Genus-specific remodeling of carbon and energy metabolism facilitates acetoclastic methanogenesis in <i>Methanosarcina</i> spp. and <i>Methanothrix</i> spp.

A large fraction of biogenic methane is derived from acetate, yet acetoclastic methanogens, i.e., methanogens that grow on acetate, remain poorly characterized due to their slow growth. Two groups of methanogens, <i>Methanosarcina</i> spp. and <i>Methanothrix</i> spp., perform acetoclastic methanogenesis using distinct sets of genes for acetate activation and energy conservation. It is widely hypothesized that these genetic modules from <i>Methanosarcina</i> spp. and <i>Methanothrix</i> spp. are functionally analogous and would thus be interchangeable. To test this hypothesis, we engineered different combinations of modules for acetoclastic growth in <i>Methanosarcina acetivorans</i>. Our results challenge this hypothesized paradigm of modularity, and we posit that other changes to the carbon and electron transfer pathways are crucial for the emergence of acetoclastic methanogenesis.