Antimicrobial and molluscicidal activities of Egyptian soil-derived Streptomyces rochei.

Abstract

Actinomycetes, are abundant sources of bioactive secondary metabolites with potential antibacterial and molluscicidal effects. This work aims to isolate and characterize actinomycetes strains from Egyptian soil, emphasizing the evaluating their antibacterial efficiency, optimizating their metabolite production, and assessing molluscicidal activities against Biomphalaria alexandrina (B. alexandrina), an intermediate host of Schistosoma mansoni (S. mansoni). Nineteen actinomycetes isolates were screened for antimicrobial activity against Escherichia coli (E. coli), Salmonella typhi (S. typhi), Pseudomonas aeruginosa (P. aeruginosa), Staphylococcus aureus (S. aureus), Candida albicans (C. albicans), and Penicillium marneffei (P. marneffei). Isolate No. 10, later identified as Streptomyces rochei ASN (S. rochei ) via 16 S rDNA sequencing and phylogenetic analysis, exhibited broad-spectrum antimicrobial activity and was selected for further study. Production media optimization revealed that modified nutritional agar, starch as a carbon source, sodium nitrate as a nitrogen source, and 25 °C incubation maximized antimicrobial metabolite production. Antibacterial activity increased with extended incubation time, peaking at 8 days. Dose-dependent inhibition was observed when different concentrations (20-80%) of cell-free supernatant (CFS) from S. rochei ASN were applied to test pathogens, with S. aureus, C. albicans, and P. marneffei being most susceptible. Scanning electron microscopy revealed severe cellular and structural damage in treated microbes. The CFS also demonstrated significant molluscicidal activity, with LC₅₀ and LC₉₀ values of 26.85 ppm and 40.95 ppm, respectively. It inhibited the hatchability of B. alexandrina eggs in a concentration- and age-dependent manner, and exerted rapid, dose-dependent mortality against S. mansoni miracidia and cercariae. Histological examinations of exposed snails showed degeneration in both hermaphrodite and digestive glands, including disrupted acinar structures, damaged oocytes and spermatocytes, vacuolated digestive cells, and degenerated secretory cells. S. rochei ASN, isolated from Egyptian soil, exhibits potent antimicrobial and molluscicidal activities. Its bioactivity is significantly influenced by growth conditions and medium composition. The strain holds promise as a natural biocontrol agent against pathogenic microbes and snail vectors involved in schistosomiasis transmission, warranting further pharmacological and ecological investigations.