Biodiversity of thermotolerant xylanse-producing bacteria from soil in Nan province

Abstract

Isolation and screening of thermotolerant xylanase producing bacteria, sixty isolates were isolated from soil samples collected in NAN province. On the basis of their phenotypic and chemotaxonomic characteristics, DNA-DNA similarity and the phylogenetic analysis using 16S rDNA sequences, 25 isolates were identified as Microbacterium, 20 as Paenibacillus, 8 as Bacillus, 2 as Rhodococcus, 3 as Cohnella, 1 as Pseudoxanthomonas and 1 as Cupriavidus. The tested isolates of Paenibacillus, Bacillus, Rhodococcus, Cohnella contained meso-diaminopimelic in cell wall-peptidoglycan. The DNA G+C contents of Microbacterium, Pseudoxanthomonas and Cupriavidus isolates ranged from 70.9 to 71.4 mol%. The DNA G+C contents of Paenibacillus, Rhodococcus, and Cohnella isolates ranged from 41.7 to 61.6 mol%. Bacillus isolates contained 36-43.9 mol% of the DNA G+C content. Predominant menaquinones (MK) of the tested isolates in Microbacterium was MK11 and MK-12; Paenibacillus, Bacillus, and Cohnella were MK-7, and Rhodococcus was MK-8 (H2). The tested isolates of Pseudoxanthomonas and Cupriavidus contained ubiquinone with eight isoprenoid units (Q-8). This study, the known species were identified as Microbacterium barkeri (22 isolates), Paenibacillus favisporus (1 isolate), P. naphthalenovorans (1 isolate); Bacillus funiculus (6 isolates), and B. niabensis (1 isolate); Rhodococcus rhodochrous (2 isolates), Pseudoxanthomonas suwonensis (1 isolate), Cupriavidus gilardii (1 isolate) based on 99.0 to 99.8% similarity of 16S rDNA sequences. The novel species were found in Paenibacillus (10 new species) and Cohnella (3 new species) that they were differentiated from the type strains by several phenotypic characteristics and 16S rDNA sequence similarity (93.9 to 99.2 %). Among 60 isolates screened, a maximum xylanolytic activity exhibited 3.5 cm in diameter of clear zone. The isolate S3-4A identified as a new species of Paenibacillus was selected for xylanase optimization. This isolate produced 0.43 units of xylanase/ ml of culture broth when grown in XC medium containing (w/v) 1.0% oat spelt xylan, 0.5% peptone, 0.1 % yeast extract, 0.4% K2HPO, and 0.05% MgSO4.7H2O at 55 °C, pH 7.5 for 5 days. Optimum activity of this enzyme was at 50°C and pH 7, and was highly stable at 35-50°C .