Characterization of xylan degradation systems in streptomyces

Abstract

Plant biomass serves as a carbon and energy source for Streptomyces spp. which secrete degradative enzymes capable of breaking down the complex plant biomass into simple saccharides. Hemicellulose is a major component of plants and is composed of five and six carbon sugars, such as xylose and glucose. Enzymatic degradation of hemicellulose to obtain desired sugars has been a cornerstone of many industries, as well as the subject of worldwide research for additional sources of efficient enzymes for substrate conversion. In this study, environmentally-derived Streptomyces isolates were screened for their ability to hydrolyze oat-spelt and birchwood xylan in agar-based high throughput activity screens. Of the isolates tested, eight displayed high levels of substrate-degrading activity and were chosen for further characterization which included 16S rRNA gene analysis, microscopic analysis from both liquid and agar grown cultures, xylanase-specific activity, lignin peroxidase production and indole acetic acid production.Qualitative assessment of extracellular lactone signalling for all eight isolates was also performed. Putative lactone signalling was observed for Streptomyces isolates JLS1-C4, JLS1-A6, JLS2-D6 and KT1-B1 which exhibited xylanase-specific activities of 0.622 μmol/min/mg, 0.0243 μmol/min/mg, 0.721 μmol/min/mg, and 0.706 μmol/min/mg respectively. Streptomyces isolates JLS1-F12 and JLS1-C12 did not exhibit lactone signalling but did exhibit xylanase-specific activities of 0.125 μmol/min/mg and 0.0688 μmol/min/mg respectively. No xylanase-specific activity was detected for isolates JLS2- C7 and KT1-B8; however lactone signalling was observed for isolate KT1-B8. Streptomyces isolate JLS1-A6 degraded birchwood xylan optimally at pH 4 and 28°C with a maximal xylanase activity of 1.56 x10-3 μmol/min/mg.