Functional exploration of Pseudoalteromonas atlantica as a source of hemicellulose-active enzymes: Evidence for a GH8 xylanase with unusual mode of action

•Pseudoalteromonas atlantica produced a high diversity of polysaccharide-degrading enzymes.•The marine bacterium Pseudoalteromonas atlantica secreted enzymes active towards hemicelluloses from terrestrial plants.•β-xylosidase, α-arabinofuranosidase and acetylesterase activities were evidenced in the secretome of Pseudoalteromonas atlantica.•The GH8 protein present in Pseudoalteromonas atlantica genome is a xylanase with unusual product profile. To address the need for efficient enzymes exhibiting novel activities towards cell wall polysaccharides, the bacterium Pseudoalteromonas atlantica was selected based on the presence of potential hemicellulases in its annotated genome. It was grown in the presence or not of hemicelluloses and the culture filtrates were screened towards 42 polysaccharides. P. atlantica showed appreciable diversity of enzymes active towards hemicelluloses from Monocot and Dicot origin, in agreement with its genome annotation. After growth on beechwood glucuronoxylan and fractionation of the secretome, a β-xylosidase, a α-arabinofuranosidase and an acetylesterase activities were evidenced. A GH8 enzyme obtained in the same growth conditions was further cloned and heterologously overexpressed. It was shown to be a xylanase active on heteroxylans from various sources. The detailed study of its mode of action demonstrated that the oligosaccharides produced carried a long tail of un-substituted xylose residues on the reducing end.