Journal ArticleCharacterization of the thermophilic xylanase <scp>Fsa02490Xyn</scp> from the hyperthermophile <i>Fervidibacter sacchari</i> belonging to glycoside hydrolase family 10Torosian, Nicole [School of Life Sciences University of Nevada, Las Vegas NV USA]; Covington, Jonathan K [School of Life Sciences University of Nevada, Las Vegas NV USA]; Cook, Allison M [School of Life Sciences University of Nevada, Las Vegas NV USA]; Nou, Nancy O [School of Life Sciences University of Nevada, Las Vegas NV USA] (ORCID:0000000347588131); Palmer, Marike [Department of Microbiology University of Manitoba Winnipeg Canada]; Mewalal, Ritesh [US Department of Energy Joint Genome Institute Lawrence Berkeley National Laboratory CA USA]; Harmon‐Smith, Miranda [US Department of Energy Joint Genome Institute Lawrence Berkeley National Laboratory CA USA] (ORCID:0000000239801820); Blaby, Ian K [US Department of Energy Joint Genome Institute Lawrence Berkeley National Laboratory CA USA]; Cheng, Jan‐Fang [US Department of Energy Joint Genome Institute Lawrence Berkeley National Laboratory CA USA] (ORCID:0000000173157613); Hess, Matthias [Department of Animal Science, College of Agricultural and Environmental Sciences University of California, Davis CA USA] (ORCID:0000000303210380); Hedlund, Brian P [Nevada Institute of Personalized Medicine University of Nevada, Las Vegas NV USA] (ORCID:0000000185300448)<sec><label/><p><italic>Fervidibacter sacchari</italic>is an aerobic hyperthermophile belonging to the phylum<italic>Armatimonadota</italic>that degrades a variety of polysaccharides. Its genome encodes 117 enzymes with one or more annotated glycoside hydrolase (GH) domain, but the roles of these putative GHs in polysaccharide catabolism are poorly defined. Here, we describe one<italic>F. sacchari</italic>enzyme encoding a GH10 domain, Fsa02490Xyn, that was previously shown to be active on<italic>Miscanthus</italic>, oat β‐glucan, and beech‐wood xylan, with optimal activity at 90–100 °C. We show that Fsa02490Xyn is also active on birch‐wood xylan and gellan gum. The pH range on beech‐wood xylan was 4.5 to 9.5 (pH_opt7.0–8.0). Fsa024940Xyn had a<italic>K</italic>_mof 2.375 m<sc>m</sc>,<italic>V</italic>_maxof 1250 μ<sc>m</sc>·min⁻¹, and<italic>k</italic>_cat/<italic>K</italic>_mof 1.259 × 10⁴ s⁻¹·<sc>m</sc>⁻¹when using a<italic>para</italic>‐nitrophenyl‐𝛽‐xylobioside assay. A phylogenetic analysis of GH10 family enzymes revealed a large clade of enzymes from diverse members of the class<italic>Fervidibacteria</italic>, including Fsa02490Xyn and a second enzyme from<italic>F. sacchari</italic>, with apparent horizontal gene transfer within<italic>Fervidibacteria</italic>and between<italic>Fervidibacteria</italic>and thermophilic<italic>Bacillota</italic>. This study establishes Fsa02490Xyn as a hyperthermophilic GH10 enzyme with endo‐β‐1,4‐xylanase activity and identifies a large clade of homologous GH10 enzymes within the class<italic>Fervidibacteria</italic>.</p></sec> <sec><label/><p><boxed-text content-type='box' position='anchor'><caption><title>Impact statement</title></caption><p>The depolymerization of xylan at high temperatures is important because this process limits the degradation of polysaccharides in nature and the synthesis of biofuels from plant wastes. Our study is also important because<italic>F. sacchari</italic>is one of only a few cultivated members of the<italic>Armatimonadota</italic>, which are polysaccharide‐degradation specialists.</p></boxed-text></p></sec>John Wiley & Sons Ltd.2025-10-0110650800FEBS Open Bio15101629 to 16422211-5463https://doi.org/10.1002/2211-5463.700721757316; 2244087National Science Foundation