Defensive symbioses are ecological partnerships built around a type of pharmaceutical exchange; a host animal is protected by antibiotics or other defensive molecules produced by symbiotic microbes. Now appreciated to be widespread in nature, defensive symbioses are largely untapped sources of novel bioactive molecules with therapeutic potential for human use and are ideal systems to understand antibiotic use in nature. Toward these aims of antibiotic discovery and contextualizing ecological antibiotic use, we have characterized the molecular defenses from symbiotic bacteria associated with North American Trachymyrmex fungus-growing ants. Across four ant species, we recovered Actinobacteria with antibacterial and antifungal activity against ecologically-relevant pathogens. Activity-guided fractionation revealed two active antibiotics. One is a putatively-novel antibiotic produced by symbiotic bacteria recovered from multiple colonies of the desert-inhabiting New Mexican ant Trachymyrmex smithi. A different molecule, the thiopeptide antibiotic GE37468, is deployed by bacteria from Trachymyrmex septentrionalis ants on Long Island, New York at the far northern limit of their range. Intriguingly, this molecule closely resembles thiopeptide antibiotics produced by other animal symbionts, including members of the human microbiome. These thiopeptides may comprise a privileged class of host-compatible defensive molecules, and as such, have encouraging therapeutic potential.

Antibiotics from ants: Molecular defenses from specialized insect microbiomes

2019 Fall National Meeting

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