methanol-carbon concentration with the NH -nitrogen concentration remaining constant (C: N ratio) in the medium during chemostat growth at a constant dilution rate was studied. As the medium changed from a C-limitation to a dual C- and N- and finally a N-limitation, the culture gradually passed through three definite growth phases. In response to these environmental conditions the cellular composition and the specific enzyme activity patterns changed. The C-content of the cells changed very little. The N- and protein-content was constant over C-limiting conditions, but under dual C- and N-limiting and N-limiting conditions an accumulation of poly-β-hydroxybutyrate (PHB) occurred and as a consequence the N-content and protein-content of the cells decreased. The enzyme associated with N-assimilation during C-limitation was an NADP-dependent glutamate dehydrogenase which was replaced by the high affinity glutamine synthetase and glutamate synthase pathway immediately the NH4 concentration in the medium became limiting. Similarly the specific activity of methanol dehydrogenase, which was high during C-limiting conditions, dropped to a low level as the NH -N concentration decreased. Finally carbon balances were constructed throughout the experiment which showed that irrespective of the C:N ratio in the medium during C-limitation, the methanol-carbon was fluxed into biomass and CO only; during dual limitation the carbon was channelled into biomass, CO and PHB; and finally when the growth was in the presence of excess carbon no methanol-carbon was directed into over-metabolite production but, instead, the excess carbon was oxidized through the dissimilatory pathway.


Article metrics loading...

Loading full text...

Full text loading...


Most cited this month Most Cited RSS feed

This is a required field
Please enter a valid email address
Approval was a Success
Invalid data
An Error Occurred
Approval was partially successful, following selected items could not be processed due to error