Leaf-cutting ants: an unexpected microenvironment holding human opportunistic black fungi

Abstract

Fungus-growing ants of the genus Atta are known for their leaf-cutting habit, a lifestyle they have maintained since their 50-million-year-old co-evolution with a mutualistic fungus, cultivated as food. Recent studies have highlighted that, in addition to the mutualistic fungus, nests of ants harbor a great diversity of microbial communities. Such microorganisms include the dematiaceous fungi, which are characterized by their melanized cell walls. In order to contribute to the knowledge of fungal ecology, as well as opportunistic strains that may be dispersed by these social insects, we isolated and identified fungi carried by gynes of Atta capiguara and Atta laevigata, collected from colonies located in Fazenda Santana, Botucatu (São Paulo, Brazil). The isolation was carried out using the oil flotation technique, which is suitable for the growth of black fungi. Inoculated plates were incubated at 25 and 35 °C until black cultures were visible (20-45 days). Isolates were identified based on microscopic and molecular characteristics. Some isolated genera were: Cladophialophora, Cladosporium, Exophiala, Ochroconis, Phaeococcomyces, Phialophora and Penidiella. Hyaline species were also found. The results obtained from this work showed that leaf-cutting gynes may contribute to the dispersal of opportunistic dematiaceous fungi. It is suggested that more attention should be paid to this still unexplored subject.

Prevalence of the genus Cladosporium on the integument of leaf-cutting ants characterized by 454 pyrosequencing

“…As gynes are at least twice the size than drones (Online Resource 2), and for this reason they have a higher contact surface with surrounding environment, we expected a higher number of reads obtained from these insects; however, we observed that A. capiguara gynes had the lowest number of reads (n = 934) and MOTUs (n = 25). Using a culturedependent technique that favored the growth of melanised fungi, Duarte et al (2014) isolated 17 fungal taxa from 100 A. capiguara gynes' integuments, a lower fungal richness compared to the present study. Fisher's alpha diversity index showed that drones of A. capiguara and A. laevigata had the highest fungal richness.…”

“…Studies on the mycobiota present on the integument of leaf-cutting ants are relatively recent and only four studies are published on this subject (Pagnocca et al 2008;Guedes et al 2012;Arcuri et al 2014;Duarte et al 2014). The relationship of these cuticular fungi with ants is still unknown but Attili-Angelis et al (2014) suggested that the presence of melanised fungi (order Chaetothyriales) may be favored by the hydrocarbon composition in the cuticle of these insects.…”

“…The study of Pagnocca et al (2008) was the first to analyse the fungal community present in the integument of leaf-cutting gynes from Atta capiguara and Atta laevigata nests and isolated several fungal species with prevalence of the genus Cladosporium. A few years later, Duarte et al (2014) reported the presence of potentially pathogenic black fungi, such as Exophiala and Ochroconis, in the gynes' body of the same species. Therefore, the fungi present in the integument of alate ants may be dispersed in the environment and thus compose the fungal community of the newly founded colony.…”

A phylogenetic perspective on the association between ants (Hymenoptera: Formicidae) and black yeasts (Ascomycota: Chaetothyriales)

“…Ant-associated Chaetothyriales can be classified into three main functional groups: (i) strains associated with fungus-growing attine ants [10][11][12]; (ii) strains involved in 'carton' structures built by ants [7,[13][14][15]; and (iii) strains associated with ant-plant symbioses [7,16]. The first group, Chaetothyriales associated with attine ants, are not the focus of our study.…”

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

“…Least understood are the microbes present in the fungal inocula (pellets) used by foundress queens as starter cultures during nest founding. A few studies used culture-dependent methods to characterize fungi present in pellets Duarte et al, 2014;Moreira et al, 2015), but the bacterial microbiomes transferred in pellets from mother to offspring nests remain completely unknown. Such vertically transmitted pellet microbiomes could play important roles for garden health and colony survival of incipient leafcutter colonies.…”