GH10 XynA is the main xylanase identified in the crude enzymatic extract of Paenibacillus sp. A59 when grown on xylan or lignocellulosic biomass

A novel bacterial isolate with polysaccharides degrading activity was identified as Paenibacillus sp., and named Paenibacillus sp. A59. Even though it is a strict mesophile, optimal xylanase activity of the crude enzymatic extract was achieved between 50 °C and 70 °C and more than 60% of the activity was retained after incubation for 48 h at 50 °C, indicating thermotolerance of the enzymes involved. The extract was also active on pre-treated sugarcane residue (SCR) and wheat straw, releasing xylobiose and xylose as the main products, therefore confirming its predominantly xylanolytic activity. By zymograms and mass spectrometry of crude enzymatic extracts of xylan or SCR cultures, a 32 kDa GH10 beta- 1,4- endoxylanase with xylanase and no CMCase activity was identified. We named this enzyme XynA and it was the only xylanase identified under both conditions assayed, suggesting that it is a good candidate for recombinant expression and evaluation in hemicelluloses deconstruction applications. Also, a protein with two S-layer homology domains (SLH) and a large uncharacterized C-terminal domain as well as an ABC substrate binding protein were identified in crude extracts of SCR cultures. We propose that Paenibacillus sp. A59 uses a system similar to anaerobic and other Gram positive bacteria, with SLH-domain proteins anchoring polysaccharide-degrading enzymes close to the membrane and the substrate binding protein assisting translocation of simple sugars to the cell interior.