Resumo

Attine ants maintain an association with antibiotic-producing Actinobacteria found on their integuments. Evidence supports these bacteria as auxiliary symbionts that help ants to defend the fungus gardens against pathogens. Here we tested whether the inhibitory capabilities of Pseudonocardia strains from Trachymyrmex ants are restricted to Escovopsis parasites that infect gardens of this ant genus. Twelve Pseudonocardia strains were tested against four Escovopsis strains derived from fungus gardens of Trachymyrmex (n= 1) and leaf-cutting ants, including strains isolated from Acromyrmex (n = 2) and Atta (n = 1). For comparison, we included Streptomyces and Actinoplanes bacteria isolated from the integument of Trachymyrmex ants. The Escovopsis mycelial growth was measured using ImageJ, and six replicates were made for each actinobacteria-Escovopsis combination. Two-way ANOVA was used to evaluate differences between challenges. In addition, all Pseudonocardia strains were identified by 16S rDNA sequencing. Our results revealed that all Pseudonocardia strains share identical 16S rDNA sequences and database search revealed that the GenBank closest relative only share 96% of similarity with our strains. Moreover, our results revealed significant differences in the inhibition of the mycelial growth among the four tested Escovopsis strains (p < 0.05). Most interesting, Pseudonocardia strongly inhibited Escovopsis isolated from an Acromyrmex garden in comparison to the other strains. This result suggests that Pseudonocardia isolated from Trachymyrmex possibly secrete antimicrobial compounds effective against diverse Escovopsis strains. The fact that Trachymyrmex ants harbor Pseudonocardia strains with broad spectrum of activity may be used by the ants as a strategy to defend their fungus gardens against multiple strains of the parasite.