Preliminary screening of selected soils in Ilorin, North-central Nigeria for antibiotic-producing actinomycetes

The present research aimed at screening various soils within Ilorin metropolis for antibiotic producing actinomycetes. The objectives of the study were to determine physiochemical parameters of soils, the occurrence of actinomycetes in soils, antibacterial potentials and identity of isolates. Soil parameters such as pH, temperature, moisture, organic matter and soil type were evaluated following standard procedures. Selective isolation to determine the occurrence of actinomycetes was performed by soil dilution using pour plate technique on starch casein agar. Preliminary antibacterial screening against 10 clinical test bacteria was performed using cross streak method. All isolates were initially identified based on morphological and biochemical characteristics, while the most bioactive isolates were further identified by molecular means. The soils were alkaline, with temperatures between 29 °C and 31 °C, moisture was in range of 0.72 ± 0.07c and 6.62 ± 0.42b. Highest organic matter content was 32.13 ± 0.20a with soil types mostly loamy and sandy loam. Ten actinomycetes (SM1 - SM10) were isolated, with the most frequently occurring isolate being SM3 and SM5 (16.7%). SM5 was the most active, inhibiting 9 out of 10 tests, with the highest inhibition against Staphylococcus aureus 25923 (24 mm ± 0.15a). All isolates were identified as Streptomyces by morphology and biochemical tests. Based on nucleotide similarity searches and phylogeny, two bioactive Streptomycetes were suggested as novel strains and thus named as Streptomyces bottropensis UIL RNA (SM5) and S. flavoviridis UIL RNA(SM7), which may serve as promising sources of antibiotics. Actinomycetes from Ilorin metropolis demonstrated broad spectrum of antibacterial activity against clinical test bacteria.