Broad Escovopsis‐inhibition activity of Pseudonocardia associated with Trachymyrmex ants

Abstract

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. Using Pseudonocardia strains isolated from Trachymyrmex ants, we tested whether the inhibitory capabilities of such strains are restricted to Escovopsis parasites that infect gardens of this ant genus. Twelve Pseudonocardia strains were tested in in vitro bioassays against Escovopsis strains derived from fungus gardens of Trachymyrmex (n = 1) and leaf-cutting ants (n = 3). Overall, significant differences were observed in the mycelial growth among each Escovopsis strain in the presence of Pseudonocardia. Particularly, Escovopsis from Acromyrmex and Trachymyrmex were the most inhibited strains in comparison to Escovopsis isolated from Atta. This result suggests that Pseudonocardia isolated from Trachymyrmex possibly secrete antimicrobial compounds effective against diverse Escovopsis strains. The fact that Trachymyrmex ants harbour Pseudonocardia strains with broad spectrum of activity and its defensive role on attine gardens are discussed.

Bacterial microbiomes from vertically transmitted fungal inocula of the leaf‐cutting ant Atta texana

“…These observations suggest that Pseudonocardia symbionts do not seem to play a prominent role in A. texana (at least in foundress queens or incipient nests). Whereas Pseudonocardia occur in high abundances in the integumental accretions of Trachymyrmex and Acromyrmex workers and queens (Currie et al ., ; Fernández‐Marín et al ., ; Andersen et al ., ; Meirelles et al ., ), the diversity and abundance of Pseudonocardia types associated with A. texana in our study seem to resemble the kind of diversity found in environmental sources, as for example soil.…”

“…S3). Pseudonocardia can reside in accretions on the integument of many genera of fungus‐growing ants (Currie et al ., ; Fernández‐Marín et al ., ), particularly in the genera Acromyrmex (sister clade to Atta ) and Trachymyrmex (Currie et al ., ; Fernández‐Marín et al ., ; Meirelles et al ., ). Such integumental accretions are not visible in Atta species, and previous studies indicated that integumental Pseudonocardia were absent or rare in Atta species (Currie et al ., ; Fernández‐Marín et al ., ).…”

The molecular phylogenetics ofTrachymyrmexForel ants and their fungal cultivars provide insights into the origin and coevolutionary history of ‘higher‐attine’ ant agriculture

“…However, Meirelles et al . () found several novel strains of Pseudonocardia isolated from previously unidentified Trachymyrmex s.l. species, several of which can now be identified as M. atlanticus .…”

“…Likewise, few studies to date have included actinobacteria, which grow in cuticular crypts on the ants' integuments (Currie et al, 1999b;Currie, 2001;Currie et al, 2003c;Currie et al, 2006;Cafaro et al, 2011), isolated from Mycetomoellerius species. However, Meirelles et al (2014) found several novel strains of Pseudonocardia isolated from previously unidentified Trachymyrmex s.l. species, several of which can now be identified as M. atlanticus.…”

“…The specialized fungal parasites in the genus Escovopsis Muchovej and Della Lucia (Ascomycota: Hypocreales), which are found only in association with attine nests and which compete with the ants to feed on the fungal cultivars, are only partially known for species in these genera. To date, studies have focused on Escovopsis species associated with four Mycetomoellerius species [M. zeteki (Weber), M. ruthae (Weber), M. dichrous (Kempf), M. atlanticus (Mayhé-Nunes and Brandão)] and one Paratrachymyrmex species (P. diversus) (Currie et al, 1999a;Currie et al, 2003a;Meirelles et al, 2014Meirelles et al, , 2015Birnbaum & Gerardo, 2016).…”