Studies On Isolation, Structure Elucidation And Biological Activities Of Antibiotics From Paenibacillus Elgii B69

A bacterial strain B69, exhibiting promising antimicrobial activity against both Gram-positive, Gram-negative bacteria, and fungi, was isolated from the soil samples collected from the Tianmu Mountain National Natural Reserve. Based on the 16S rDNA sequence analysis along with phenotypical and biochemical characterization, this bacterium was identified as Paenibacillus elgii. Two antimicrobial compounds, named as Pelgipeptins A and B, were isolated from the culture medium using MCI GEL CHP20P column chromatography and HPLC methods. The molecular masses of Pelgipeptins A and B were 1072 and 1100 Da, respectively. The ESI-CID-MS and amino acid analysis suggested the tentative sequences of Pelgipeptin A (L-Dab-D-Val-L-Leu/Ile-L-Ser-Y1-L-Dab-L-Val-L-Dab-D-Phe-L-Leu/Ile) and Pelgipeptin B (L-Dab-D-Val-L-Leu/Ile-L-Ser-Y2-L-Dab-L-Leu/Ile-L-Dab-D-Phe-L-Leu/Ile), in which the structure of Y maybe fatty acid chains. When compared with the public Dab-containing antibiotics, Pelgipeptins were found to be structurally related to the members of the Polypeptin family. The molecular mass of Pelgipeptin B was identical to that of Permetin A, and their partial amino acid sequences were very similar, suggesting that they were probably the same compound. Furthermore, Pelgipeptin A was unequivocally characterized as a new antibiotic, as its structure was not identical to any public antibiotic.In this study, the stability, antimicrobial activity both in vitro and vivo of these antibiotics were also investigated. Stability analysis indicated the inhibitory activity of antibiotics was unaffected during exposure to 60℃for 2 h or a pH ranging from 1.0 to 8.0, however the activity was significantly reduced at pH 9.0 and 10.0, and totally lost at pH 11 and 12. Pelgipeptin A and B were active against all the tested strains and displayed strong antibacterial activity against drug-resistant strain Staphylococcus epidermidis CMCC 26069 (Ampicillin-resistant) with minimal inhibitory concen-tration (MIC) values of 3.12 and 0.78μg/ml respectively. This finding implied that Pelgipeptins have potential for biomedical use. Furthermore, these two antibiotics showed promising antifungal activity against several soil-borne fungal pathogens, having MIC values of 6.25-50μg/ml. In the vivo efficacy test, application of 250 μg/ml partial purified antibiotic (PPA) could effectively inhibit the development of sheath blight on rice, with approximately an 82% reduction in symptoms. Based on the strong antifungal activity both in vitro and vivo, Pelgipeptins might provide an alternative resource of chemical pesticides for the biocontrol of plant diseases.