Degradation of beechwood xylan using food-grade bacteria-like particles displaying β-xylosidase from Limosilactobacillus fermentum

The display of enzymes on bacterial surfaces is an interesting approach for immobilising industrially important biocatalysts. In recent years, non-recombinant surface display using food-grade bacteria, such as lactic acid bacteria (LAB), have gained interest because of their safety, simplicity, and cost-effectiveness. β-Xylosidase is one of the many biocatalytic enzymes targeted for immobilisation due to its key role in the complete saccharification of lignocellulosic biomass, including xylan hemicellulose. Recently, the xylose-tolerant β-xylosidase, LfXyl43, was identified in Limosilactobacillus fermentum. LfXyl43 is capable of producing xylose from the degradation of xylo-oligosaccharides (XOS) and beechwood xylan. This study aimed to immobilise this new biocatalyst on the surface of LAB-derived bacteria-like particles (BLP) and investigate its applicability and reusability in the degradation of xylan hemicellulose. Additionally, the influence of the anchor position and the presence of linker peptides on the display and activity of the β-xylosidase was investigated. Four expression vectors were constructed to express different anchor-xylosidase fusion proteins. Upon expression and purification, all anchor-xylosidase fusion proteins were active towards the artificial substrate p-nitrophenyl-β-D-xylopyranoside. In addition, all anchor-xylosidase fusion proteins were successfully displayed on the surface of BLP. However, only the β-xylosidases with linker peptide showed hydrolytic activity after immobilisation on BLP. BLP displaying β-xylosidases demonstrated high activity against XOS and beechwood xylan, thereby producing high amounts of xylose. Moreover, the immobilised enzyme demonstrated reusability across several bioconversion cycles. Overall, this study highlights the potential industrial application of surface-displayed β-xylosidase for the effective degradation of lignocellulosic biomass.