2:45 PM - 3:00 PM
[BBG01-04] Non-methanogenic Archaea Within Canonical Methanogen Orders
Keywords:serpentinization, Methanogen, acetogen
Serpentinization, the reaction of olivine- and pyroxene-rich rocks with water, produces magnetite, hydroxide, and serpentine minerals. It also generates molecular hydrogen, which can be utilized by chemosynthetic organisms. Considering that this reaction may have occurred or currently occurs on early Mars or icy worlds, where highly reducing mineralogy was likely widespread, the microbial ecosystems associated with serpentinization on present-day Earth are considered important analogs for those ecosystems if they exist elsewhere.
The Cedars is a zone of active serpentinization located in Northern California. The deep groundwaters are highly alkaline (pH 11.5-12.0) and extremely low redox potential (Eh < −650 mV) and host microbial communities with low cell density (102 cells/mL).
The community composition comprises more than 60% are bacterial members of the episymbiotic group Patescibacteria with the remainder comprised of potential acetogens encoding reductive acetyl-CoA pathway. Although the spring waters of The Cedars are saturated with molecular hydrogen and an acetogen generally fixes CO2 coupled to oxidation of hydrogen, several metagenome-assembled genomes do not encode the hydrogenase and/or formate dehydrogenases, both of which are required for conventional acetogenesis. Here, we circularized the genome of Met12, an archaeon in the order Methanocellales (now reclassified as class UBA148) within the phylum Halobacteriota detected from serpentinized springs in The Cedars, California, and revealed it to be the first member of the canonical methanogenic orders that have an acetyl-CoA pathway but lack essential genes for methanogenesis including the methyl-coenzyme M reductase (Mcr), heterodisulfide reductases (Hdr) and hydrogenases (Suzuki et al., 2024). A comparative genomic analysis revealed that the absence of Mcr is a common feature of the members in the class UBA148, which have also largely lost Hdr and hydrogenases. In situ transcriptomic analyses identified high expression of a multi-heme c-type cytochrome and the heterologous expression demonstrated that this cytochrome is capable of accepting electrons but not donating. All these suggested that Met12 is a CO2-reducing electron-fueled acetogen without electron bifurcation and the source of electron could be a highly reduced minerals existing in serpentinized settings.
References:
Suzuki, S., Ishii, S., Chadwick, G.L. et al. A non-methanogenic archaeon within the order Methanocellales. Nat Commun 15, 4858 (2024)
The Cedars is a zone of active serpentinization located in Northern California. The deep groundwaters are highly alkaline (pH 11.5-12.0) and extremely low redox potential (Eh < −650 mV) and host microbial communities with low cell density (102 cells/mL).
The community composition comprises more than 60% are bacterial members of the episymbiotic group Patescibacteria with the remainder comprised of potential acetogens encoding reductive acetyl-CoA pathway. Although the spring waters of The Cedars are saturated with molecular hydrogen and an acetogen generally fixes CO2 coupled to oxidation of hydrogen, several metagenome-assembled genomes do not encode the hydrogenase and/or formate dehydrogenases, both of which are required for conventional acetogenesis. Here, we circularized the genome of Met12, an archaeon in the order Methanocellales (now reclassified as class UBA148) within the phylum Halobacteriota detected from serpentinized springs in The Cedars, California, and revealed it to be the first member of the canonical methanogenic orders that have an acetyl-CoA pathway but lack essential genes for methanogenesis including the methyl-coenzyme M reductase (Mcr), heterodisulfide reductases (Hdr) and hydrogenases (Suzuki et al., 2024). A comparative genomic analysis revealed that the absence of Mcr is a common feature of the members in the class UBA148, which have also largely lost Hdr and hydrogenases. In situ transcriptomic analyses identified high expression of a multi-heme c-type cytochrome and the heterologous expression demonstrated that this cytochrome is capable of accepting electrons but not donating. All these suggested that Met12 is a CO2-reducing electron-fueled acetogen without electron bifurcation and the source of electron could be a highly reduced minerals existing in serpentinized settings.
References:
Suzuki, S., Ishii, S., Chadwick, G.L. et al. A non-methanogenic archaeon within the order Methanocellales. Nat Commun 15, 4858 (2024)