Candida orthopsilosis and Candida metapsilosis spp. nov. to replace Candida parapsilosis groups II and III

Abstract

Two new species, Candida orthopsilosis and C. metapsilosis, are proposed to replace the existing designations of C. parapsilosis groups II and III, respectively. The species C. parapsilosis is retained for group I isolates. Attempts to construct a multilocus sequence typing scheme to differentiate individual strains of C. parapsilosis instead revealed fixed DNA sequence differences between pairs of subgroups in four genes: COX3, L1A1, SADH, and SYA1. PCR amplicons for sequencing were obtained for these four plus a further seven genes from 21 group I isolates. For nine group II isolates, PCR products were obtained from only 5 of the 11 genes, and for two group III isolates PCR products were obtained from a different set of 5 genes. Three of the PCR products from group II and III isolates differed in size from the group I products. Cluster analysis of sequence polymorphisms from COX3, SADH, and SYA1, which were common to the three groups, consistently separated the isolates into three distinct sets. All of these differences, together with DNA sequence similarities <90% in the ITS1 sequence, suggest the subgroups should be afforded species status. The near absence of DNA sequence variability among isolates of C. parapsilosis and relatively high levels of sequence variability among isolates of C. orthopsilosis suggest that the former species may have evolved very recently from the latter.

FIG. 1.

RAPD patterns produced for 32 C. parapsilosis strains with the primer RPO2. Lanes 1 and 2, RAPD representative profiles obtained for all C. parapsilosis group I isolates (profile A); lanes 3 to 11, C. parapsilosis group II isolates (B1 to B4 profiles); lanes 12 and 13, C. parapsilosis group III isolates (profile C). M, 100-bp ladder.

FIG. 2.

Unrooted radial tree showing nearest-neighbor clustering of sequence polymorphism data for COX3, SADH, and SYA1 genes. All 32 test isolates were sequenced, but sequences were identical for the 21 group I isolates and the 2 group III isolates, which are therefore shown as single entities. Bootstrap values are indicated at the nodes.

FIG. 3.

(a) SADH fragment amplification (expected PCR product of 716 bp) in different Candida species: lane 1, C. albicans; lane 2, C. dubliniensis; lane 3, C. famata; lane 4, C. glabrata; lane 5, C. guilliermondii; lane 6, C. kefyr; lane 7, C. krusei; lane 8, C. lusitaniae; lane 9, C. metapsilosis; lane 10, C. orthopsilosis; lane 11, C. parapsilosis; lane 12, C. tropicalis. Lane 13, S. cerevisiae; lane M, 100-bp ladder. (b) BanI restriction digestion of SADH-PCR product obtained from representative C. metapsilosis (lane 1), C. orthopsilosis (lane 2), and C. parapsilosis (lane 3) strain types. Lane M, 100-bp ladder.

FIG. 4.

Phylogenetic neighbor-joining tree generated from a genetic similarity matrix based on comparison of ITS1 sequences. Numbers at each node indicate similarity percentage.