Methanosarcina

Methanosarcina is a genus of euryarchaeote archaea that produce methane. These single-celled organisms are known as anaerobic methanogens that produce methane using all three metabolic pathways for methanogenesis. They live in diverse environments where they can remain safe from the effects of oxygen, whether on the earth's surface, in groundwater, in deep sea vents, and in animal digestive tracts. Methanosarcina grow in colonies. The amino acid pyrrolysine was first discovered in a Methanosarcina species, M. barkeri. Primitive versions of hemoglobin have been found in M. acetivorans, suggesting the microbe or an ancestor of it may have played a crucial role in the evolution of life on Earth. Species of Methanosarcina are also noted for unusually large genomes. M. acetivorans has the largest known genome of any archaeon. According to a theory published in 2014, Methanosarcina may have been largely responsible for the largest extinction event in the Earth's history, the Permian–Triassic extinction event. The theory suggests that acquisition of a new metabolic pathway via gene transfer followed by exponential reproduction allowed the microbe to rapidly consume vast deposits of organic carbon in marine sediments, leading to a sharp buildup of methane and carbon dioxide in the Earth's oceans and atmosphere that killed around 90% of the world's species. This theory could better explain the observed carbon isotope level in period deposits than other theories such as volcanic activity. Methanosarcina has been used in waste water treatment since the mid-1980s. Researchers have sought ways to use it as an alternative power source. Methanosarcina strains were grown in single-cell morphology (Sowers et al. 1993) at 35 °C in HS broth medium containing 125 mM methanol plus 40 mM sodium acetate (HS-MA medium). Methanosarcina may be the only known anaerobic methanogens that produce methane using all three known metabolic pathways for methanogenesis. Methanogenesis is critical to the waste-treatment industry and biologically produced methane also represents an important alternative fuel source. Most methanogens make methane from carbon dioxide and hydrogen gas. Others utilize acetate in the acetoclastic pathway. In addition to these two pathways, species of Methanosarcina can also metabolize methylated one-carbon compounds through methylotrophic methanogenesis. Such one-carbon compounds include methylamines, methanol, and methyl thiols. Only Methanosarcina species possess all three known pathways for methanogenesis, and are capable of utilizing no less than nine methanogenic substrates, including acetate. Methanosarcina are the world's most diverse methanogens in terms of ecology. They are found in environments such as landfills, sewage heaps, deep sea vents, deep subsurface groundwater, and even in the gut of many different ungulates, including cows, sheep, goats, and deer. Methanosarcina have also been found in the human digestive tract. M. barkeri can withstand extreme temperature fluctuations and go without water for extended periods. It can consume a variety of compounds or survive solely on hydrogen and carbon dioxide. It can also survive in low pH environments that are typically hazardous for life. Noting its extreme versatility, biologist Kevin Sowers postulated that M. barkeri could even survive on Mars. Methanosarcina grow in colonies and show primitive cellular differentiation. In 2002, the amino acid pyrrolysine was discovered in M. barkeri by Ohio State University researchers. Earlier research by the team had shown that a gene in M. barkeri had an in-frame amber (UAG) codon that did not signal the end of a protein, as would normally be expected. This behavior suggested the possibility of an unknown amino acid which was confirmed over several years by slicing the protein into peptides and sequencing them. Pyrrolysine was the first genetically-encoded amino acid discovered since 1986, and 22nd overall. It has subsequently been found throughout the family Methanosarcinaceae as well as in a single bacterium, Desulfitobacterium hafniense. Both M. acetivorans and M. mazei have exceptionally large genomes. As of August 2008, M. acetivorans possessed the largest sequenced archaeal genome with 5,751,492 base pairs. The genome of M. mazei has 4,096,345 base pairs.