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Delimitation of the species of the Debaryomyces hansenii complex by intron sequence analysis

CIRM-Levures, Laboratoire de Microbiologie et Génétique Moléculaire, INRA, CNRS, AgroParisTech, 78850 Thiverval-Grignon, France

Correspondence
Serge Casaregola
serge.casaregola{at}grignon.inra.fr

The delineation of species among strains assigned to Debaryomyces hansenii was examined using a gene genealogies-based approach in order to compare spliceosomal intron sequences found in four housekeeping genes (ACT1, TUB2, RPL31 and RPL33). This revealed four distinct groups of strains containing, respectively, D. hansenii var. hansenii CBS 767^T, D. hansenii var. fabryi CBS 789^T, Candida famata var. flareri CBS 1796^T (the anamorph of D. hansenii var. fabryi CBS 789^T) and Debaryomyces tyrocola CBS 766^T, whose species status was no longer accepted. The sequence divergence between these groups, reaching in some cases over 20 %, unambiguously isolated the groups as separate taxa, leading to a proposal for the reinstatement of the originally described species D. hansenii CBS 767^T and D. tyrocola CBS 766^T. The variety D. hansenii var. fabryi was further subdivided into two taxa, Debaryomyces fabryi CBS 789^T and Candida flareri CBS 1796^T (previously C. famata var. flareri and Blastodendrion flareri). The comparison of intron sequences therefore exposed cryptic species whose phenotypic traits are not distinguishable from known species, but which have significantly diverged from the genetic point of view. Hence, we describe the new taxon Debaryomyces macquariensis sp. nov. CBS 5571^T is related to, but clearly distinct from, the Debaryomyces species mentioned above. The approach used in this work has also revealed the existence of populations within the newly delineated species D. hansenii and genetic exchanges between these populations, indicating an unexpected genetic diversity within this part of the genus Debaryomyces.

The GenBank/EMBL/DDBJ accession numbers for sequences described in this article are: for the ACT1 introns, AM990068–AM990117; for the RPL31 introns, AM990118–AM990167; for the RPL33 introns, AM990543–AM990594; for the TUB2 introns, AM990595–AM990641, FM165416 for the CBS 7761 ACT1 coding gene and FM165417 for the CBS 5572 ACT1 coding gene. The MycoBank (http://www.mycobank.org) accession number for Debaryomyces macquariensis sp. nov. is MB 512270.

Supplementary tables showing the primers used in this study and the sequence divergence within the ACT1 gene intron between clades and species are available with the online version of this paper.