Interactions between the pathogenic fungus Cryptococcus neoformans and ants

Despite the growing number of environmental surveys aimed to understand the ecology of the fungal pathogens Cryptococcus neoformans and Cryptococcus gattii, little is known about their relationships with arthropods. In the present study we collected a large number of samples from trees and arthropods living on them to determine the occurrence of Cryptococcus in arthropods, to understand if they could represent a vehicle for dispersion in the environment, and finally to investigate how they might interact with the fungus. Samples were collected from seven different geographical areas of the world: northwestern Italy, southeastern Italy, Slovenia, Kosovo, Greece, Turkey, and Colombia. A total of 1396 trees were examined and 11,805 samples were collected, including 7492 arthropod samples. Arthropod positive samples, mostly from ants, were found only in northwestern and southeastern Italy, Greece, and Slovenia with an average rate of 0.2%. Thirty-three of positive trees hosted positive arthropods whereas in six of them arthropods resulted negative. In addition, for six trees, positive samples from arthropods were not associated with positive arboreal samples. In vitro experiments showed that ants can transfer cryptococcal yeasts from a contaminated substrate (soil or bark) to a sterile one and that the fungus can survive inside the digestive apparatus of ants. The present study showed that ants are potential vehicles for C. neoformans although the frequency of which they enter in contact with the fungus is low. Cryptococcal yeasts can survive within the bodies of ants, but it remains unclear whether the relationship they establish with their host is parasitic, commensal, or symbiotic.