ANTIMICROBIAL ACTIVITIES OF STREPTOMYCES SPECIES ISOLATED FROM SOIL SAMPLES OBTAINED FROM FRUIT WASTE DUMP SITE AT SHASHA MARKET, AKURE, NIGERIA

Abstract

This research examined the antimicrobial activities of Streptomyces species isolated from soils of fruit waste dump site at Shasha Market, Akure, Ondo State. Soil samples were collected from four different fruit waste dump sites which are banana, carrot, tomato and orange dump sites from the location mentioned above with the aid of soil auger from the depth of 15 cm and Streptomyces were isolated using soil dilution technique and starch casein agar. The Streptomyces isolates were assessed for antimicrobial activity by the cross-streak technique. Production of antimicrobial metabolite was carried out in a fermentation medium. Optimization for antimicrobial metabolite production was carried out. Extraction of antimicrobial metabolite was carried out using ethyl acetate as solvent and purification of the crude extract was carried out using column and thin layer chromatography to determine the retention factor of the purified fractions. The purified extract was characterized using Fourier Transform Infrared (FTIR) analysis. Susceptibility of the test bacteria to antibiotics was carried out. The antimicrobial activities of the crude and purified extracts of the Streptomyces species was evaluated by agar well diffusion assay on plant and human bacteria and fungi. Ten Streptomyces species were isolated from fruit waste dump sites. Streptomyces rimosus TOMT and Streptomyces antibioticus TOMT were isolated from tomato dump site. Streptomyces citreus ORNG, Streptomyces albus ORNG, Streptomyces famosus ORNG, Streptomyces viridoflavus ORNG, Streptomyces flavovirens ORNG and Streptomyces rochei ORNG were isolated from orange dump site. Also, Streptomyces spiralis CART and Streptomyces griseoflavus BANA were isolated from carrot and banana dump sites respectively. In the preliminary screening of the antimicrobial activities of the Streptomyces species, five out of the ten isolates possessed antimicrobial activities against the test organisms. They were Streptomyces albus ORNG, Streptomyces viridoflavus ORNG, Streptomyces spiralis CART, Streptomyces flavovirens ORNG and Streptomyces rochei ORNG. Out of the five isolates, three were Streptomyces albus ORNG, Streptomyces flavovirens ORNG and Streptomyces rochei ORNG. Optimum production of antimicrobial metabolite by Streptomyces albus ORNG, Streptomyces flavovirens ORNG and Streptomyces rochei ORNG occurred at pH of 8. Culture medium amended with glucose served as good carbon source for maximum production of antimicrobial metabolites. Effect of ultraviolet radiation on the Streptomyces isolates resulted to decrease in inhibition zones against the plant and human bacteria and fungi. The crude extract showed antimicrobial activity against all the test bacteria and fungi. The purified extracts of Streptomyces albus ORNG, Streptomyces flavovirens ORNG and Streptomyces rochei ORNG gave retention factors of 0.47 cm, 0.58 cm and 0.55 cm respectively. The maximum antibacterial activity of Streptomyces albus ORNG was observed against Streptococcus spp. The maximum antifungal effect of Streptomyces flavovirens ORNG was observed against Sclerotium russia, while maximum antifungal activity of Streptomyces rochei ORNG was observed on Aspergillus fumigatus. Ciprofloxacin was the most active antibiotic with broad spectrum of activity. Nystatin showed maximum activity against Candida albicans. Mancozeb showed maximum activity against Colletotrichum spp. The minimum inhibitory concentration of the purified extracts ranged between 3.1 mg/ml and 50 mg/ml. The infrared analysis revealed the possibility of the presence of phenolic compounds in the purified extract. The antimicrobial metabolites obtained from Streptomyces species in this study showed significant inhibition on the selected bacteria and fungi. This emphasizes the role of soil Streptomyces in modern drug discovery, production of novel antimicrobial compounds to target resistant bacteria and biocontrol of plant pathogens.