Comparative genomics using Candida albicans DNA microarrays reveals absence and divergence of virulence-associated genes in Candida dubliniensis

Abstract

Candida dubliniensis is a pathogenic yeast species closely related to Candida albicans. However, it is less frequently associated with human disease and displays reduced virulence in animal models of infection. Here comparative genomic hybridization was used in order to assess why C. dubliniensis is apparently less virulent than C. albicans. In these experiments the genomes of the two species were compared by co-hybridizing C. albicans microarrays with fluorescently labelled C. albicans and C. dubliniensis genomic DNA. C. dubliniensis genomic DNA was found to hybridize reproducibly to 95.6 % of C. albicans gene-specific sequences, indicating a significant degree of nucleotide sequence homology (> 60 %) in these sequences. The remaining 4.4 % of sequences (representing 247 genes) gave C. albicans/C. dubliniensis normalized fluorescent signal ratios that indicated significant sequence divergence (< 60 % homology) or absence in C. dubliniensis. Sequence divergence was identified in several genes (confirmed by Southern blot analysis and sequence analysis of PCR products) with putative virulence functions, including the gene encoding the hypha-specific human transglutaminase substrate Hwp1p. Poor hybridization of C. dubliniensis genomic DNA to the array sequences for the secreted aspartyl proteinase-encoding gene SAP5 also led to the finding that SAP5 was absent in C. dubliniensis and that this species possesses only one gene homologous to SAP4 and SAP6 of C. albicans. In addition, divergence and absence of sequences in several gene families was identified, including a family of HYR1-like GPI-anchored proteins, a family of genes homologous to a putative transcriptional activator (CTA2) and several ALS genes. This study has confirmed the close relatedness of C. albicans and C. dubliniensis and has identified a subset of unique C. albicans genes that may contribute to the increased prevalence and virulence of this species.

Extensive chromosome rearrangements distinguish the karyotype of the hypovirulent species Candida dubliniensis from the virulent Candida albicans

“…C. dubliniensis is more sensitive to elevated temperatures (Sullivan and Coleman 1998), it makes chlamydospores profusely under conditions where C. albicans does not make them (Staib and Morschhauser 1999), and, most importantly from the point of view of infectious disease, it is less virulent than C. albicans (Gilfillan, Sullivan et al 1998). A pioneering microarray study suggested that 247 C. albicans genes are missing or are less than 60% homologous in C. dubliniensis (Moran, Stokes et al 2004). With the achievement of the sequence of C. dubliniensis it is important to examine the chromosome structure to determine whether karyotypic differences play a role in the divergent properties.…”

“…C. dubliniensis is found mostly as an oral pathogen and only rarely in disseminated infections (Gilfillan, Sullivan et al 1998). However, it has been estimated that more than 88% of the genes of these closely related species have nucleotide homology greater than 80% (Moran, Stokes et al 2004). In addition, the two species share the ability to grow as yeast, pseudohyphae, and hyphae and to make chlamydospores.…”

Biofilm formation and adhesive/invasive properties of Candida dubliniensis in comparison with Candida albicans

“…However, comparisons of both spp. in genomes confirmed some principal differences described in the putative ortholog genes from the SAP and ALS families, known to play a significant role in adhesion [11,27]. Additionally, both genomes vary in their telomere associated genes (TLO, family of putative transcription factors) as well as in their leucine rich repeat protein genes (IFA, family of putative transmembrane proteins) that may explain the diminished pathogenicity of C. dubliniensis.…”

Differential Interaction of the Two Related Fungal SpeciesCandida albicansandCandida dubliniensiswith Human Neutrophils

“…Some of these virulence factors, found in C. albicans, however, are lacking or are reduced in C. dubliniensis (9,10,66). Aside from C. albicans, C. dubliniensis is the only Candida species that has the capacity to produce true hyphae (3), but with far less efficiency and under fewer conditions.…”

“…The phylogenetic properties of C. dubliniensis have been well described in the literature (2,8). A DNA hybridization array (9) and lately comparison of both genomes (10) uncovered particular differences between C. dubliniensis and C. albicans in regard to putative virulence genes, including those encoding hyphae-associated factors such as specific secreted proteases or invasins. The ability of C. albicans to reversibly switch between yeast and filamentous growth forms has widely been documented as an important virulence attribute of C. albicans, facilitating host invasion and colonization.…”