Cryptococcus gattii in North American Pacific Northwest: Whole-Population Genome Analysis Provides Insights into Species Evolution and Dispersal
Authors: Engelthaler David M. , Hicks Nathan D. , Gillece John D. , Roe Chandler C. , Schupp James M. , Driebe Elizabeth M. , Gilgado Felix , Carriconde Fabian , Trilles Luciana , Firacative Carolina , Ngamskulrungroj Popchai , Castañeda Elizabeth , Lazera Marcia dos Santos , Melhem Marcia S. C. , Pérez-Bercoff Åsa , Huttley Gavin , Sorrell Tania C. , Voelz Kerstin , May Robin C. , Fisher Matthew C. , Thompson George R. , Lockhart Shawn R. , Keim Paul , Meyer Wieland 
Published: July 2014

ABSTRACT

The emergence of distinct populations of
Cryptococcus gattii
in the temperate North American Pacific Northwest (PNW) was surprising, as this species was previously thought to be confined to tropical and semitropical regions. Beyond a new habitat niche, the dominant emergent population displayed increased virulence and caused primary pulmonary disease, as opposed to the predominantly neurologic disease seen previously elsewhere. Whole-genome sequencing was performed on 118
C. gattii
isolates, including the PNW subtypes and the global diversity of molecular type VGII, to better ascertain the natural source and genomic adaptations leading to the emergence of infection in the PNW. Overall, the VGII population was highly diverse, demonstrating large numbers of mutational and recombinational events; however, the three dominant subtypes from the PNW were of low diversity and were completely clonal. Although strains of VGII were found on at least five continents, all genetic subpopulations were represented or were most closely related to strains from South America. The phylogenetic data are consistent with multiple dispersal events from South America to North America and elsewhere. Numerous gene content differences were identified between the emergent clones and other VGII lineages, including genes potentially related to habitat adaptation, virulence, and pathology. Evidence was also found for possible gene introgression from
Cryptococcus neoformans
var.
grubii
that is rarely seen in global
C. gattii
but that was present in all PNW populations. These findings provide greater understanding of
C. gattii
evolution in North America and support extensive evolution in, and dispersal from, South America.

IMPORTANCE
Cryptococcus gattii
emerged in the temperate North American Pacific Northwest (PNW) in the late 1990s. Beyond a new environmental niche, these emergent populations displayed increased virulence and resulted in a different pattern of clinical disease. In particular, severe pulmonary infections predominated in contrast to presentation with neurologic disease as seen previously elsewhere. We employed population-level whole-genome sequencing and analysis to explore the genetic relationships and gene content of the PNW
C. gattii
populations. We provide evidence that the PNW strains originated from South America and identified numerous genes potentially related to habitat adaptation, virulence expression, and clinical presentation. Characterization of these genetic features may lead to improved diagnostics and therapies for such fungal infections. The data indicate that there were multiple recent introductions of
C. gattii
into the PNW. Public health vigilance is warranted for emergence in regions where
C. gattii
is not thought to be endemic.