Taxonomy: Archaea; Euryarchaeota; Methanomicrobia; unclassified Methanomicrobia; Methanomassiliicoccus
Methanomassiliicoccus luminyensis is a recently cultivated Archaea species found in the human gut. This microbe produces methane by reducing methanol and oxidizing hydrogen and is one of the microbes in the human system that helps prevent the over abundance of hydrogen to maintain proper pH (Gorlas et al. 4745). M. luminyensis grows as single cell cocci measuring between 0.7 and 1 nanometers and grows optimally at 37°C, 7.6 pH, and 10 g/L NaCl concentration. When being cultivated in the lab, M. luminyensis requires tungsten to grow (Dridi 826–827).
A strain of Archaea, B10T, was isolated from human feces and was identified as M. luminyensis through 16S rRNA and mcrA gene sequences. Further characterization shows that B10T is non-motile and stains Gram-negative. M. luminyensis also exhibits auto fluorescence at 420nm, and a genome size of 2.05 Mb. The cell wall has been identified as having two layers, one thick and translucent, and the other thin and impermeable to electron beams. One distinguishing characteristic of B10T is the production of methane through the reduction of methanol, as an H2 obligate (B. Dridi et al. 1902–1905). M. luminyensis is unique from other Archaea found in humans as it has the largest genome and shows evidence of nonarchaeal proteins. It is speculated that these proteins originated from gene transfer with bacteria also found in the human gut (Gorlas et al. 4745). M. luminyensis has circular DNA with a 59.93% G+C DNA content (Dridi 826).
According to new research, there is no evidence of M. luminyensis or other methanogenics in children under 27 months, but a 60% presence in five year olds. This means these Archaea are likely to have arose from the environment. Genetics do not seem to play a role in the number of Archaea found in the gut (Dridi, Raoult, and Drancourt 63). Further evidence of M. luminyensis isolated in rice and groundwater suggest that the origin may be environmental. Methanobrevibacter smithii, Methanosphaera stadtmanae, and M. luminyensis are methanogenic Archaea found in human stool samples. M. luminyensis was present in 95% of patients with an average age of 62, with increased age as a predictor for only M. luminyensis. This positive correlation between increasing age and the presence of M. luminyensis was observed through statistical probability that showed 0.05 for patients under the age of 20 and an increase to 0.35 for those above the age of 60 (Bédis Dridi, Henry, et al. 774–776). This research indicates an increasing prevalence of M. luminyensis in older populations, with age but not gender as a determining factor of its presence.
When exposed to antibiotics, M. luminyensis demonstrated the same high resistance pattern that of Mb. Smithii. Remarkably, the archaeons susceptibility and resistance to antibiotics was related to the patterns seen in bacteria and eukarya. M. luminyensis was sensitive to antibiotics that both bacteria and eukarya were also susceptible to. However, M. luminyensis was resistant to antibiotics effective against only bacteria or only eukarya. This data allows researchers to begin to understand and formulate antimicrobial methods to further prevent infection (Bédis Dridi, Fardeau, et al. 2041–2043).
An interesting argument for a seventh order of methanogens has arisen in recent literature. An existing six orders of phylogenetically related methanogens has been previously established. "Candidatus Methanomethylophilus alvus" and M. luminyensis are a proposed seventh order of methanogens, differentiated from the previous six orders based on being obligate H2-dependent methylotrophic methanogens. M. luminyensis and "Ca. M. alvus" show an 87% similarity in their 16S rRNA gene sequences and their monophyletic lineage does not have a phylogenetic relationship with the existing six orders of methanogens. An analysis of the five markers for methanogenesis, in which all methanogens share, show evidence for vertical inheritance of genes (Borrel et al. 1771–1773). However, M. luminyensis and "Ca. M. alvus" do not have the genes for the first six steps of methanogenesis from H2/CO2, even though all other genomes of methanogens possess these genes (Borrel et al. 1778–1779). This further supports the argument that M. luminyensis and "Ca. M. alvus" constitute a seventh order of methanogens.
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