Relationship of Intracellular Coenzyme F420 Content to Growth and Metabolic Activity of Methanobacterium bryantii and Methanosarcina barkeri

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The use of F420 as a parameter for growth or metabolic activity of methanogenic bacteria was investigated. Two representative species of methanogens were grown in batch culture: Methanobacterium bryantii (strain M.o.H.G.) on H2 and CO2, and Methanosarcina barkeri (strain Fusaro) on methanol or acetate. The total intracellular content of coenzyme F420 was followed by high-resolution fluorescence spectroscopy. F420 concentration in M. bryantii ranged from 1.84 to 3.65 μmol · g of protein−1; and in M. barkeri grown with methanol it ranged from 0.84 to 1.54 μmol · g−1 depending on growth conditions. The content of F420 in M. barkeri was influenced by a factor of 2 depending on the composition of the medium (minimal or complex) and by a factor of 3 to 4 depending on whether methanol or acetate was used as the carbon source. A comparison of F420 content with protein, cell dry weight, optical density, and specific methane production rate showed that the intracellular content of F420 approximately followed the increase in biomass in both strains. In contrast, no correlation was found between specific methane production rate and intracellular F420 content. However, qCH4(F420), calculated by dividing the methane production rate by the coenzyme F420 concentration, almost paralleled qCH4(protein). These results suggest that F420 may be used as a specific parameter for estimating the biomass, but not the metabolic activity, of methanogens; hence qCH4(F420) determined in mixed populations with complex carbon substrates must be considered as measure of the actual methanogenic activity and not as a measure of potential activity.

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