Extraction and Purification of Secondary Metabolites from Bacillus spp. and Study of their Antimicrobial Activities against some Bacterial Species

(Eman A. Al-Imara, and Ghaidaa J. Al-Gazzawy)

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Abstract

Due to the increase in bacterial antibiotic resistance, there is a need to find new bioactive substance derived from non-pathogenic bacteria that is ubiquitous in environment. This study aimed to purify locally isolated Bacillus spp. secondary metabolites in addition to study their antimicrobial activities against some bacterial species. Fifty water and sediments samples were collected from different locations in Basrah Governorate, southern Iraq. Out of these isolates, twenty bacterial spore-forming isolates showed antibacterial activity against gram negative and positive bacteria. The isolates were identified biochemically by VITEK2 BCL cards, which showed that 15 isolates were Bacillus subtilis whereas the remaining five isolates were B. amyloliquefaciens. Secondary metabolites (SM) were produced and extracted from Bacillus spp. and SM extracts of BS8 and BS14 were chosen for further study. SM extracts of BS8 and BS14 were purified. The results of electrophoresis showed that the molecular weight of BS8 SM was 3779 Dalton while the molecular weight of BS14 SM was 379 Dalton; i.e. low molecular weight peptides. Statistical analysis showed significant differences (p < 0.05) in inhibitory activity among Bacillus isolates. BS8 SM extract had the best antibacterial activity (p < 0.05) among Bacillus isolates against target bacteria. K. kristinae was the most susceptible species (p < 0.05) among target bacteria while P. aeruginosa was the most resistant species (p < 0.05) among target bacteria. The results revealed the possibility of obtaining bioactive substances that can resolve many environmental problems. These substances are environmental friendly, cheap, easy to decompose, and do not leave toxic compounds. The study recommended the exploration of new antibacterial compounds originated from bacteria isolated from local environment using non-expensive extraction methods. Key Words: Antibacterial Peptides, Bacillus species, Competition effect.
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