Identification of a Novel Fungus, Leptosphaerulina chartarum SJTU59 and Characterization of Its Xylanolytic Enzymes

Qiong Wu,Jie Chen,Tailong Zhang,Yaqian Li,Shigang Gao,Meng Wang,Yingying Li,Eugene A Permyakov

doi:10.1371/journal.pone.0073729

Abstract

Xylanolytic enzymes are widely used in processing industries, e.g., pulp and paper, food, livestock feeds, and textile. Furthermore, certain xylanotic enzymes have demonstrated the capability to improve the resistance and immunity of plants. Screening of high-yield microbial xylanolytic enzyme producers is significant for improving large-scale cost-effective xylanolytic enzyme production. This study provided new evidence of high-level xylanolytic enzyme production by a novel fungus, designated Leptosphaerulina chartarum SJTU59. Under laboratory conditions, L. chartarum SJTU59 produced xylanolytic enzymes of up to 17.566 U/mL (i.e., 878.307 U/g substrate). The enzyme solution was relatively stable over a wide range of pH (pH 3.0 to pH 9.0) and temperature (40°C to 65°C) while showing high resistance to the majority of metal ions tested. Composition analysis of the hydrolytic products of xylan showed sufficient degradation by xylanolytic enzymes from L. chartarum SJTU59, mainly the monosaccharide xylose, and a small amount of xylobiose were enzymatically produced; whereas in the presence of sufficient xylan substrates, mainly xylooligosaccharides, an emerging prebiotic used in food industry, were produced. In addition, the xylanolytic enzyme preparation from L. chartarum SJTU59 could initiate tissue necrosis and oxidative burst in tobacco leaves, which may be related to enhanced plant defense to adversity and disease. L. chartarum SJTU59 possessed a complex xylanolytic enzyme system, from which two novel endo-β-1,4-xylanases of the glycoside hydrolase (GH) family 10, one novel endo-β-1,4-xylanase of the GH family 11, and one novel β-xylosidase of the GH family 43 were obtained via rapid amplification of complementary DNA ends. Given the high yield and stable properties of xylanolytic enzymes produced by L. chartarum SJTU59, future studies will be conducted to characterize the properties of individual xylanolytic enzymes from L. chartarum SJTU59. xylanolytic enzymes-encoding gene(s) of potential use for industrial and agricultural applications will be screened to construct genetically engineered strains.

Highlights

IntroductionAn abundance of diverse xylanolytic enzymes are currently known to catalyze the hydrolysis of xylan
Xylanolytic enzymes are an extensive group of enzymes (EC 3.2.1.x) [1]
Considering the potential limitation of selected primers [30,31], we believe that undetected gene(s) are possibly present in the xylanolytic enzyme system of L. chartarum SJTU59

Summary

Introduction

An abundance of diverse xylanolytic enzymes are currently known to catalyze the hydrolysis of xylan. These xylanolytic enzymes are generally classified using standard means based on primary structure comparisons of catalytic domains and enzymes in families of related sequences [2]. Only members of GH families 5, 7, 8, 10, 11, and 43 contain truly distinct catalytic domains with a demonstrated xylanolytic enzyme activity. Xylanolytic enzymes belonging to GH families 5, 7, and 8 have been studied to a lesser extent. Endo-b-1,4-xylanase, which catalyzes the hydrolysis of b1,4-xylosidic linkages of xylan backbone, and b-xylosidase, which catalyzes the hydrolysis of nonreducing end-xylose residues from xylooligosaccharides, both belong to the group of xylanolytic enzymes [1]

Methods

Results

Conclusion