Lack of Consistent Short Sequence Repeat Polymorphisms in Genetically Homologous Colonizing and Invasive Candida albicans Strains

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Abstract
Short sequence repeats (SSRs), potentially representing variable numbers of tandem repeat (VNTR) loci, were identified for the human-pathogenic yeast species Candida albicans by computerized DNA sequence scanning. The individual SSR regions were investigated in different clinical isolates of C. albicans. Most of the C. albicans SSRs were identified as genuine VNTRs. They appeared to be present in multiple allelic variants and were demonstrated to be diverse in length among nonrelated strains. As such, these loci provide adequate targets for the molecular typing of C. albicans strains. VNTRs encountered in other microbial species sometimes participate in regulation of gene expression and function as molecular switches at the transcriptional or translational level. Interestingly, the VNTRs identified here often encode polyglutamine stretches and are frequently located within genes potentially involved in the regulation of transcription. DNA sequencing of these VNTRs demonstrated that the length variability was restricted to the CAA/CAG repeats encoding the polyglutamine stretches. For these reasons, paired C. albicans isolates of similar genotype, either found as noninvasive colonizers or encountered in an invasive state in the same individual, were studied with respect to potentially invasion-related alterations in the VNTR profiles. However, none of the VNTRs analyzed thus far varied systematically with the transition from colonization to invasion. In contrast to the situation described for some prokaryotic species, this finding suggests that VNTRs of C. albicans may not simply function as contingency loci related to straightforward on/off regulation of invasion-related gene expression.