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Zusammenfassung:
Genome Scale Metabolic Models (GSMMs) of the recently sequenced
Methylocystis hirsuta and two other methanotrophs from the genus
Methylocystis have been reconstructed. These organisms are Type II
methanotrophs with the ability of accumulating Polyhydroxyalkanoates
under nutrient limiting conditions. For the first time, GSMMs have been
reconstructed for Type II methanotrophs. These models, combined with
experimental biomass and PHB yields of Methylocystis hirsuta, allowed
elucidating the methane oxidation mechanism by the enzyme pMMO
(particulate methane monooxygenase) in these organisms. In contrast to
Type I methanotrophs, which use the "direct coupling mechanism", Type II
methanotrophs appear to use the so called "redox arm mechanism". The
utilization of the "redox arm mechanism", which involves the coupling
between methane oxidation and complex I of the respiratory chain, was
confirmed by inhibition of complex I with catechol. Utilization of the
"redox arm" mechanism leads to lower biomass yields on methane compared
to Type I methanotrophs. However, the ability of Type II methanotrophs
to redirect high metabolic carbon fluxes towards acetoacetyl-CoA under
nitrogen limiting conditions makes these organisms promising platforms
for metabolic engineering.
