Identification And Characterization Of A Strain Producing Xanthomonas Oryzae

Combination of cylinder plate method and liquid fermentation was applied, with the Escherichia coli, Staphylococcus aureus and Candida albicans as the test microorganisms, to screen the bacteria which can produce anti-bacterial bioactive substance from bacteria resistant to fosfomycin.At last, bacterium HF-1127 was obtained as the objective strain. Antibacterial spectrum investigation showed that the strain HF-1127 had strong activity against Escherichia coli and Staphylococcus aureus. It also had activity against other pathogenic bacteria to some extent, such as pseudomonas aeruginosa, Salmonella Typhimurium and Serratia marcescens. No inhibition activity against fungi was found.The investigation of its formal cultural and physiological characteristics indicated that Strain HF-1127 had the same characteristics with Luteimonas sp.. Comparison of its 16S rDNA sequence with the data in Genbank, showed the similarity of 95%-99% between this strain and Luteimonas sp.. Phylogenetic tree based on the similarity was established and the analysis confirmed that the strain had the closest relationship with Luteimonas sp. CHNTR51. Finally the strain HF-1127 was identified to be a Luteimonas with the characteristic of anti-bacterial activity.The results showed that the suitable culture medium was a liquid medium (glucose 20g, beef extract 8g, yeast extract 5g), the optimum culture conditions were 28℃, pH7.0, and 8%(v/v) of inoculated volume, and enlargement of the aerating quantity was beneficial to generating the anti-bacterial substance. The anti-bacterial activity was increased with cultivation time, the maximum of bacterial concentration occurred after cultured 18h, but the peak value of anti-bacterial activity appeared at 24 hours. Thereafter, with the culture time was increased, the inhibitory activity was decreased gradually.Bioactive substance was obtained from extracts of fermentation supernatant of the strain HF-1127. We also conducted the preliminary study on physico-chemical property of the bioactive products:the stability inspection, pH chromatograph and paper chromatograph experiments. These results showed the basic physico-chemical property of the bioactive products and founded the preliminary techniques of separation.The method for isolating active substance from fermentation supernatant by iron-exchange resin was preliminarily studied. The suitable ion-exchange resin is D113, a weakly acidic cation exchange resin. The breakthrough curve and adsorption rate curve were measured and 2% ammonia as the suitable eluant was found.