Production of antibacterial and antioxidant agents by Actinobacteria using soybean meal as a nitrogen source

Abstract

Actinobacteria are mainly found in soil and some of them have properties that are common to bacteria and fungi, despite having quite distinct characteristics. Unlike bacterial colonies in general, which are clearly slimy and grow rapidly, some groups of actinobacteria colonies grow slowly by showing a powdery consistency and are tightly attached to the agar surface. Observations on a colony under the microscope showed that many of them form asexual spores for their reproduction. Many metabolite compounds generated by actinobacteria have promising activities like antioxidant and antagonistic activity against bacteria and fungi. The production of these compounds depends not only on the strain of the organism but also on the medium in which it is grown and the growth conditions. Moreover, agricultural by-products such as soybean meal are known to have high protein content, thus it can be potentially used as an alternative media for actinobacteria. In this research, ten actinobacterial strains were isolated from the soil. After seven days of cultivation with the medium containing soybean meal, the cultures were subjected to ethyl acetate extraction. Five extracts exhibited antibacterial properties against Bacillus subtilis with a zone of inhibition ranging from 10–14 mm. One extract could strongly inhibit Staphylococcus aureus with an inhibition zone of 21 mm. However, none of them were active against Escherichia coli. Five extracts demonstrated antioxidant DPPH radical scavenging activity with more than 40%.