A naturally isolated co-culture of Streptomyces species displays antifungal synergy

Fungal pathogens pose unique threats to modern healthcare: clinical treatment is currently limited to four antifungal drug classes and many drugs produce adverse side effects in patients. Exploration of new environments could lead to the isolation of novel antifungal-producing microorganisms.

Here, we report the isolation and characterization of a mixed isolate of two Streptomyces species from dried moth larvae (Cirina forda) that exhibited synergistic antifungal activity.

Diluted samples were plated on Gauze agar. Colonies were picked based on morphology and cell structure. Mature colonies were cultivated on MYM and overlayed with soft agar containing a bacterial or fungal species. Whole genome sequencing (WGS) was performed for phylogenetic identification and characterization. Activity of the colonies and cell extracts was further characterized by a panel of whole-cell biosensors, which contain the luciferase cassette under the control of an antibiotic-inducible promotor. Potential biosynthetic gene clusters were identified by genome mining.

The isolated actinobacterium displayed antibacterial and antifungal activity. Variation in colony morphology led to the subculturing of two morphologically different isolates; these experienced a decrease in antifungal activity. Both sub-strains were identified by WGS as Streptomyces albidoflavus. Multiple genomic variations found between the strains by comparative analysis could be responsible for differences in strain physiology. Biosensor tests indicated potential production of antifungal polyene macrolide-like molecules in all three isolates. Further characterization of the synergistic antifungal activity between the co-isolated strains is currently ongoing.

We were able to demonstrate the co-isolation of antifungal-producing organisms from a niche habitat displaying a naturally synergistic relationship. Further research towards these associations could aid the discovery and development of new and better tolerated antifungals.