Analysis of the bacterial communities associated with two ant-plant symbioses

Insect fungiculture is practiced by ants, termites, beetles, and gall midges and it has been suggested to be widespread among plant–ants. Some of the insects engaged in fungiculture, including attine ants and bark beetles, are known to use symbiotic antibiotic-producing actinobacteria to protect themselves and their fungal cultivars against infection. In this study, we analyze the bacterial communities on the cuticles of the plant–ant genera Allomerus and Tetraponera using deep sequencing of 16S rRNA. Allomerus ants cultivate fungus as a building material to strengthen traps for prey, while Tetraponera ants cultivate fungus as a food source. We report that Allomerus and Tetraponera microbiomes contain >75% Proteobacteria and remarkably the bacterial phyla that dominate their cuticular microbiomes are very similar despite their geographic separation (South America and Africa, respectively). Notably, antibiotic-producing actinomycete bacteria represent a tiny fraction of the cuticular microbiomes of both Allomerus and Tetraponera spp. and instead they are dominated by γ-proteobacteria Erwinia and Serratia spp. Both these phyla are known to contain antibiotic-producing species which might therefore play a protective role in these ant–plant systems.