Peptidoglycan is the great success story of bacterial evolution. This mesh-like polymer of sugars and amino acids encases nearly every bacterial cell, protecting it from osmotic pressure and serving as the target of some of our most important antibiotics, from penicillin to vancomycin. Archaea, by contrast, were long thought to have abandoned peptidoglycan entirely, wrapping themselves in proteinaceous S-layers or pseudomembranes instead. Yet decades ago, researchers working on methanogenic archaea described a peptidoglycan-like polymer, dubbed pseudomurein, in a major clade of methane producers. Despite its early discovery, this archaeal peptidoglycan remained poorly characterized, largely because scientists lacked the dedicated analytical tools that transformed bacterial peptidoglycan research. Without enzymes capable of specifically degrading the polymer, its fine structure remained locked away.

The breakthrough came from an approach that mirrors the history of bacterial cell wall biology. In bacteria, enzymes called muramidases, which cleave the sugar backbone of peptidoglycan, proved indispensable for teasing apart wall architecture. The Pasteur-led team reasoned that archaea themselves, or the viruses that infect them, might harbor analogous hydrolases. Using a combination of bioinformatic screening and zymography, a technique that detects lytic activity directly in protein gels, the researchers identified eleven candidate hydrolases from M. smithii. Among these, one protein stood out: ArmA, a large multi-domain enzyme that proved to be the first glycosyl hydrolase specific for archaeal peptidoglycan.

What ArmA revealed when set loose on purified M. smithii cell walls was genuinely unexpected. The prevailing model, built on chemical analyses from the late 1970s and early 1980s, held that the glycan backbone of pseudomurein consisted of alternating N-acetylglucosamine and N-acetyltalosaminuronic acid residues. The new work shows that the reality is different. The glycan backbone comprises N-acetylglucosamine or N-acetylgalactosamine linked to a previously undescribed sugar, which the team has named N-acetylarmosamine. Even more strikingly, the glycan strands do not run with a uniform linkage pattern. Instead, they alternate between beta(1,4) and beta(1,3) glycosidic linkages, an arrangement that distinguishes archaeal peptidoglycan sharply from its bacterial counterpart, in which the backbone is stitched together exclusively with beta(1,4) bonds.

The peptide stems that cross-link the glycan strands also attach in an unusual way. In bacterial peptidoglycan, stem peptides are typically joined to the sugar backbone through standard amide bonds on the carboxyl groups of the constituent sugars. In the archaeal polymer, the researchers found that the stem peptide is attached by means of an amide bond to the succinyl group of N-acetylarmosamine, an architectural detail that had escaped earlier characterization. Mass spectrometry and nuclear magnetic resonance spectroscopy, applied to fragments released by enzymatic digestion, provided the structural evidence needed to establish these features with confidence, and the analysis was extended across diverse methanogens to confirm that the architecture is broadly conserved.

ArmA itself turned out to be a remarkably versatile molecular machine. The enzyme displays dual enzymatic activity, cleaving both the glycosidic linkages of the sugar backbone and the peptide crosslinks that hold the wall mesh together. This two-in-one capability makes it a uniquely powerful analytical reagent, comparable in impact to the muramidases that revolutionized the study of bacterial walls. Phylogenetic analyses added an evolutionary dimension to the story: ArmA homologues are restricted to archaea that actually possess peptidoglycan walls, suggesting that the enzyme co-evolved with the polymer it degrades. The team confirmed hydrolase activity across a range of methanogenic species, establishing ArmA and its relatives as a general toolkit for interrogating methanogen cell walls.

Perhaps the most biologically satisfying finding concerns what ArmA actually does inside the cell. Using antibodies raised against the protein, the researchers tracked ArmA’s localization through the M. smithii cell cycle with super-resolution microscopy. The enzyme forms a discontinuous ring-like structure precisely at the division plane, and as cytokinesis progresses, new rings appear in the prospective daughter cells at the sites where the next round of division will occur. This pattern strongly suggested a role in splitting the wall during cell division, and genetic experiments confirmed it. Deleting the armA gene in the thermophilic methanogen Methanothermobacter thermautotrophicus produced cells that failed to complete cytokinesis properly, forming elongated filaments. ArmA, in other words, is required to cleave archaeal peptidoglycan at the site of cell division, playing a role analogous to the autolysins that bacteria deploy to separate their daughter cells.

The implications of the work extend well beyond structural biology. Methanogens are ecologically and biotechnologically significant organisms: they dominate the archaeal component of the human gut microbiome, contribute substantially to methane emissions from livestock, and are increasingly explored as platforms for biotechnology. Because archaeal peptidoglycan is essential to the organisms that build it and is structurally distinct from bacterial peptidoglycan, the pathway and its enzymes represent an attractive target for targeted intervention. The authors note that a patent application covering the use of ArmA to regulate methanogen populations in industrial, agricultural and medical settings has been filed by Institut Pasteur, underscoring the applied potential of the discovery. Selectively disrupting the walls of gut methanogens, for instance, could offer new strategies for modulating the archaeome in contexts ranging from digestive health to methane mitigation in ruminants.

Scientifically, the study marks a turning point in how the field approaches archaeal cell biology. For decades, archaeal peptidoglycan was a curiosity, described in classic biochemical studies but largely inaccessible to modern genetic and cell biological analysis. ArmA changes that calculus entirely. Just as muramidases enabled the dissection of bacterial wall architecture, muropeptide profiling and hydrolase genetics in bacteria, this archaeal enzyme opens the door to biochemical and genetic interrogation of methanogen cell-wall biology with the same rigor. The work also carries evolutionary weight: peptidoglycan is often invoked in debates about the deep ancestry of the two prokaryotic domains, and a precise, experimentally grounded picture of the archaeal polymer will inform models of how cell-wall biochemistry evolved and diversified across the tree of life.

What began as a search for a molecular tool ended as a revision of a textbook paradigm. A 50-year-old model of archaeal peptidoglycan structure has given way to a new one, built on an alternating-linkage glycan backbone, an unprecedented sugar called N-acetylarmosamine, and a stem-peptide attachment chemistry unique to the archaeal domain. And the enzyme that made the discovery possible turns out to be no mere laboratory reagent but a bona fide division machine, choreographed to the cell cycle and essential for the propagation of some of the most consequential microbes on Earth. For a polymer that spent half a century in the shadows, archaeal peptidoglycan has suddenly become one of the most exciting molecules in microbiology.

Subject of Research: Structure and cell division role of archaeal peptidoglycan in methanogenic archaea

Article Title: A methanogen hydrolase reveals the structure of archaeal peptidoglycan

Article References: Smith, R., Pende, N., Rifflet, A., Taib, N., Witwinowski, J., Martin-Gallausiaux, C., Cornilleau, C., Garcia, P. S., Villa, R., Douché, T., Matondo, M., Majrouh, M., Reichelt, R., Grohmann, D., Tripp, P., Albers, S.-V., Borrel, G., Rittmann, S. K.-M. R., Sartori-Rupp, A., … Gribaldo, S. (2026). A methanogen hydrolase reveals the structure of archaeal peptidoglycan. Nature. https://doi.org/10.1038/s41586-026-11028-y

Image Credits: AI Generated

DOI: 10.1038/s41586-026-11028-y

Keywords: archaea, peptidoglycan, methanogens, cell wall, ArmA hydrolase, Methanobrevibacter smithii, pseudomurein, N-acetylarmosamine, cytokinesis, glycosyl hydrolase, human gut microbiome, cell biology