title: Isolation, Partial Puriﬁcation and Characterization of an Antimicrobial Compound, Produced by Bacillus atrophaeus.
abstract: BACKGROUND
  Antibiotics are usually assumed as secondary metabolites produced during the idiophase of microbial growth, which can kill or inhibit the growth of other microorganisms. Nowadays, indiscriminate use of antibiotics has resulted in resistant microorganisms. Therefore, screening researches on products with antimicrobial activities are necessary.
  
  
  OBJECTIVE
  To find new antibiotics to defend against pathogenic microorganisms resistant to common antibiotics, the bacterium isolated from skin of the frog called Rana ridibunda was studied for its antimicrobial activities.
  
  
  METHODS
  An antibiotic-producing bacterium was isolated from the frog skin. The bacterium was identified based on 16SrDNA sequencing and biochemical and morphological characteristics. Antimicrobial activity of the culture supernatant was examined against laboratorial standard bacteria by disc diffusion and minimum inhibitory concentration (MIC) methods. To characterize the produced antimicrobial compound, the culture supernatant of the bacterium was washed by chloroform and dried at 40°C; then, the antimicrobial substance was extracted by methanol and acetone and detected by bioautography on silica gel plates. Dialysis tube was used to find the molecular weight of this substance.
  
  
  RESULTS
  The isolated bacterium was identified as a new strain of Bacillus atrophaeus. The antimicrobial substance exhibited heat stability between 25ºC and 100ºC and was active in a broad pH range from 2.0 to 11.0. The bioautography assay showed that methanol was the optimum solvent for the extraction of antimicrobial substance. The dialysis tube indicated that the antimicrobial substance weight was less than 1 kDa and the compound did not precipitate with ammonium sulfate.
  
  
  CONCLUSIONS
  This study showed that some properties of antimicrobial substances produced by the GA strain differed from other peptide antibiotics produced by the genus Bacillus such as bacitracin, which increases the likelihood of its novelty.
authors.affiliation: Department of Microbiology, Faculty of Biological Sciences, Shahid Beheshti University, Tehran, IR Iran.
authors.forename: Gholam Hossein
authors.initials: GH
authors.lastname: Ebrahimipour
authors.affiliation: Department of Microbiology, Faculty of Biological Sciences, Shahid Beheshti University, Tehran, IR Iran.
authors.forename: Zahra
authors.initials: Z
authors.lastname: Khosravibabadi
authors.affiliation: Department of Microbiology, Faculty of Biological Sciences, Shahid Beheshti University, Tehran, IR Iran.
authors.forename: Hossein
authors.initials: H
authors.lastname: Sadeghi
authors.affiliation: Department of Microbiology, Research Institute of Medical Plants and Drug, Shahid Beheshti University, Tehran, IR Iran.
authors.forename: Atusa
authors.initials: A
authors.lastname: Aliahmadi
keywords: Antimicrobial Agent; Bacillus; Frog