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#pseudomurein

3 public questions tagged with this topic.

Microbial Physiology

Which archaeal species contains pseudomurein in its cell wall?

Distribution of pseudomurein within Archaea is limited to certain methanogenic euryarchaeota that build rigid wall sacculus, whereas many other archaea rely solely on proteinaceous S-layers. Methanobrevibacter species, including human commensal Methanobrevibacter smithii and rumen isolate Methanobrevibacter ruminantium within order Methanobacteriales, synthesize pseudomurein composed of N-acetylglucosamine and N-acetyltalosaminuronic acid linked beta-1,3 and crosslinked with tetrapeptides containing L-amino acids. Related genera like Methanobacterium and Methanothermobacter share this trait, distinguishing them from methanococci and methanosarcinales that lack walls. Sulfolobus, a crenarchaeon, possesses S-layer and tetraether lipids but not pseudomurein. Thermococcus, also euryarchaeon but within Thermococcales, possesses only S-layer or glycoprotein sheath. Thus among choices presented, Methanobrevibacter clearly contains pseudomurein, exemplifying lineage-specific wall innovation, while statement that all listed genera possess it would be incorrect because envelope diversity across archaea is extensive and pseudomurein evolved only within methanobacteriales and related orders. Interestingly, Methanobacteriales also produce unique coenzymes such as coenzyme M and methanofuran essential for methanogenesis, linking wall chemistry with specialized metabolism, and environmental surveys detect pseudomurein-encoding genes only within this lineage, confirming narrow distribution that supports using pseudomurein as chemotaxonomic marker for this group.

Ref: Kandler, Microbiol Sci 1982, Pseudomurein Distribution; Doddema et al., Int J Syst Bacteriol 1982, Methanobrevibacter.

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Microbial Physiology

Which glycosidic bond is found in the pseudomurein of archaea?

Glycosidic bond specificity determines susceptibility to host defenses and bacteriophages. Bacterial peptidoglycan uses beta-1,4 linkages between N-acetylglucosamine and N-acetylmuramic acid, a substrate efficiently cleaved by hen egg white lysozyme and human lysozyme in tears and mucus, which hydrolyzes between C1 of MurNAc and C4 of GlcNAc. Archaeal pseudomurein in methanogens such as Methanobacterium and Methanobrevibacter employs beta-1,3 linkage between N-acetylglucosamine and N-acetyltalosaminuronic acid. This change in linkage position alters orientation of sugar residues and active site complementarity, rendering bond refractory to lysozyme and to many bacterial autolysins that recognize beta-1,4. Alpha-linked variants such as alpha-1,4 found in starch and alpha-1,6 in glycogen are characteristic of storage polysaccharides, not wall polymers. Beta-1,3 linkage also affects cell wall flexibility and recognition by innate immune lectins. Hence presence of beta-1,3 rather than beta-1,4 is diagnostic feature underlying lysozyme resistance of pseudomurein-containing archaea and informs use of pseudomurein-specific endopeptidases like PeiW. Structural modeling demonstrates altered distance between anomeric carbons, affecting hydrogen bonding network that stabilizes wall, and this change has biotechnological implication because pseudomurein-specific hydrolases are used as tools for archaeal cell wall disruption in laboratories studying methanogenesis and for controlling bloating in ruminant animals.

Ref: Sekh et al., Extremophiles 2020, Pseudomurein Linkages; Leahy et al., Front Microbiol 2020, Archaeal Wall.

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Microbial Physiology

In the pseudomurein layer, which sugar replaces N-acetylmuramic acid (NAM) found in bacterial peptidoglycan?

Pseudomurein represents fascinating case of convergent evolution where archaeal methanogens assemble wall polymer with superficial resemblance to bacterial peptidoglycan but distinct sugar composition rendering it insensitive to many antibacterial agents. In bacterial murein, alternating N-acetylglucosamine (NAG) and N-acetylmuramic acid (NAM) linked beta-1,4 carry lactyl ether with short peptide containing D-amino acids. Archaeal pseudomurein replaces NAM with N-acetyl-D-talosaminuronic acid, abbreviated NAT, which is N-acetylglucosamine epimer bearing carboxyl group at different position and lacking D-lactyl substituent. NAT is generated through separate biosynthetic pathway, providing similar backbone function but altered stereochemistry. Lipoarabinomannan is mycobacterial glycolipid, not part of pseudomurein. This substitution, combined with use of L-glutamate, L-alanine, and L-lysine in interpeptide bridges, makes wall resistant to lysozyme that specifically recognizes NAM, and to penicillin which targets D-Ala-D-Ala motifs. Understanding NAT replacement clarifies why archaeal wall inhibitors require different targets and highlights divergence of glycosyltransferase evolution. Comparative genomics indicates distinct glycosyltransferase families synthesize NAT-containing precursors, and structural studies of NAT reveal altered chair conformation due to axial carboxyl group, influencing polymer packing and crosslink spacing, properties exploited for development of lytic enzymes used for selective lysis of methanogens in anaerobic digestion studies.

Ref: Kandler & Hippe, Arch Microbiol 1977, Pseudomurein Sacculus; Evren et al., J Bacteriol 2022, Pseudomurein Chemistry.

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