Long-distance dispersal and recombination in environmental populations of Cryptococcus neoformans var. grubii from India

The basidiomycete yeast Cryptococcus neoformans is a cause of significant morbidity and mortality in immunocompromised hosts throughout the world. The sporadic nature of the infection and the limited empirical evidence for direct human-to-human transmission have led to the belief that infections in humans are predominantly caused by the inhalation of basidiospores from environmental sources. Therefore, analysing the structure of environmental populations of C. neoformans can significantly increase our understanding of its ecology, evolution and epidemiology. Decaying wood is a rich source of organic and inorganic compounds and is known to be a suitable ecological niche for many micro-organisms, including C. neoformans. However, relatively little is known about the population structure of C. neoformans sampled from decaying wood. In this study, we analysed samples of C. neoformans var. grubii colonizing decaying wood in tree hollows of nine tree species in five geographical locations (Delhi, Bulandshahar, Hathras, Amritsar and Amrouli) in north-western India. Multilocus sequence typing was conducted using five gene fragments for each of 78 isolates. All isolates belonged to mating type alpha. Population-genetic analyses identified no evidence for significant differentiation among populations belonging to either different geographical areas or different host tree species. Interestingly, despite the lack of mating type a strains in our survey, we found unambiguous evidence for recombination in our population analyses. Our results are consistent with the hypothesis of long-distance dispersal and recombination in environmental populations of this species in India.