Isolation of a novel gellan-depolymerizing Bacillus sp strain YJ-1

Abstract

A novel microorganism that could degrade high molecular weight gellan was screened and isolated from soil. On gellan plate, the microorganism grew well and completely liquefied the plate. The gellan-degrading microorganism was isolated by pure culture on glucose and nutrient agar medium afterwards. The 16S rDNA sequence analysis and biochemical tests using an API 50CHB/20E kit revealed that the strain belonged to Bacillus sp. The isolate, named as Bacillus sp. YJ-1, showed optimum gellan-degrading activity in 0.5% gellan medium at pH 7.5 and 37 degrees C. The activity was measured and evaluated by the thiobarbituric acid and thin-layer chromatography method. Mass spectrometry revealed that the major gellan-depolymerized product was an unsaturated tetrasaccharide consisting of Delta 4,5-glucuronic acid-(1 -> 4)-beta-D-glucose-(1 -> 4)-alpha-L-rhamnose-(1 -> 3)-beta-D-glucose, which is a dehydrated repeating unit of gellan, thus the enzyme was identified as gellan lyase. When the gellan was present in the medium, the gellan-degrading activity was much higher than that in glucose-grown cells. These results indicate that in the presence of gellan, Bacillus sp. YJ-1 is able to metabolize the gellan by inducing gellan-degrading enzymes that can degrade gellan into small molecular weight oligosaccharides, and then the gellan-depolymerized products are taken up by the cells and utilized by intracellular enzymes.