Methanosarcina acetivorans

Methanosarcina acetivorans is a versatile methane producing microbe which is found in such diverse environments as oil wells, trash dumps, deep sea hydrothermal vents, and oxygen depleted sediments beneath kelp beds. Only M. acetivorans and microbes in the genus Methanosarcina use all three known metabolic pathways for methanogenesis. Methanosarcinides, including M. acetivorans, are also the only archaea capable of forming multicellular colonies, and even show cellular differentiation. As of 2006, the genome of M. acetivorans is the largest of all sequenced archaeal genomes. 

In 2006, James G. Ferry and Christopher House discovered that M. acetivorans uses a previously unknown metabolic pathway to metabolize carbon monoxide into methane and acetate using the well known enzymes phosphotransacetylase (PTS) and acetate kinase (ACK). This pathway is surprisingly simple, and has been proposed by Ferry and House as perhaps the first metabolic pathway used by primordial microbes. Other theories of the primordial metabolic biochemistry include heterotrophic theory and chemoautotrophic theory, but both these theories have been criticised as being far too complex to have arisen spontaneously.

However, in the presence of minerals containing iron sulfides, as might have be found in sediments in a primordial environment, acetate would be catalytically converted into acetate thioester, a sulfur-containing derivative. Primitive microbes could obtain biochemical energy in the form of adenosine triphosphate (ATP) by converting acetate thioester back into acetate using PTS and ACK, which would then be converted back into acetate thioester to complete the process. In such an environment, a primitive "protocell" could easily produce energy through this metabolic pathway, excreting acetate as waste. Furthermore, ACK catalyzes the synthesis of ATP directly. Other pathways generate energy from ATP only through complex multi-enzyme reactions involving protein pumps and osmotic imbalances across a membrane.