The Preliminary Isolation Of An Antibacterial Strain SDLH-I From Oxya Chinensis

In the previous work, we found a new antibacterial substance existed in foregut of an Oxya chinensis, an incomplete metamorphosis insect. The crude extract of Oxya chinensis as the raw material was used to screen strains of producing antibacterial peptides. Based on colony morphological character and antibacterial activity, 17 strains were selected in this work.A strain, named SDLH-I with the higher antibacterial activity, was carried on the further work. The strain SDLH-I belongs to a bacillus bacterium with a gram-negative, no spores and round flagella. The optimal condition for producing antibacterial peptides was incubated in beef extract peptone medium at pH 7.5, 37°C for 16h. The result shows that 4.1-6.5 kDa antibacterial substances separated from the crude extract described above could efficiently kill Gram-positive bacteria (Staphylococcus aureus, Bacillus subtilis and Micrococcus luteus), but no any activity for Gram--negative bacteria (Escherichia coli) or fungi (Saccharomyces cerevisiae).As we know, 16S rDNA sequence is an important standard for identifying and classifying bacteria. Therefore, the 16S rDNA of SDLH-I was amplified by PCR with its colony as the template and the PCR product was inserted into T-vector and sequenced as well. The strain SDLH-I may be named Serratia Bizio. sp. Meanwhile, a phylogeny of strains was established.