[Lithotrophic metabolic elements in the obligate methylotroph, Methylococcus thermophilus]

Methane oxidizing bacteria oxidize ammonium via hydroxylamine to nitrite. Electrons liberated upon oxidation of hydroxylamine are transported, depending on the conditions, by the components of the respiratory chain either to oxygen or to pyridine nucleotide. In the former case, the process is coupled with ATP synthesis which occurs at the level of terminal oxidase; in the latter case, NAD+ is reduced by the energy-dependent reversed electron flow in the respiratory chain. The level of nitrite accumulation in the culture liquid of methane oxidizing bacteria suggests that the process of ammonium nitrification is a necessary step of their metabolism. Therefore, oxidation of the mineral component of the growth medium (i. e. ammonium) is an additional source of metabolic energy for the obligate methane oxidizing bacterium Methylococcus thermophilus. Operation of the lithotrophic type of mechanism for energy production at the account of ammonium oxidation makes methane oxidizing bacteria similar to nitrifying microorganisms.