The effect of oxygen on methanol oxidation by an obligate methanotrophic bacterium studied by in vivo C-13 nuclear magnetic resonance spectroscopy

C-13 NMR was used to study the effect of oxygen on methanol oxidation by a type II methanotrophic bacterium isolated from a bioreactor in which methan e was used as electron donor for denitrification. Under high (35-25%) oxyge n conditions the first step of methanol oxidation to formaldehyde was much faster than the following conversions to formate and carbon dioxide. Due to this the accumulation of formaldehyde led to a poisoning of the cells. A m ore balanced conversion of C-13-labelled methanol to carbon dioxide was obs erved at low (1-5%) oxygen concentrations. In this case, formaldehyde was s lowly converted to formate and carbon dioxide. Formaldehyde did not accumul ate to inhibitory levels. The oxygen-dependent formation of formaldehyde an d formate from methanol is discussed kinetically and thermodynamically.