de Araújo Butarelli, Ana Carolina

Abstract Deception Island fumaroles in Antarctica represent rare environments where extreme heat intersects with cryospheric and marine conditions, creating remarkable environmental gradients. From the near-boiling sediments, we reconstructed a high-quality metagenome-assembled genome (MAG) affiliated with the Pyrodictiaceae. Phylogenomic analyses revealed that this genome, proposed to represent Ca. Pyroantarcticum pellizari, forms a distinct lineage separated from known genera in the family. Functional annotation uncovered a versatile metabolic repertoire, including pathways for sulfur and nitrogen cycling, peptide and amino acid transport, and mixotrophic energy conservation. Stress-response systems such as reverse gyrase, thermosome, and small heat-shock proteins were complemented by lineage-specific genes related to membrane stability, metal detoxification, and Pyrodictiaceae-specific cannulae. These adaptations likely support survival under sharp temperature gradients, hydrogen sulfide emissions, and high metal concentrations at the volcanic–cryosphere–marine interface. Our findings expand the phylogenetic and ecological scope of Pyrodictiaceae, highlighting Antarctic marine volcanoes as unique refuges for hyperthermophiles and as valuable models for investigating life’s habitability under extreme temperatures.

AbstractRecent discoveries of aerobic methanotrophs in non-seep carbonate-rich environments in the deep sea suggest that these organisms may persist as part of the rare biosphere. Recovering rare, active methanotrophs through targeted culturing is essential for understanding their persistence under the oligotrophic non-seep conditions, and for uncovering their genomic adaptations related to the survival in energy-limited ecosystems. In our study, using metagenomic analysis of enrichment cultures from the Alpha Crucis Carbonate Ridge, we discoveredMethylotuvimicrobium crucissp. nov., a novel methanotroph representing the rare biosphere in native sediments. Phylogenomic analysis revealed <95% ANI to described species, with genomic evidence of deep-sea specialization including: (1) stress adaptation through cold-shock proteins (CspA) and DNA repair systems (UvrD/LexA), (2) metabolic versatility via complete methane oxidation(pmoABC), nitrogen fixation (nifHDK), and sulfur cycling (sox/sqr) pathways, and (3) niche partitioning through biofilm formation (GGDEF/EAL) and heavy metal resistance (CopZ/CzcD). Comparative genomics identified a 1,234-gene deep-sea core shared withM. sp. wino1, enriched in mobile elements (TnpA, prophages) suggesting horizontal gene transfer drives adaptation. While undetectedin situamplicon surveys,M. crucisexhibited rapid enrichment under methane availability, demonstrating its role as a latent methane filter. These findings contribute for the understanding of the ecological significance of aerobic methanotrophs in deep-sea systems, revealing how rare microbial taxa with genomic plasticity have the potential to influence biogeochemical cycling in deep carbonate-rich environments.