Bacterial aerobic methane cycling by the marine sponge-associated microbiome

Background Methanotrophy by the sponge-hosted microbiome has been mainly reported in the ecological context of deep-sea hydrocarbon seep niches where methane is either produced geothermically or via anaerobic methanogenic archaea inhabiting the sulfate-depleted sediments. However, methane oxidizing bacteria from the candidate phylum Binatota have recently been described and shown to be present in oxic shallow-water marine sponges, where sources of methane remain undescribed. Results Here, using an integrative - omics approach, we provide evidence for sponge-hosted bacterial methanogenesis occurring in fully oxygenated shallow water habitats. Specifically, we suggest methanogenesis occurs via at least two independent pathways involving methylamine and methylphosphonate transformations that, concomitantly to aerobic methane production, generate bioavailable nitrogen and phosphate, respectively. Methylphosphonate may be sourced from seawater continuously filtered by the sponge host. Methylamines may also be externally sourced or, alternatively, generated by a multi-step metabolic process where carnitine, derived from sponge cell debris, is transformed to methylamine by different sponge-hosted microbial lineages. Finally, methanotrophs specialized in pigment production, affiliated to the phylum Binatota, may provide a photoprotective function, closing a previously undescribed C 1 -metabolic loop that involves both the sponge host and specific members of the associated microbial community. Conclusion Given the global distribution of this ancient animal lineage and their remarkable water filtration activity, sponge hosted methane cycling may affect methane supersaturation in oxic coastal environments. Depending on the net balance between methanogenesis and methanotrophy, sponges may serve as marine sources or sinks of this potent greenhouse gas.