Cryptococcus gattii virulence composite: candidate genes revealed by microarray analysis of high and less virulent Vancouver island outbreak strains.
Human and animal cryptococcosis due to an unusual molecular type of Cryptococcus gattii (VGII) emerged recently on Vancouver Island, Canada. Unlike C. neoformans, C. gattii causes disease mainly in immunocompetent hosts, despite producing a similar suite of virulence determinants. To investigate a potential relationship between the regulation of expression of a virulence gene composite and virulence, we took advantage of two subtypes of VGII (a and b), one highly virulent (R265) and one less virulent (R272), that were identified from the Vancouver outbreak. By expression microarray analysis, 202 genes showed at least a 2-fold difference in expression with 108 being up- and 94 being down-regulated in strain R265 compared with strain R272. Specifically, expression levels of genes encoding putative virulence factors (e.g. LAC1, LAC2, CAS3 and MPK1) and genes encoding proteins involved in cell wall assembly, carbohydrate and lipid metabolism were increased in strain R265, whereas genes involved in the regulation of mitosis and ergosterol biosynthesis were suppressed. In vitro phenotypic studies and transcription analysis confirmed the microarray results. Gene disruption of LAC1 and MPK1 revealed defects in melanin synthesis and cell wall integrity, respectively, where CAS3 was not essential for capsule production. Moreover, MPK1 also controls melanin and capsule production and causes a severe attenuation of the virulence in a murine inhalational model. Overall, this study provides the basis for further genetic studies to characterize the differences in the virulence composite of strains with minor evolutionary divergences in gene expression in the primary pathogen C. gattii, that have led to a major invasive fungal infection outbreak.
Molecular Mycology Research Laboratory, Centre for Infectious Diseases and Microbiology, Sydney Medical School-Westmead, Westmead Millennium Institute, Sydney Emerging Infections and Biosecurity Institute, The University of Sydney, Westmead Hospital, Westmead, New South Wales, Australia.
Popchai
P
Ngamskulrungroj
Jennifer
J
Price
Tania
T
Sorrell
John R
JR
Perfect
Wieland
W
Meyer
D002170:Canada; D003453:Cryptococcosis / Q000453:epidemiology*; D056285:Cryptococcus gattii / Q000235:genetics / Q000472:pathogenicity*; D004196:Disease Outbreaks; D019143:Evolution, Molecular; D020869:Gene Expression Profiling / Q000379:methods; D015966:Gene Expression Regulation, Fungal; D005843:Geography; D006801:Humans; D020411:Oligonucleotide Array Sequence Analysis; D013045:Species Specificity; D014774:Virulence
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