Exploration of Novel Extracellular Xylanase-Producing Lactic Acid Bacteria from Plant Sources

Xylanases play a crucial role in bio-transforming sustainable agricultural polymers into xylose-based oligosaccharides, which have great potential in various biotechnology applications. Nevertheless, the application of bacterial xylanase is hindered by the high cost of developing recombinant bacteria to overcome the low activity and narrow pH stability. Considerable efforts have been made to discover and explore new wild bacterial strains that produce highly effective and environmentally sustainable extracellular xylanase enzymes for various targeted biotechnological and industrial applications. Lactic acid bacteria (LAB) have recently been proven to be versatile producers of extracellular hydrolytic enzymes. Therefore, this study aimed to isolate and characterise extracellular xylanase-producing LAB (EXLAB) from plant sources. The specific extracellular xylanase activity was determined across a wide pH range, from acidic to alkaline. Subsequently, the expression of xylanase genes of EXLAB grown under acidic and alkaline conditions was determined by quantitative reverse transcription polymerase chain reaction. A total of 45 putative LAB were isolated from radish, gundelia and rhubarb plants. They were identified by phenotypic and genotypic approaches. However, only 15 LAB isolates were confirmed as EXLAB. Weissella confusa and Pediococcus pentosaceus were the most common species among the identified EXLAB. The XylW (~196 bp) and XylP (189 bp) xylanase genes were then amplified from W. confusa and P. pentosaceus, respectively. P. pentosaceus G4 demonstrated the most versatile extracellular xylanase production that was active from pH 5 to pH 8. However, a significant increase in extracellular xylanase gene expression (13.45-fold) at pH 5 was noted as compared to pH 8. Similarly, P. pentosaceus G4 also exhibited the highest extracellular xylanase activity (0.88 U/mg) at pH 5. This study reveals the potential of P. pentosaceus G4 as an eco-friendly and novel extracellular xylanase producer possessing broad pH stability. The robust gene expression and activity of extracellular xylanase imply P. pentosaceus G4 is a promising candidate for sustainable enzymatic processes essential for the environmentally friendly enzymatic reactions and applications.