The genome of Rhodothermus marinus DSM 4253 encodes six glycoside hydrolases (GH) classified under GH family 3 (GH3): Rm Bgl3A, Rm Bgl3B, Rm Bgl3C, Rm Xyl3A, Rm Xyl3B and Rm Nag3. The biochemical function, modelled 3D-structure, gene cluster and evolutionary relationships of each of these enzymes were studied. The six enzymes were clustered into three major evolutionary lineages of GH3: β- N -acetyl-glucosaminidases, β-1,4-glucosidases/β-xylosidases and macrolide β-glucosidases. The Rm Nag3 with additional β-lactamase domain clustered with the deepest rooted GH3-lineage of β- N -acetyl-glucosaminidases and was active on acetyl-chitooligosaccharides. Rm Bgl3B displayed β-1,4-glucosidase activity and was the only representative of the lineage clustered with macrolide β-glucosidases from Actinomycetes. The β-xylosidases, Rm Xyl3A and Rm Xyl3B, and the β-glucosidases Rm Bgl3A and Rm Bgl3C clustered within the major β-glucosidases/β-xylosidases evolutionary lineage. Rm Xyl3A and Rm Xyl3B showed β-xylosidase activity with different specificities for para -nitrophenyl ( p NP)-linked substrates and xylooligosaccharides. Rm Bgl3A displayed β-1,4-glucosidase/β-xylosidase activity while Rm Bgl3C was active on p NP-β-Glc and β-1,3-1,4-linked glucosyl disaccharides. Putative polysaccharide utilization gene clusters were also investigated for both R. marinus DSM 4253 and DSM 4252 T (homolog strain). The analysis showed that in the homolog strain DSM 4252 T Rmar_1080 ( Rm Xyl3A) and Rmar_1081 ( Rm Xyl3B) are parts of a putative polysaccharide utilization locus (PUL) for xylan utilization.
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Ara et al. (2020) studied this question.