Eukaryotes Genomes - DEBARYOMYCES HANSENII

Debaryomyces ( Torulaspora) hansenii is a cryotolerant (frost resistant), marine yeast, which can tolerate salinity levels up to 24%,

Cryo- and osmotolerance (pressure change tolerant) account for its important role in several agro-food processes. D. hansenii is the most common species of yeast found in all types of cheeses, unlike other species, the prevalence of which is cheese dependent D. hansenii is also common in dairies and in brine because it is able to grow in the presence of salt at low temperature and to metabolise lactic and citric acids. D. hansenii also provides proteolytic and lipolytic activities during cheese ripening.

D. hansenii is one of the most frequent yeast species to be associated with chilled food and although normally considered as non-pathogenic, one case of bone infection associated with this yeast was reported and several clinical samples were identified as D. hansenii (and its anamorph Candida famata ) in superficial infections. D. hansenii is also an alkane-assimilating yeast.

Complete sequencing and comparison of four hemiascomycetous yeasts has been undertaken these are: Candida glabrata, Kluyveromyces lactis, Debaryomyces hansenii, and Yarrowia lipolytica. They were selected on the basis of their phylogenetic positions and their specific interest as human pathogens, or as industrially or environmentally important yeast s. D. hansenii was selected because it is a halotolerant yeast, related to C. albicans and other pathogenic yeasts, that is often found on fish and salted dairy products.

Important for evolutionary studies, the four yeast species display different mechanisms of sexuality, Yarrowia lipolytica has a haplo-diplontic cycle (that is, it alternates between haploid and diploid phases of similar importance), whereas D. hansenii is a homothallic yeast with an essentially haplontic life cycle. Both species have only one mating-type locus, whereas the other two have two silent mating-type cassette homologues, similar to S. cerevisiae.

The sequence of the genome of the type strain D. hansenii CBS767 revealed that the genome is made of seven chromosomes ranging from 1.25 Mb to 2.33 Mb with a total size of 12.2 Mb.

D. hansenii seems to have the highest coding capacity among yeasts, amounting to 79.2% of the genome with a putative number of 6906 detected CDS. D. hansenii is also the yeast with the most redundant genome with an overall redundancy of 49.2%.

This work, which represents the first multispecies exploration of genome evolution across an entire eukaryotic phylum, reveals the variety of events and mechanisms that have taken place, and should allow useful comparisons with other phyla of multicellular organisms when more genome sequences are determined.

References:

http://cbi.labri.u-bordeaux.fr/Genolevures/about.php