Abstract
Methylosinus trichosporium OB3b is an obligate aerobic methane-utilizing alpha-proteobacterium. Since its isolation, M. trichosporium OB3b has been established as a model organism to study methane metabolism in type II methanotrophs. M. trichosporium OB3b utilizes soluble and particulate methane monooxygenase (sMMO and pMMO respectively) for methane oxidation. While the source of electrons is known for sMMO, there is less consensus regarding electron donor to pMMO. To investigate this and other questions regarding methane metabolism, the genome-scale metabolic model for M. trichosporium OB3b (model ID: iMsOB3b) was reconstructed. The model accurately predicted oxygen: methane molar uptake ratios and specific growth rates on nitrate-supplemented medium with methane as carbon and energy source. The redox-arm mechanism which links methane oxidation with complex I of electron transport chain has been found to be the most optimal mode of electron transfer. The model was also qualitatively validated on ammonium-supplemented medium indicating its potential to accurately predict methane metabolism in different environmental conditions. Finally, in silico investigations regarding flux distribution in central carbon metabolism of M. trichosporium OB3b were performed. Overall, iMsOB3b can be used as an organism-specific knowledgebase and a platform for hypothesis-driven theoretical investigations of methane metabolism.
Highlights
The Gram-negative Methylosinus trichosporium OB3b belongs to an obligate aerobic methane oxidizing alpha-proteobacterium [1]. After it was isolated by Roger Whittenbury in 1970, M. trichosporium OB3b has been established as a model organism used to study methanotrophic metabolism [2]
The activation of particulate methane monooxygenase (pMMO) and soluble methane monooxygenase (sMMO) depends on the extracellular copper concentration. sMMO is expressed in medium with either low or no copper concentrations, whilst pMMO is expressed in mediums with relatively high copper concentrations [14,15]
We have found that redox-arm seems to be the most optimal mode of methane oxidation which agrees with previous findings
Summary
The Gram-negative Methylosinus trichosporium OB3b belongs to an obligate aerobic methane oxidizing alpha-proteobacterium (type II methanotrophs) [1]. SMMO is expressed in medium with either low or no copper concentrations, whilst pMMO is expressed in mediums with relatively high copper concentrations [14,15]. Both these enzymes need an electron donor to convert methane to methanol. Redox-arm mode: In this mode, ubiquinol is the electron donor for methane oxidation while methanol dehydrogenase (MDH) gives electrons via cytochrome c directly to complex IV. This leads up to proton motive force and ATP production. This mode of electron transfer has been suggested to be the main mode in Methylocystis, another type II methanotroph genus [17,18]
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