YAZI ABDULLAH JASSIM*, MARWA KADHIM KHUDHAIR AND SAFA HASAN RADHI
Department of Biology, College of Science, Babylon University, Babylon, Iraq
*(e-mail : yaziabdalla2014@gmail.com; Mobile : 078097 42785)
(Received : December 10, 2021, Accepted : February 13, 2022)
ABSTRACT
Twenty-five soil samples were collected from five different sites. Three isolates were identified for their
antibacterial activity against pathogenic bacteria through primary screening protocol and on their inhibitory
activity against the pathogenic bacteria. These were tested for their antibacterial activity through secondary
screening protocol. These isolates were identified and diagnosed using many physiological, biochemical
tests and amplification of 16S rRNA gene sequence. The isolates were identified as Bacillus subtilis (B1)
and two Bacillus polymyxa (B4) and (B7). These had high inhibitory activity against Escherichia coli and
Staphylococcus aureus with inhibition zone reaching to 34 mm and less activity against Klebsiella pneumonia
and Pseudomonas aeruginosa. B1 isolate was characterized by greater inhibitory activity against pathogenic
bacteria. The antibacterial agents that produced by these isolates were characterized by three different
methods. First : The ultraviolet spectroscopy (UV) for measuring the max, the results showing the
range of this assay from 234 to 350 nm. Second : Infrared spectroscopy (FT-IR) in the range from 400 to
4000/cm. Third : Liquid chromatography by mass spectrometer analysis. The effect of temperature on
the growth of the two isolates showed that they were developing well in temperature 40 and 45°. Both
isolates were unable to grow at a temperature of 5°C and the effect of salinity on the growth of the
isolates showed that they were developing well in 3% NaCl concentration. Only B1 was able to grow till
6% NaCl concentration, while both isolates were unable to grow at 10% concentration of sodium chloride.
Activity of antioxidant was determined by using DPPH (2,2-diphenyl-2-picrylhydrazyl). The extract bacterial
had the highest antioxidant activity with median effective dose (IC50) as 5.24±8.0 µg/ml.
Key words : : 16S rRNA, antioxidant activity, Bacillus, DPPH, IC50