Shumei Zhang

Purification and characterization of a novel antifungal protein from Bacillus subtilis strain B29

An antifungal protein was isolated from a culture of Bacillus subtilis strain B29. The isolation procedure comprised ion exchange chromatography on diethylaminoethyl (DEAE)-52 cellulose and gel filtration chromatography on Bio-Gel® P-100. The protein was absorbed on DEAE-cellulose and Bio-Gel® P-100. The purified antifungal fraction was designated as B29I, with a molecular mass of 42.3 kDa by sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE), pI value 5.69 by isoelectric focusing (IEF)-PAGE, and 97.81% purity by high performance liquid chromatography (HPLC). B29I exhibited inhibitory activity on mycelial growth in Fusarium oxysporum, Rhizoctonia solani, Fusarium moniliforme, and Sclerotinia sclerotiorum. The 50% inhibitory concentrations (IC50) of its antifungal activity toward Fusarium oxysporum and Rhizoctonia solani were 45 and 112 μmol/L, respectively. B29I also demonstrated an inhibitory effect on conidial spore germination of Fusarium oxysporum and suppression of germ-tube elongation, and induced distortion, tumescence, and rupture of a portion of the germinated spores.

Isolation and characterization of antifungal lipopeptides produced by endophytic Bacillus amyloliquefaciens TF28

Bacillus amyloliquefaciens TF28, an endophytic bacterium isolated from soybean root, showed strong antifungal activity in vitro. In this study, crude lipopeptides were extracted with methanol from the precipitate by adding concentrated HCl to culture filtrate. They exhibited highest antifungal activity against the rice bakanae fungus Fusarium moniliforme. Besides F. moniliforme, the crude lipopeptides also inhibited the growth of other phytopathogens such as Botrytis cinerea, Fusarium oxysporum etc. Microscopic analysis found that the crude lipopetides distorted hyphae and spore of F. moniliforme. The crude lipopetides were very stable to heat and insensitive to pH. They still retained strong antifungal activity after treatment at pH values ranging from 2 to 12 for 24 h or at 100°C for 30 min. Therefore, it is a candidate biocontrol agent for rice bakanae controlling. Biologically active fractions were isolated by high-performance liquid chromatography (HPLC). A component of a molecular weight of 1057 Da was identified as iturin A after electrospray ionization quadrupole time of flight tandem mass spectrometry analysis (ESI-Q-TOF-MS/MS).

Design, synthesis and antibacterial activity of a novel hybrid antimicrobial peptide LFM23

Antimicrobial peptides produced by many tissues and cell types of invertebrates, insects and humans as part of their innate immune system, have received increasing attention as potential candidates due to their administration as pharmaceutical agents. In the present study, a novel hybrid antimicrobial peptide LFM23 consisting of 23 amino acid residues was designed based on the primary sequences of bovine lactoferricin (LfcinB) and melittin. The peptide was synthesized by chemical method of solidphase synthesis with a purity of more than 98% after reverse phase high performance liquid chromatography. Antimicrobial activity assay showed that LFM23 had strong antibacterial abilities, and the minimum inhibitory concentrations against Escherichia coli AT CC25922, Salmonella typhimurium ATCC12291, Pseudomonas aeruginosa ATCC27853, Staphylococcus aureus ATCC25923, Pichia pastoris GS115, were 32, 32, 64, 32 and 256 μg/ml, respectively. The hemolytic assays indicated that LFM23 had no hemolytic action in vitro at antimicrobial concentration. The results demonstrate that the peptide LFM23 has a good application prospect as clinically useful antimicrobial agents.