Paenibacillus xanthanilyticus sp. nov., a xanthan-degrading bacterium isolated from soil.

A xanthan-degrading bacterium, strain AS7T, was isolated from soil and its taxonomic position was determined using a polyphasic approach. Strain AS7T was a Gram-stain-variable, spore-forming, motile, aerobic, rod-shaped bacterium. Phylogenetic analysis based on 16S rRNA gene sequence analysis revealed that strain AS7T belongs to the genus Paenibacillus, sharing the highest level of sequence similarity with Paenibacillus phyllosphaerae PALXIL04T (98.0 %). The cell-wall peptidoglycan contained meso-diaminopimelic acid. MK-7 was the dominant isoprenoid quinone and the major fatty acid was anteiso-C15 : 0. Polar lipids consisted of diphosphatidylglycerol, phosphatidylglycerol, phosphatidylethanolamine and two unknown phospholipids. These chemotaxonomic characteristics were consistent with the isolate belonging to the genus Paenibacillus. The G+C content of the genomic DNA was 51.0 mol% and the DNA-DNA hybridization value between strain AS7T and P. phyllosphaerae PALXIL04T was only 14.4±2.5 %. On the basis of phylogenetic analyses, phenotypic and chemotaxonomic characteristics, and DNA-DNA relatedness value, strain AS7T represents a novel species of the genus Paenibacillus, for which the name Paenibacillus xanthanilyticus sp. nov. is proposed. The type strain is AS7T (=IBRC M 10987T=LMG 29451T).

Production of Xanthanases by Paenibacillus spp.: Complete Xanthan Degradation and Possible Applications.

Background: A number of microorganisms and their enzymes have been reported as xanthan depolymerizers. Paenibacillus species are well-known polysaccharide hydrolyzing bacteria. However, Paenibacillus alginolyticus and Paenibacillus sp. XD are the only species in the genus which are now known to degrade xanthan. Objectives: Complete biodegradation of the xanthan exopolysaccharide is a rarely found capability among microorganisms. The aim of this study is to survey xanthanase producing bacteria with an appropriate bioactivity for the biopolymer degradation under different environmental conditions. Materials and Methods: The bacteria were isolated based on viscosity reduction of the xanthan solution. Bacterial isolates were identified using rep-PCR (repetitive element-based genomic fingerprinting) and 16S rDNA sequencing. Xanthanases were identified using rep-PCR (repetitive element-based genomic fingerprinting) and 16S rDNA sequencing. Xanthanases were characterized by measuring their activity at different temperatures, pH values, and NaCl concentrations. Degradation of other polysaccharides and xanthan degradation products were investigated based on the screening plate method and TLC (thin-layer chromatography), respectively. Results:Six isolates from different Paenibacillus species with a complete xanthan degrading capability were isolated from Urmia Lake. Phylogenetic analysis placed these strains within the genus Paenibacillus with the closest relatives that were found to be P. nanensis, P. phyllosphaerae, P. agaridevorans, P. agarexedens, and P. taohuashanense. These isolates displayed different levels of the xanthan biodegradation activity in temperatures ranging from 15 to 55°C and pH values from 4 to 11. Xanthanolytic activity was generally prevented in presence of NaCl (> 0.1 mol.L-1). Furthermore, the isolated Paenibacillus spp. could degrade several other polysaccharides including xylan, CMC (carboxymethyl cellulose), starch, alginate, and pectin. Conclusion: Novel strains of the six different Paenibacillus species that were introduced in the present study are able to produce xanthanases with interesting characteristics. In light of the results from this study, special applications, particularly in healthcare, medicine, and the environment is hereby proposed for these enzymes.