Xylan Degradation in the Halotolerant Bacterium Bacillus altitudinis relies on glycosidic hydrolases from families 11 and 30

The breakdown of xylan, a major hemicellulose component, involves multiple xylanases.Bacillus altitudinis SRL571, a halotolerant endophytic bacterium, utilizes glucuronoxylan and xylose as its sole carbon and energy sources. Genome analysis revealed two sequences encoding putative secreted xylanolytic glycoside hydrolases: one from family 11 (BaGH11) and another from family 30, subfamily 8 (BaGH30). These genes are located in two distinct operons involved in xylan and xylose catabolism, a genomic configuration unique to this strain. Both enzymes are salt-tolerant and act as endoxylanases: BaGH11 releases mainly short-chain xylooligosaccharides (e.g., xylobiose) while BaGH30 produces medium-chain xylooligosaccharides. BaGH11 and BaGH30 act synergistically to hydrolyze glucuronoxylan into xylose and xylobiose, which are subsequently imported into cells via putative sugar transporters. This study elucidates the biocatalytic basis of xylan degradation in a halotolerant bacterium and highlights the importance of complementary enzyme activities for effective biomass degradation in saline environments.