  The opportunistic fungal pathogen Candida albicans causes serious hematogenic
hospital acquired candidiasis with worldwide impact on public health. Because
of its importance as a nosocomial etiologic agent, C. albicans genome has been
largely studied to identify intraspecific variation and several typing methods
have been developed to distinguish closely related strains. Mitochondrial DNA
can be useful for this purpose because, as compared to nuclear DNA, its higher
mutational load and evolutionary rate readily reveals microvariants.
Accordingly, we sequenced and assembled, with 8 fold coverage, the
mitochondrial genomes of two C. albicans clinical isolates (L296 and L757) and
compared these sequences with the genome sequence of reference strain SC5314.
The genome alignment of 33,928 positions revealed 372 polymorphic sites being
230 in coding and 142 in non-coding regions. Three intergenic regions located
between genes tRNAGly/COX1, NAD3/COB and ssurRNA/NAD4L, named IG1, IG2 and IG3
respectively, which showed high number of neutral substitutions, were amplified
and sequenced from 18 clinical isolates from different locations in Latin
America and 2 ATCC standard C. albicans strains. High variability of sequence
and size were observed, ranging up to 56bp size difference and phylogenies
based on IG1, IG2 and IG3 revealed three groups. Insertions of up to 49bp were
observed exclusively in Argentinean strains relative to the other sequences
which could suggest clustering by geographical polymorphism. Because of neutral
evolution, high variability, easy isolation by PCR and full length sequencing
these mitochondrial intergenic regions can contribute with a novel perspective
in molecular studies of C. albicans isolates, complementing well established
multilocus sequence typing methods.
