Abstracts (first author)
Specificity and stability of the Acromyrmex-Pseudonocardia symbiosis in changing environments
Fungus-growing ants live in a complex symbiosis involving both fungal and bacterial partners. Among these are Actinobacteria of the genus Pseudonocardia that are maintained on the ant cuticle to produce antibiotics, primarily against a parasitic fungus of the garden symbiont. The symbiosis has been assumed to be a hallmark of evolutionary stability, but this notion has been challenged by culturing and sequencing data. We used 454 pyrosequencing of 16S rRNA to estimate the diversity of the cuticular bacterial community of the leaf-cutting ant Acromyrmex echinatior from Panama. We used field and lab samples of the same colonies, the latter after colonies had been kept under laboratory conditions for up to 10 years. We show that the bacterial communities are highly colony-specific and stable over time. The majority of colonies (25/26) had a single dominant Pseudonocardia strain and only two strains were found in the Gamboa population across 17 years, confirming an earlier study. The microbial community on newly hatched ants consisted almost exclusively of Pseudonocardia while other Actinobacteria were identified in lower abundances on older ants. These findings are consistent with recent theory predicting that mixtures of antibiotic-producing bacteria can remain mutualistic when dominated by a single vertically transmitted strain.