Actinomycetes are prolific sources of bioactive molecules. Traditional workflows including bacterial isolation, fermentation, metabolite identification, and structure elucidation have resulted in high rates of natural product rediscovery in recent years. Recent advancements in multi-omics techniques have uncovered cryptic gene clusters within the genomes of actinomycetes, potentially introducing vast resources for the investigation of bioactive molecules. While developments in culture techniques have allowed for the fermentation of difficult-to-culture actinomycetes, high throughput metabolite screening has offered plenary tools to accelerate hits discovery. A variety of new bioactive molecules have been isolated from actinomycetes of unique environmental origins, such as endophytic and symbiotic actinomycetes. Synthetic biology and genome mining have also emerged as new frontiers for the discovery of bioactive molecules. This review covers the highlights of recent developments in actinomycete-derived natural product drug discovery.

Silver nanoparticles (Ag-NPs) have been known to possess unique antimicrobial properties which help in medicine and water treatment, but their potentials in agriculture have not been fully utilized. This study was conducted to determine the inhibitory activity of bio-synthesized Silver nanoparticles on strains of Clavibacter michiganensis subsp. Michiganensis, causative agents of canker disease of tomato plant. The Ag-NPs were synthesized using Cladosporium cladosporioides, leaf extracts of Azadirachta indica and Vernonia amygdalina. The synthesized silver nanoparticles were characterized using UV-visible absorption spectroscopy. The antibacterial activities of bio-synthesized Ag-NPs on strains of C. michiganensis subsp. michiganensis were evaluated using agar well diffusion method. UV-visible spectroscopic analysis revealed rapid reduction of silver ions by C. cladosporioides, A. indica and V. amygdalina extracts where surface Plasmon absorption maxima were observed at 400nm – 450nm from the UV-visible spectra. The in-vitro antibacterial activities revealed that Ag-NPs synthesized using V. amygdalina and A. indica extracts inhibited the growth of C. michiganensis subsp. michiganensis strains with zones of inhibition ranging from 15.70 mm - 24.70mm and 21.00mm – 30.00mm, respectively, while those synthesized using C. cladosporioides showed zones of inhibition ranging from 0.00mm – 12.00mm. Growth curves of C. michiganensis subsp. michiganensis strains in the presence of biosynthesized Ag-NPs showed inhibition of growths after 4 – 10 hours of exposure. The results of this study indicated that the bio-synthesized silver nanoparticles could be effective in controlling bacterial canker disease of tomato plant caused by strains of C. michiganensis subsp. michiganensis thereby reducing the toxic effects of chemical bactericides on important agricultural products.Keywords: Silver nanoparticles; inhibitory activity; canker, tomato; zones of inhibition