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Pseudonocardia Symbionts of Fungus-Growing Ants and the Evolution of Defensive Secondary Metabolism - PubMed

  • ️Wed Jan 01 2020

Review

Pseudonocardia Symbionts of Fungus-Growing Ants and the Evolution of Defensive Secondary Metabolism

Sarah L Goldstein et al. Front Microbiol. 2020.

Abstract

Actinobacteria belonging to the genus Pseudonocardia have evolved a close relationship with multiple species of fungus-growing ants, where these bacteria produce diverse secondary metabolites that protect the ants and their fungal mutualists from disease. Recent research has charted the phylogenetic diversity of this symbiosis, revealing multiple instances where the ants and Pseudonocardia have formed stable relationships in which these bacteria are housed on specific regions of the ant's cuticle. Parallel chemical and genomic analyses have also revealed that symbiotic Pseudonocardia produce diverse secondary metabolites with antifungal and antibacterial bioactivities, and highlighted the importance of plasmid recombination and horizontal gene transfer for maintaining these symbiotic traits. Here, we propose a multi-level model for the evolution of Pseudonocardia and their secondary metabolites that includes symbiont transmission within and between ant colonies, and the potentially independent movement and diversification of their secondary metabolite biosynthetic genes. Because of their well-studied ecology and experimental tractability, Pseudonocardia symbionts of fungus-growing ants are an especially useful model system to understand the evolution of secondary metabolites, and also comprise a significant source of novel antibiotic and antifungal agents.

Keywords: Pseudonocardia; attine ant mutualism; evolution; specialized (secondary) metabolite; symbiosis.

Copyright © 2020 Goldstein and Klassen.

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Conflict of interest statement

The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.

Figures

FIGURE 1
FIGURE 1

(A) Ventral view of an adult Trachymyrmex septentrionalis worker ant, showing the localization of Pseudonocardia (white patches) on the laterocervical plates that is typical of adult worker ants. (B) Enlargement of the laterocervical plates from (A). Photo credit: Mark Smith, Macroscopic Solutions; used with permission.

FIGURE 2
FIGURE 2

Ecological and evolutionary mechanisms that may govern the diversity of Pseudonocardia fungus-growing ant symbionts. Scenarios (A–C) all describe transmission involving other Pseudonocardia symbionts, either vertically within an established ant colony (A), horizontally between established colonies (B), or during colony founding (C). Scenario (D) describes the acquisition of new symbionts from the external environment, and scenario (E) describes the horizontal transfer of genes from those environmental microbes without acquisition of the microbes themselves. Note that the experimental evidence supporting each scenario varies. Figure created with

BioRender.com

.

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