''Debaryomyces hansenii'' is a species of yeast in the family Saccharomycetaceae. Also known as ''Candida famata'', it accounts for up to 2% of invasive candidiasis cases.
Ecology
''Debaryomyces hansenii'' is an osmo-, halo- and xerotolerantyeast that produces toxins, including mycocins, to destroy competitive yeast species. It is a common species in all types of cheese, including soft cheeses and the brines of semi-hard and hard cheeses, and the most common yeast among 383 isolates from samples of unsulphited or sulphited sausages, skinless sausages and minced beef. It contributes to the fermentation of
barrel-aged beer
A barrel-aged beer is a beer that has been aged for a period of time in a wooden barrel. Typically, these barrels once housed bourbon, whisky, wine, or, to a lesser extent, brandy, sherry, or port.Harveys Brewery in southern England. Harvey's head brewer speculates that it is either airborne in the brewery or a slow-growing component of their house yeast blend. ''D. hansenii'' is also found in hyper-saline waters such as the salterns on the Atlantic coast of Namibia or in the
Great Salt Lake
The Great Salt Lake is the largest saltwater lake in the Western Hemisphere and the eighth-largest terminal lake in the world. It lies in the northern part of the U.S. state of Utah and has a substantial impact upon the local climate, particula ...
The species can be cultivated in media with up to 25% NaCl or 18% glycerol. Growth rate increases in solutions with ≥ 1 M NaCl or KCl, with sodium and potassium ions playing a very important role in the mechanisms involved in maintaining osmobalance. The species can survive a pH range between 3 and 10. Furthermore, ''D. hansenii'' has been described as the species with the highest perchlorate tolerance reported to date, which might have consequences for the microbial habitability of Mars, where perchlorate salts are widely distributed.
Reproduction
Most strains are
haploid
Ploidy () is the number of complete sets of chromosomes in a cell, and hence the number of possible alleles for autosomal and pseudoautosomal genes. Sets of chromosomes refer to the number of maternal and paternal chromosome copies, respectively ...
, mating very rarely and
diploid
Ploidy () is the number of complete sets of chromosomes in a cell, and hence the number of possible alleles for autosomal and pseudoautosomal genes. Sets of chromosomes refer to the number of maternal and paternal chromosome copies, respectively ...
ize transiently by somatogamous autogamy (i.e. fusion of two cells but excluding their nuclei). Sexual reproduction proceeds via
heterogamous
Heterogamy is a term applied to a variety of distinct phenomena in different scientific domains. Usually having to do with some kind of difference, "hetero", in reproduction, "gamy". See below for more specific senses.
Science Reproductive biolog ...
conjugation (i.e. the conjugation of two cells of different form or size) leading to short diplophase followed by meiosis and ascospore formation. Haploid yeasts reproduce vegetatively by multilateral budding.
Genetics
This species has seven chromosomes, labeled A-G. This species uses an alternative genetic code for the codon CUG, coding for the amino acid serine instead of the usual leucine.
Differentiation
The ability of this species to grow at 10% NaCl or 5% glucose is used to discriminate ''D. hansenii'' from other ascomycetous yeasts. The species comprises two varieties: ''D. hansenii'' var. ''hansenii'' and var. ''fabryii''. These two groups can be differentiated via rRNA, the electrophoretic mobility of their glucose-6-phosphate dehydrogenase, or by their maximum grow temperatures (35 °C for var. ''hansenii'' and 39 °C for var. ''fabryii'').
Biotechnology
The species has been demonstrated to synthesize useful quantities of
D-arabinitol
Arabitol, or arabinitol, is a sugar alcohol. It can be formed by the reduction of either arabinose or lyxose. Some organic acid tests check for the presence of D-arabitol, which may indicate overgrowth of Gut flora, intestinal microbes such as ''C ...
,
riboflavin
Riboflavin, also known as vitamin B2, is a vitamin found in food and sold as a dietary supplement. It is essential to the formation of two major coenzymes, flavin mononucleotide and flavin adenine dinucleotide. These coenzymes are involved in ...
pyruvic acid
Pyruvic acid (CH3COCOOH) is the simplest of the alpha-keto acids, with a carboxylic acid and a ketone functional group. Pyruvate, the conjugate base, CH3COCOO−, is an intermediate in several metabolic pathways throughout the cell.
Pyruvic aci ...
under thiamine
limitation. The species has also been used to
decarboxylate
Decarboxylation is a chemical reaction that removes a carboxyl group and releases carbon dioxide (CO2). Usually, decarboxylation refers to a reaction of carboxylic acids, removing a carbon atom from a carbon chain. The reverse process, which is t ...