The Biological Activity of Protein Extracts of Bacillus spp. Isolated from Soil against Some Pathogenic Bacteria


Forty soil samples were collected from different regions in Baghdad city. Among 52 isolates, only 38 (73.1 %) belonged to Bacillus spp. All bacterial isolates were submitted to the cultural, microscopical, biochemical examination and VITEK 2 System. Bacillus cereus was the predominant (21; 55.3%) followed by Bacillus subtilis (11; 28.9%), then Bacillus amyloliquefaciens (6;15.8%). B. cereus (B1) and B. subtilis (B16) isolates showed the highest level of antibacterial activity; therefore, their extracellular proteins were extracted, purified using ammonium sulfate (80%) saturation, and submitted to Sepharose-6B gel filtration column. SDS-polyacrylamide gel electrophoresis was used to determine the molecular weights of the proteins, in which one band of molecular weight 68 and 50kDa was found in B. cereus and B. subtilis respectively. These proteins revealed high antibacterial activity on Gram positive bacteria, and moderate effect on Gram negative bacteria, except Pseudomonas aeruginosa where no effect was reported. The antibiofilm activity of the extract showed increased effect against Streptococcus pyogens, while moderate effect against each of Staphylococcus aureus, Escherichia coli, Serratia marcescens, Klebsiella spp with no impact against P.aeruginosa. The results of cytotoxicity indicated that the purified extract had a higher cytotoxic effect on the breast cancer cell line MCF7 cells at 1000µg/ml concentration, than the crude extract that showed cytotoxic effect on the same cell line at 100µg/ml.