''Kluyveromyces marxianus'' in

ascomycetous Ascomycota is a phylum of the kingdom Fungi that, together with the Basidiomycota, forms the subkingdom Dikarya. Its members are commonly known as the sac fungi or ascomycetes. It is the largest phylum of Fungi, with over 64,000 species. The def ...

yeast Yeasts are eukaryotic, single-celled microorganisms classified as members of the fungus kingdom (biology), kingdom. The first yeast originated hundreds of millions of years ago, and at least 1,500 species are currently recognized. They are est ...

and member of the genus, ''Kluyveromyces''. It is the sexual stage (teleomorph) of ''Atelosaccharomyces pseudotropicalis'' also known as ''

Candida Candida, or Cándida (Spanish), may refer to: Biology and medicine * ''Candida'' (fungus), a genus of yeasts ** Candidiasis, an infection by ''Candida'' organisms * Malvasia Candida, a variety of grape Places * Candida, Campania, a ''comu ...

kefyr''. This species has a

homothallic In fungi and algae, homothallism refers to the condition in which a single individual or thallus carries the genetic determinants (i.e., both mating types or sexes) required to undergo sexual reproduction without the need for a distinct mating partn ...

mating system and is often isolated from

dairy product Dairy products or milk products are food products made from (or containing) milk. The most common dairy animals are cow, water buffalo, goat, nanny goat, and Sheep, ewe. Dairy products include common grocery store food around the world such as y ...

History

Taxonomy

This species was first described in the genus ''

Saccharomyces ''Saccharomyces'' is a genus of fungi that includes many species of yeasts. ''Saccharomyces'' is from Greek σάκχαρον (sugar) and μύκης (fungus) and means ''sugar fungus''. Many members of this genus are considered very important in f ...

'' as ''S. marxianus'' by the Danish mycologist,

Emil Christian Hansen Emil Christian Hansen (8 May 1842 – 27 August 1909) was a Danish mycologist and fermentation physiologist. Early life and education Hansen was born in Ribe to Joseph Christian Hansen, a house-painter, and his wife Ane Catherina Dyhre. Be ...

from beer wort. He named the species for the zymologist, Louis Marx of

Marseille Marseille (; ; see #Name, below) is a city in southern France, the Prefectures in France, prefecture of the Departments of France, department of Bouches-du-Rhône and of the Provence-Alpes-Côte d'Azur Regions of France, region. Situated in the ...

who first isolated it from

grape A grape is a fruit, botanically a berry, of the deciduous woody vines of the flowering plant genus ''Vitis''. Grapes are a non- climacteric type of fruit, generally occurring in clusters. The cultivation of grapes began approximately 8,0 ...

. The species was transferred to the genus ''Kluyveromyces'' by van der Walt in 1956. Since then, 45 species have been recognized in this genus. The anamorphic

basionym In the scientific name of organisms, basionym or basyonym means the original name on which a new name is based; the author citation of the new name should include the authors of the basionym in parentheses. The term "basionym" is used in both botan ...

''Saccharomyces kefyr'' was created by

Martinus Beijerinck Martinus Willem Beijerinck (, 16 March 1851 – 1 January 1931) was a Dutch microbiologist and botanist who was one of the founders of virology and environmental microbiology. He is credited with the co-discovery of viruses A virus i ...

in 1889 in an article titled ''Sur le kéfir'' ("On

kefir Kefir ( ; alternative spellings: kephir or kefier; ; ; ) is a Fermented milk products, fermented milk drink similar to a thin yogurt or ayran that is made from kefir grains, a specific type of mesophilic SCOBY, symbiotic culture. It is prep ...

" in English); the type material is a grain of kefir. The other commonly-used anamorphic basionym ''Endomyces pseudotropicalis'' was coined by Castell. in 1911, its type strain having been isolated from a Sri Lankan patient.

Phylogeny

The closest relative of ''Kluyveromyces marxianus'' is the yeast ''

Kluyveromyces lactis ''Kluyveromyces lactis'' is a ''Kluyveromyces'' yeast commonly used for genetic studies and industrial applications. Its name comes from the ability to assimilate lactose and convert it into lactic acid. ''Kluyveromyces lactis'' (formerly ''Sac ...

'', often used in the dairy industry. Both ''

Kluyveromyces ''Kluyveromyces'' is a genus of ascomycetous yeasts in the family Saccharomycetaceae. Some of the species, such as ''Kluyveromyces marxianus, K. marxianus'', are the teleomorphs of ''Candida (genus), Candida species''. The genus name of ''Kluyve ...

'' and ''

'' are considered a part of the "''Saccharomyces'' complex", subclade of the

Saccharomycetes Saccharomycetes belongs to the Ascomycota division of the kingdom Fungi. It is the only class in the subdivision Saccharomycotina, the budding yeast Yeasts are eukaryotic, single-celled microorganisms classified as members of the fungus kin ...

. Using

18S rRNA 18S ribosomal RNA (abbreviated 18S rRNA) is a part of the ribosomal RNA in eukaryotes. It is a component of the Eukaryotic small ribosomal subunit (40S) and the cytosolic homologue of both the 12S rRNA in mitochondria and the 16S rRNA in plas ...

gene sequencing, it was suggested that ''K. marxianus'', ''K. aestuarii'', ''K. dobzhanskii'', ''K. lactic'', ''K. wickerhamii'', ''K. blattae'', ''K. thermotolerans'', and ' collectively constituted a distinct

clade In biology, a clade (), also known as a Monophyly, monophyletic group or natural group, is a group of organisms that is composed of a common ancestor and all of its descendants. Clades are the fundamental unit of cladistics, a modern approach t ...

of separate ancestry from the central clade in the genus ''Kluyveromyces''. Within this complex, two categories are defined based on the presence in certain taxa of a whole-genome duplication event: the two clades are referred to as pre-Whole Genome Duplication (WGD) and post-WGD. ''Kluyveromyces'' species are affiliated with the first of this clades while species of ''Saccharomyces'' belong to the latter. Separation of these clades based on the presence of the WGD event explains why, even though the two species are closely related, fundamental differences exist between them.

Growth and morphology

Colonies of ''K. marxianus'' are cream to brown in colour with the occasional pink pigmentation due to production of the

iron chelate Ferric EDTA is the coordination complex formed from ferric ions and EDTA. EDTA has a high affinity for ferric ions. It gives yellowish aqueous solutions. Synthesis and structure Solutions of Fe(III)-EDTA are produced by combining ferrous salts a ...

pigment, pulcherrimin. When grown on Wickerham's Yeast-Mold (YM) agar, the yeast cells appear globose,

ellipsoidal An ellipsoid is a surface that can be obtained from a sphere by deforming it by means of directional scalings, or more generally, of an affine transformation. An ellipsoid is a quadric surface; that is, a surface that may be defined as the ze ...

or cylindrical, 2–6 x 3–11 μm in size. In a glucose-yeast extract broth, ''K. marxianus'' grows to produce a ring composed of sediment. A thin pellicle may be formed. In a Dalmau plate culture containing

cornmeal Maize meal is a meal (coarse flour) ground from dried maize. It is a common staple food and is ground to coarse, medium, and fine consistencies, but it is not as fine as wheat flour can be.Herbst, Sharon, ''Food Lover's Companion'', Third Editi ...

agar and

Polysorbate 80 Polysorbate 80 is a nonionic surfactant and emulsifier often used in pharmaceuticals, foods, and cosmetics. This synthetic compound is a viscous, water-soluble yellow liquid. Chemistry Polysorbate 80 is derived from polyethoxylated sorbitan ...

, ''K. marxianus'' forms a rudimentary to branched pseudomycelium with few

blastospore A blastospore is an asexual reproductive spore produced by budding, commonly found in fungi within the division Glomeromycota. The word blastospore is derived from the Greek ('sprout', 'bud', or 'germ') and ('spore'). In ''Candida albica ...

s. ''K. marxianus'' is thermotolerant, exhibiting a high growth rate at .

Physiology and reproduction

''Kluyveromyces marxianus'' is an aerobic yeast capable of respiro-fermentative metabolism that consists of simultaneously generating energy from both respiration via the TCA cycle and

ethanol fermentation Ethanol fermentation, also called alcoholic fermentation, is a biological process which converts sugars such as glucose, fructose, and sucrose into cellular energy, producing ethanol and carbon dioxide as by-products. Because yeasts perform this ...

. The balance between respiration and fermentation metabolisms is strain specific. This species also ferments inulin, glucose, raffinose, sucrose and lactose into ethanol. ''K. marxianus'' is widely used in industry because of its ability to use

lactose Lactose is a disaccharide composed of galactose and glucose and has the molecular formula C12H22O11. Lactose makes up around 2–8% of milk (by mass). The name comes from (Genitive case, gen. ), the Latin word for milk, plus the suffix ''-o ...

. Two genes, ''LAC12'' and ''LAC4'', allow ''K. marxianus'' to absorb and use lactose as a carbon source. This species is considered to be a " crabtree negative fungus", meaning it is unable to convert sugars into ethanol as effectively as crabtree positive taxa such as ''

S. cerevisiae ''Saccharomyces cerevisiae'' () (brewer's yeast or baker's yeast) is a species of yeast (single-celled fungal microorganisms). The species has been instrumental in winemaking, baking, and brewing since ancient times. It is believed to have been o ...

''. Studies, however, deem it to be crabtree positive which is likely due to strain differences since ''K. marxianus'' possesses the necessary genes to be crabtree positive. ''K. marxianus'' is highly thermotolerant and able to withstand temperatures up to . ''K. marxianus'' is also able to use multiple carbon substrata at the same time making it highly suited to industrial use. When glucose concentrations become depleted to 6 g/L, the lactose co-transport initiates. The formation of the ascospores occurs through the conjugation of the haploid cells preceding the formation of the ascus. Alternatively, ascosporogensis can arise directly from diploid cells. Each

ascus An ascus (; : asci) is the sexual spore-bearing cell produced in ascomycete fungi. Each ascus usually contains eight ascospores (or octad), produced by meiosis followed, in most species, by a mitotic cell division. However, asci in some gen ...

contains 1–4 ascospores. The

ploidy Ploidy () is the number of complete sets of chromosomes in a cell, and hence the number of possible alleles for autosomal and pseudoautosomal genes. Here ''sets of chromosomes'' refers to the number of maternal and paternal chromosome copies, ...

of ''K. marxianus'' was originally thought to be a haploid but recent research has shown that many strains used in research and industry are diploid. These conflicting findings suggest that ''K. marxianus'' can exist in vegetative form either as a haploid and a diploid.

Habitat and ecology

''Kluyveromyces marxianus'' has been isolated in dairy products, sisal leaves, and sewage from sugar manufacturing factories. It is also a naturally occurring colonist of plants, including corn.

Human disease

''Kluyveromyces marxianus'' is not usually an agent of human disease, although infection in humans can occur in immunocompromised individuals. This species has been associated with

candidemia Fungemia is the presence of fungi or yeast in the blood. The most common type, also known as candidemia, candedemia, or systemic candidiasis, is caused by '' Candida'' species. Candidemia is also among the most common bloodstream infections ...

and has been recovered from

catheter In medicine, a catheter ( ) is a thin tubing (material), tube made from medical grade materials serving a broad range of functions. Catheters are medical devices that can be inserted in the body to treat diseases or perform a surgical procedure. ...

s. It has also found in

biofilm A biofilm is a Syntrophy, syntrophic Microbial consortium, community of microorganisms in which cell (biology), cells cell adhesion, stick to each other and often also to a surface. These adherent cells become embedded within a slimy ext ...

s on other indwelling devices such as

pacemakers A pacemaker, also known as an artificial cardiac pacemaker, is an implanted medical device that generates electrical pulses delivered by electrodes to one or more of the chambers of the heart. Each pulse causes the targeted chamber(s) to co ...

and prosthetic heart valves. Between 1–3 % of cases involving ''K. marxianus'' that have been reported oncology patients, surgical wards, female genital infections and upper respiratory infections. Treatment with

amphotericin B Amphotericin B is an antifungal medication used for serious fungal infections and leishmaniasis. The fungal infections it is used to treat include mucormycosis, aspergillosis, blastomycosis, candidiasis, coccidioidomycosis, and cryptococ ...

have been effective against ''K. marxianus'' in one case report.

Industrial applications

Industrial use of ''K. marxianus'' is chiefly in the conversion of lactose to

ethanol Ethanol (also called ethyl alcohol, grain alcohol, drinking alcohol, or simply alcohol) is an organic compound with the chemical formula . It is an Alcohol (chemistry), alcohol, with its formula also written as , or EtOH, where Et is the ps ...

as a precursor for the production of

biofuel Biofuel is a fuel that is produced over a short time span from Biomass (energy), biomass, rather than by the very slow natural processes involved in the formation of fossil fuels such as oil. Biofuel can be produced from plants or from agricu ...

. The ability for ''K. marxianus'' to reduce lactose is useful because of the potential to transform industrial whey waste, a problematic waste product for disposal, into useful biomass for animal feed, food additives or fuel. Certain strains of the fungus can also be used to convert whey to ethyl acetate, an alternative fuel source. ''K. marxianus'' is also used to produce the

industrial enzymes Industrial enzymes are enzymes that are commercially used in a variety of industries such as pharmaceuticals, chemical production, biofuels, food and beverage, and consumer products. Due to advancements in recent years, biocatalysis through isolat ...

inulinase Inulinase ( and , inulase, endoinulinase, endo-inulinase, exoinulinase, 2,1-β-D-fructan fructanohydrolase) is an enzyme with systematic name 1-β-D-fructan fructanohydrolase. It catalyses the reaction: : Endohydrolysis of (2→1)-β-D-fructos ...

β-galactosidase β-Galactosidase (EC 3.2.1.23, beta-gal or β-gal; systematic name β-D-galactoside galactohydrolase) is a glycoside hydrolase enzyme that catalyzes hydrolysis of terminal non-reducing β-D-galactose residues in β-D-galactosides. (This enzym ...

, and

pectinase Pectinases are a group of enzymes that breaks down pectin, a polysaccharide found in plant cell walls, through hydrolysis, transelimination and deesterification reactions. Commonly referred to as pectic enzymes, they include pectolyase, pectozym ...

. Due to the heat tolerance of ''K. marxianus'', high heat fermentations are feasible, reducing the costs normally expended for cooling as well as the potential for contamination by other fungi or bacteria. In addition, fermentations at higher temperatures occur more rapidly, making production much more efficient. Due to the ability of ''K. marxianus'' to simultaneously utilize lactose and glucose, the prevalence of ''K. marxianus'' in industrial settings is high as it decreases production time and increases productivity. Recent efforts have attempted to use ''K. marxianus'' in the production of food flavourings from waste products tomato and pepper pomaces as substrata.

References

External links

* {{Authority control Yeasts Saccharomycetaceae Fungi described in 1888 Fungus species