Evaluation of the Biological Activities (Antimicrobial and Antioxidant) of Bioactive Compound-Producing Actinomycetes Isolated from the Soil of the Mkhalled Coast (Tlemcen, Western Algeria)

Abstract

Algerian coastal terrestrial ecosystems and soil include a large diversity of microorganisms that can provide a remarkable origin of biologically active substances used in multiple sectors such as pharmaceuticals, industry, biological agriculture, and medicine. In our study, we analyzed the antimicrobial and antioxidant activities of actinomycete strains isolated from the soil of forest and mountainous coastal areas of Mkhalled. Extracts from these actinomycete strains were acquired from fermentation in liquid media (Benett, AF, and GNG medium). A total of 11 strains were isolated using ISP2, GNG medium, TSA medium, Gauss and others and identified using different media (gelatin agar, casein agar, TSI, citrate test, catalase test, gram staining, etc.). Evaluating the antimicrobial activity using the cylinder agar method on 5 purified strains showed that E3.2 exhibits an inhibition zone approximately 11 mm against Bacillus cereus and 8 mm against Klebsiella pneumoniae, strains such as E1.9 and E1.11 showed remarkable activity against Pseudomonas aeruginosa, with inhibition zones of 9.75 and 9.5 mm, and no activity was on Candida albicans. Moreover, the well diffusion method indicates that all strains did not show any inhibition zone, possibly due to different reasons: insufficient active metabolites, resistance of the bacteria tests, or technical problems such as unsuitable well diameter or insufficient pre-diffusion time before incubation. Regarding the antioxidant activity achieved with the extracts obtained after fermentation, the results show that strain E1.9 presented the best total antioxidant capacity, with a maximum value of 8.5 mg AAE/g of dry extract on Bennett medium, as well as the highest activity of trapping the DPPH radical, reaching 88% inhibition. The E3.2 strain grown on AF medium also showed remarkable antioxidant activity, with a total antioxidant capacity of 6.7 mg EAA/g dry extract and an inhibition of DPPH of about 59%. This indicates that there are strains that are more potent compared to the others, which depend on nature, the composition of the media, and the cultivated strainsBesides, the diversity and differentiation of Algerian coastal soils submit a large biological potential as antimicrobial and antioxidant to be more explored and more discovered.