Fig. 6. A model of the biogeochemical roles of Brockarchaeota in the anaerobic carbon cycle.

C1 and methylated compounds, such as methanol or methylamines, are utilized biologically as carbon and energy sources in the ocean and deep-sea sediments resulting in a considerable carbon reservoir. The biodegradation of organic carbon in the water column and subsurface is a source of these compounds. The utilization of methyl compounds as precursors in methane synthesis is confined to a small group of methylotrophic methanogens (i.e., Verstraetearchaeota). The only described anaerobic methylotrophs include members of methanogenic archaea, acetogenic bacteria, and sulfate-reducing bacteria. These organisms compete for these compounds geochemically produced in anoxic settings. Brockarchaeota may recycle methanol and methylamines in anoxic environments without methane formation and may be sequestered in deep sea sediments and hot springs. Orange and purple arrows represent sources and sinks, respectively. Organic Matter (OM) includes dissolved and particulate organic matter feeding the microbial loop (adapted from Evans et al., 2019 and Zhuang et al., 2018).