Yeasts isolated from a fungus-growing ant nest, including the description of Trichosporon chiarellii sp. nov., an anamorphic basidiomycetous yeast Fernando C. Pagnocca, 1 Mara F. C. Legaspe, 1 Andre Rodrigues, 1 Carla C. C. Ruivo, 1 Nilson S. Nagamoto, 2 Maurı ´cio Bacci, Jr 1 and Luiz C. Forti 2 Correspondence Fernando C. Pagnocca pagnocca@rc.unesp.br 1 Center for the Study of Social Insects, UNESP – Sa ˜ o Paulo State University, 13506-900, Rio Claro, SP, Brazil 2 Department of Vegetal Production, UNESP – Sa ˜ o Paulo State University, 18603-970, Botucatu, SP, Brazil Thirty-nine yeast strains were recovered from a field nest of a primitive and putative novel attine ant species in the genus Myrmicocrypta (Hymenoptera: Formicidae: tribe Attini). Yeasts isolated from the fungus garden and waste deposit included Candida dubliniensis, Candida oleophila, Cryptococcus haglerorum and Hanseniaspora uvarum. In addition, one morphological type was isolated overwhelmingly. Sequencing data of partial large-subunit (LSU) rDNA and the internal transcribed spacer (ITS) region coupled with morphological and physiological characterization accommodated this morphotype in a separate taxonomic position in relation to the known species of Trichosporon (Basidiomycota: Trichosporonales). Here, we propose a novel yeast species named Trichosporon chiarellii sp. nov. based on the description of 34 isolates; the type strain is strain FCP 540806 T (5CBS 11177 T ). Fungus-growing ants (Hymenoptera: Formicidae, tribe Attini) are social insects that maintain an obligate mutualism with basidiomycetous fungi (mostly in the Lepiotaceae), which they cultivate as food (Mueller et al., 1998). After 50 million years of co-evolution, the two partners have developed a successful integration, leading to 13 genera and more than 230 described ant species, all exclusive to the New World (Schultz & Brady, 2008). The fungus provides its host with suitable nutrients such as amino acids, simple sugars and enzymes (Silva et al. , 2006). In turn, the fungus is manured by the ants, and the ants promote its dispersion when reproductives found a new colony (Weber, 1972). Based on molecular and morphological evidence, attine ants are usually classified in two phylogenetic groups: the lower and higher attines (Schultz & Meier, 1995; Schultz & Brady, 2008). Nests of lower attine genera are frequently cryptic and small (usually fewer than 100 workers) and workers do not attack plants (Mueller et al., 2001). These genera include Cyphomyrmex, Mycetophylax, Mycocepurus, Myrmicocrypta, Apterostigma, Mycetagroicus, Mycetosoritis and Mycetarotes. The genera Sericomyrmex, Trachymyrmex, Acromyrmex and Atta make up the higher attines, which usually form larger nests; the number of workers may reach millions in Atta species. The latter two genera may be serious pests of agricultural crops as a result of the large numbers of leaves that these insects cut and use as substrate for their fungus (Ho ¨lldobler & Wilson, 1990). The fungus garden of attine ants is considered a microbial consortium because several microbes can be found in this particular environment in addition to the symbiotic fungus (Currie et al., 1999; Mueller et al., 2005; Rodrigues et al., 2008). For example, several authors have reported the presence of yeasts associated with field and laboratory nests of higher attines (Craven et al., 1970; Carreiro et al., 1997; Pagnocca et al., 1996, 2008). In the course of these studies, two novel yeast species, Cryptococcus haglerorum (Middelhoven et al., 2003) and Sympodiomyces attinorum (Carreiro et al., 2004), were described in association with Atta sexdens rubropilosa nests. Recently, black yeasts closely related to the genus Phialophora were reported from the bodies of attine ants as a new symbiont (Little & Currie, 2007). Considering that no studies on yeast diversity have been conducted on the lower attines to date, the aim of the present work was to profile yeasts associated with a Abbreviation: MSP-PCR, microsatellite-primed PCR. The GenBank/EMBL/DDBJ accession numbers for the 26S rDNA D1/ D2 domain and ITS1–5.8S rDNA–ITS2 sequences of strain FCP 540806 T are EU030272 and GQ338074, respectively. Mycobank accession no. MB514465. Neighbour-joining trees based on ITS1–5.8S rDNA–ITS2 region sequences and this sequence concatenated with that of the LSU rDNA D1/D2 domain are available as supplementary material with the online version of this paper. International Journal of Systematic and Evolutionary Microbiology (2010), 60, 1454–1459 DOI 10.1099/ijs.0.015727-0 1454 015727 G 2010 IUMS Printed in Great Britain