Relationship of Intracellular Coenzyme F 420 Content to Growth and Metabolic Activity of Methanobacterium bryantii and Methanosarcina barkeri

Abstract

The use of F 420 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 H 2 and CO 2 , and Methanosarcina barkeri (strain Fusaro) on methanol or acetate. The total intracellular content of coenzyme F 420 was followed by high-resolution fluorescence spectroscopy. F 420 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 F 420 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 F 420 content with protein, cell dry weight, optical density, and specific methane production rate showed that the intracellular content of F 420 approximately followed the increase in biomass in both strains. In contrast, no correlation was found between specific methane production rate and intracellular F 420 content. However, qCH 4 (F 420 ), calculated by dividing the methane production rate by the coenzyme F 420 concentration, almost paralleled qCH 4 (protein). These results suggest that F 420 may be used as a specific parameter for estimating the biomass, but not the metabolic activity, of methanogens; hence qCH 4 (F 420 ) 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.