Abstract
Although Methanosarcinales are versatile concerning their methanogenic substrates, the ability of Methanosarcina thermophila to use carbon dioxide (CO2) for catabolic and anabolic metabolism was not proven until now. Here, we show that M. thermophila used CO2 to perform hydrogenotrophic methanogenesis in the presence as well as in the absence of methanol. During incubation with hydrogen, the methanogen utilized the substrates methanol and CO2 consecutively, resulting in a biphasic methane production. Growth exclusively from CO2 occurred slowly but reproducibly with concomitant production of biomass, verified by DNA quantification. Besides verification through multiple transfers into fresh medium, the identity of the culture was confirmed by 16s RNA sequencing, and the incorporation of carbon atoms from 13CO2 into 13CH4 molecules was measured to validate the obtained data. New insights into the physiology of M. thermophila can serve as reference for genomic analyses to link genes with metabolic features in uncultured organisms.
Highlights
Biogenic methane (CH4) is produced by methanogenic archaea, using three main substrates: acetate, CO2, and substances containing a methyl group [1] (Table 1)
Hydrogen-independent methanogenesis involves the reduction of methyl groups with electrons deriving from the oxidation of further methyl groups, so that for each three CH4 molecules, one molecule of CO2 is produced [1, 5]
Methanosarcina thermophila was grown on a mineral medium containing methanol and H2/CO2 in the headspace (Figure 1)
Summary
Biogenic methane (CH4) is produced by methanogenic archaea, using three main substrates: acetate, CO2, and substances containing a methyl group [1] (Table 1). Only the order Methanosarcinales includes members able to metabolize all three substrates [1]. Acetoclastic methanogenesis is exclusively performed by the genera Methanosarcina and Methanosaeta, both members of the Methanosarcinales, which differ in their substrate specificity and their affinity to acetate [1, 2]. Methylotrophic methanogenesis can be hydrogen-dependent or hydrogen-independent and is limited to Methanosarcinales, Methanomassiliicoccales, and one species of Methanobacteriales [1, 3]. Hydrogen-dependent species use hydrogen (H2) to reduce the methyl group to CH4 [1, 5]. Hydrogen-independent methanogenesis involves the reduction of methyl groups with electrons deriving from the oxidation of further methyl groups, so that for each three CH4 molecules, one molecule of CO2 is produced [1, 5]
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