Rhodotorula Glutinis
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''Rhodotorula glutinis'' is the
type species In International_Code_of_Zoological_Nomenclature, zoological nomenclature, a type species (''species typica'') is the species name with which the name of a genus or subgenus is considered to be permanently taxonomically associated, i.e., the spe ...
of the genus ''
Rhodotorula ''Rhodotorula'' is a genus of fungi in the class (biology), class Microbotryomycetes. Most species are known in their yeast states which produce orange to red colony (biology), colonies when grown on Sabouraud agar, Sabouraud's dextrose agar (SD ...
'', a basidiomycetous genus of pink
yeasts Yeasts are eukaryotic, single-celled microorganisms classified as members of the fungus kingdom. The first yeast originated hundreds of millions of years ago, and at least 1,500 species are currently recognized. They are estimated to constitu ...
which contains 370 species. Heterogeneity of the genus has made its classification difficult with five varieties having been recognized; however, as of 2011, all are considered to represent a single
taxon In biology, a taxon (back-formation from ''taxonomy''; : taxa) is a group of one or more populations of an organism or organisms seen by taxonomists to form a unit. Although neither is required, a taxon is usually known by a particular name and ...
. The fungus is a common
colonist A settler or a colonist is a person who establishes or joins a permanent presence that is separate to existing communities. The entity that a settler establishes is a settlement. A settler is called a pioneer if they are among the first settli ...
of animals, foods and environmental materials. It can cause
opportunistic infection An opportunistic infection is an infection that occurs most commonly in individuals with an immunodeficiency disorder and acts more severe on those with a weakened immune system. These types of infections are considered serious and can be caused b ...
s, notably blood infection in the setting of significant underlying disease. It has been used industrially in the production of
carotenoid Carotenoids () are yellow, orange, and red organic pigments that are produced by plants and algae, as well as several bacteria, archaea, and fungi. Carotenoids give the characteristic color to pumpkins, carrots, parsnips, corn, tomatoes, cana ...
pigments and as a biocontrol agent for post-harvest spoilage diseases of fruits.


Growth and morphology

''Rhodotorula glutinis'' is an aerobic yeast characterized by pink, smooth colonies with a moist appearance. Reproduction is typically by multipolar
budding Budding or blastogenesis is a type of asexual reproduction in which a new organism develops from an outgrowth or bud due to cell division at one particular site. For example, the small bulb-like projection coming out from the yeast cell is kno ...
although
pseudohyphae A hypha (; ) is a long, branching, filamentous structure of a fungus, oomycete, or actinobacterium. In most fungi, hyphae are the main mode of vegetative growth, and are collectively called a mycelium. Structure A hypha consists of one o ...
are occasionally produced. Sexual reproduction is by basidiospores arising from a
teliospore Teliospore (sometimes called teleutospore) is the thick-walled resting spore of some fungi (Rust (fungus), rusts and Smut (fungus), smuts), from which the basidium arises. Development They develop in ''telium, telia'' (sing. ''telium'' or ''telio ...
developed from a mycelial clamp connection. A distinguishing feature of the species and its close relatives are the intense yellow and red pigments produced during growth on most substrates. It normally grows at 37 °C at a rapid rate, and requires a minimum
water activity In food science, water activity (''aw'') of a food is the ratio of its vapor pressure to the vapor pressure of water at the same temperature, both taken at equilibrium. Pure water has a water activity of one. Put another way, ''aw'' is the equi ...
of 0.92, pH of 2.2, and organic acids or HCl. Growth is inhibited by 100 mg/kg or less of
benzoic acid Benzoic acid () is a white (or colorless) solid organic compound with the formula , whose structure consists of a benzene ring () with a carboxyl () substituent. The benzoyl group is often abbreviated "Bz" (not to be confused with "Bn," which ...
or
sorbic acid Sorbic acid, or 2,4-hexadienoic acid, is a natural organic compound used as a food preservative. It has the chemical formula and the structure . It is a colourless solid that is slightly soluble in water and sublimes readily. It was first iso ...
and a pH of 4 or above. The fungus is unable to grow on malt acetic agar or MY50G medium. At maturity, the cells reach a diameter of 3-5 μm and are round, oval, or elongate in shape, aggregating as mucoid colonies.
Carbohydrates A carbohydrate () is a biomolecule composed of carbon (C), hydrogen (H), and oxygen (O) atoms. The typical hydrogen-to-oxygen atomic ratio is 2:1, analogous to that of water, and is represented by the empirical formula (where ''m'' and ''n'' ma ...
in the cell include glucose,
fucose Fucose is a hexose deoxy sugar with the chemical formula C6H12O5. It is found on ''N''-linked glycans on the mammalian, insect and plant cell surface. Fucose is the fundamental sub-unit of the seaweed polysaccharide fucoidan. The α(1→3) l ...
, galactose, and
mannose Mannose is a sugar with the formula , which sometimes is abbreviated Man. It is one of the monomers of the aldohexose series of carbohydrates. It is a C-2 epimer of glucose. Mannose is important in human metabolism, especially in the glycosylatio ...
. ''R. glutinis'' is heat resistant, an uncommon feature in yeasts without spores, tolerating for 10 minutes. R. ''glutinis'' is closely related to ''Rhodotorula mucilaginosa'', differing only in their ability to use
nitrate Nitrate is a polyatomic ion with the chemical formula . salt (chemistry), Salts containing this ion are called nitrates. Nitrates are common components of fertilizers and explosives. Almost all inorganic nitrates are solubility, soluble in wa ...
as a nitrogen source, which ''R. glutinis'' cannot assimilate. Both species are incapable of fermentation and assimilation of Myo-Inositol and D-glucoronate. Standard microbiological methods of identification have misidentified '' Candida auris'' as ''Rhodotorula glutinis'', until
sequence analysis In bioinformatics, sequence analysis is the process of subjecting a DNA, RNA or peptide sequence to any of a wide range of analytical methods to understand its features, function, structure, or evolution. It can be performed on the entire genome ...
correctly identified ''C. auris'' as such. The genome of ''R. glutinis'' is CG-rich, containing up to 67% GC by base composition.


Habitat and ecology

''Rhodotorula glutinis'' is distributed widely, most often found in soil, air and throughout the phyllosphere. Accordingly, it is not uncommon to recover it in cultures of cereals, flour, malting
barley Barley (), a member of the grass family, is a major cereal grain grown in temperate climates globally. It was one of the first cultivated grains; it was domesticated in the Fertile Crescent around 9000 BC, giving it nonshattering spikele ...
, dough, citrus products,
olives The olive, botanical name ''Olea europaea'' ("European olive"), is a species of Subtropics, subtropical evergreen tree in the Family (biology), family Oleaceae. Originating in Anatolia, Asia Minor, it is abundant throughout the Mediterranean ...
and soaking
soybeans The soybean, soy bean, or soya bean (''Glycine max'') is a species of legume native to East Asia, widely grown for its edible bean. Soy is a staple crop, the world's most grown legume, and an important animal feed. Soy is a key source of f ...
. It is frequently isolated from foods. Due to its rapid growth at refrigerator temperatures, it is encountered sometimes as a spoilage agent in dairy products such as yogurts, cheeses,
butter Butter is a dairy product made from the fat and protein components of Churning (butter), churned cream. It is a semi-solid emulsion at room temperature, consisting of approximately 81% butterfat. It is used at room temperature as a spread (food ...
, and fresh and processed meats, vegetables and seafoods. It has also been reported from blotched frozen
peas Pea (''pisum'' in Latin) is a pulse or fodder crop, but the word often refers to the seed or sometimes the pod of this flowering plant species. Peas are eaten as a vegetable. Carl Linnaeus gave the species the scientific name ''Pisum sativum ...
stored at for 8 weeks with yeast burden increasing significantly after 24 weeks at , suggesting an ability to proliferate at temperatures below freezing. The fungus is a
commensal Commensalism is a long-term biological interaction (symbiosis) in which members of one species gain benefits while those of the other species neither benefit nor are harmed. This is in contrast with mutualism, in which both organisms benefit f ...
of mammals including humans, occurring commonly on skin and is found in stool.


Industrial applications

There has been increasing interest and development in the biotechnological applications of ''R. glutinis'' over recent years. The fungus produces
carotenoids Carotenoids () are yellow, orange, and red organic compound, organic pigments that are produced by plants and algae, as well as several bacteria, archaea, and Fungus, fungi. Carotenoids give the characteristic color to pumpkins, carrots, parsnips ...
, such as beta-Carotene and torularhodin, which animals cannot synthesize on their own. In the yeast, carotenoids act as a protective agent against visible light and harmful metabolic
oxygen Oxygen is a chemical element; it has chemical symbol, symbol O and atomic number 8. It is a member of the chalcogen group (periodic table), group in the periodic table, a highly reactivity (chemistry), reactive nonmetal (chemistry), non ...
species. Carotenoids are valuable in
wastewater treatment Wastewater treatment is a process which removes and eliminates contaminants from wastewater. It thus converts it into an effluent that can be returned to the water cycle. Once back in the water cycle, the effluent creates an acceptable impact on ...
, production of
enzymes An enzyme () is a protein that acts as a biological catalyst by accelerating chemical reactions. The molecules upon which enzymes may act are called substrates, and the enzyme converts the substrates into different molecules known as pro ...
, pharmaceuticals, and even
tumor A neoplasm () is a type of abnormal and excessive growth of tissue. The process that occurs to form or produce a neoplasm is called neoplasia. The growth of a neoplasm is uncoordinated with that of the normal surrounding tissue, and persists ...
inhibition. Because the fungus exhibits rapid growth and is ostensibly
single-celled A unicellular organism, also known as a single-celled organism, is an organism that consists of a single cell (biology), cell, unlike a multicellular organism that consists of multiple cells. Organisms fall into two general categories: prokaryotic ...
, it is a potential candidate for large-scale manufacturing. Given a suitable culture medium, an optimal yield of carotenoid could in theory be attained from cheap substrates such as
beet The beetroot (British English) or beet (North American English) is the taproot portion of a '' Beta vulgaris'' subsp. ''vulgaris'' plant in the Conditiva Group. The plant is a root vegetable also known as the table beet, garden beet, dinner ...
molasses,
peat Peat is an accumulation of partially Decomposition, decayed vegetation or organic matter. It is unique to natural areas called peatlands, bogs, mires, Moorland, moors, or muskegs. ''Sphagnum'' moss, also called peat moss, is one of the most ...
extract, and grape must. An ''R. glutinis'' mutant (NCIM 3253) was shown to produce 76-fold more b-carotene than their
wild type The wild type (WT) is the phenotype of the typical form of a species as it occurs in nature. Originally, the wild type was conceptualized as a product of the standard "normal" allele at a locus, in contrast to that produced by a non-standard, " ...
relatives, suggesting that these microorganisms may have a role in cost-effective, high yield manufacture of carotenoids. Recent studies have also shown that 16 strains of ''R. glutinis'' possess
antibacterial An antibiotic is a type of antimicrobial substance active against bacteria. It is the most important type of antibacterial agent for fighting bacterial infections, and antibiotic medications are widely used in the treatment and prevention ...
and
antioxidant Antioxidants are Chemical compound, compounds that inhibit Redox, oxidation, a chemical reaction that can produce Radical (chemistry), free radicals. Autoxidation leads to degradation of organic compounds, including living matter. Antioxidants ...
properties, although it is unclear if the fungus could be used to manufacture these materials on a commercially viable scale. ''R. glutinis'' has been investigated as a biocontrol agent of post-harvest disease of fruits. Pretreatment of apples and oranges with ''R. glutinis'' effectively reduced or prevented blue mold ('' Penicillium expansum'') and grey mold (''
Botrytis cinerea ''Botrytis cinerea'' is a necrotrophic fungus that affects many plant species, although its most notable hosts may be wine grapes. In viticulture, it is commonly known as "botrytis bunch rot"; in horticulture, it is usually called "grey mould" ...
''), lengthening the shelf life of these fruits without reducing fruit quality. The yeast is thought to inhibit post-spoilage rot by competing with spoilage agents for space and nutrients, i.e.
competitive inhibition Competitive inhibition is interruption of a chemistry, chemical pathway owing to one chemical substance inhibiting the effect of another by competing with it for molecular binding, binding or chemical bond, bonding. Any metabolism, metabolic or c ...
. An inoculum of ''R. glutinis'' remains viable in storage at for 5 days, supporting its potential as a stable biocontrol agent.


Pathogenicity

''Rhodotorula glutinis'' is the second most common disease-causing species of ''Rhodotorula'' following ''R. mucilaginosa''. Infections have been observed worldwide, though nearly half of all reported infections have originated in the Asia-Pacific region. It was not until 1985, that species of ''Rhodotorula'' had been first reported in human colonization and infection. Its occasional recovery from stool has led to the suggestion that it exists as a periodic, clinically insignificant colonist of the distal gut. ''Rhodotorula'' species are the most commonly isolated yeasts found on hands of hospital workers, suggesting a potential reservoir for the agent. This observation, combined with its high tolerance for extreme conditions may partially explain its rare appearance as an opportunistic agent of blood infection in seriously ill people. The majority of cases are systemic in nature, often causing fungemia in patients with underlying disease or
immunosuppression Immunosuppression is a reduction of the activation or efficacy of the immune system. Some portions of the immune system itself have immunosuppressive effects on other parts of the immune system, and immunosuppression may occur as an adverse react ...
, such as
cancer Cancer is a group of diseases involving Cell growth#Disorders, abnormal cell growth with the potential to Invasion (cancer), invade or Metastasis, spread to other parts of the body. These contrast with benign tumors, which do not spread. Po ...
or
leukemia Leukemia ( also spelled leukaemia; pronounced ) is a group of blood cancers that usually begin in the bone marrow and produce high numbers of abnormal blood cells. These blood cells are not fully developed and are called ''blasts'' or '' ...
, and transplant and
AIDS The HIV, human immunodeficiency virus (HIV) is a retrovirus that attacks the immune system. Without treatment, it can lead to a spectrum of conditions including acquired immunodeficiency syndrome (AIDS). It is a Preventive healthcare, pr ...
patients most likely to develop systemic infection. The incidence correlates with the rising use of intensive medical therapies and
central venous catheter A central venous catheter (CVC), also known as a central line (c-line), central venous line, or central venous access catheter, is a catheter placed into a large vein. It is a form of venous access. Placement of larger catheters in more centr ...
s. Infection may be linked to venous catheter contamination due to the strong affinity of this species for plastic. Although reports of systemic infections predominate, localized infection has been reported as well, including
meningitis Meningitis is acute or chronic inflammation of the protective membranes covering the brain and spinal cord, collectively called the meninges. The most common symptoms are fever, intense headache, vomiting and neck stiffness and occasion ...
and
peritonitis Peritonitis is inflammation of the localized or generalized peritoneum, the lining of the inner wall of the abdomen and covering of the abdominal organs. Symptoms may include severe pain, swelling of the abdomen, fever, or weight loss. One pa ...
absent overt immunosuppression or CVC. ''Rhodotorula glutinis'' is highly drug resistant to most
antifungal An antifungal medication, also known as an antimycotic medication, is a pharmaceutical fungicide or fungistatic used to treat and prevent mycosis such as athlete's foot, ringworm, candidiasis (thrush), serious systemic infections such as ...
agents, but successful treatment has been achieved 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 ...
.


References

{{Taxonbar, from=Q10653331 Sporidiobolales Fungi described in 1852 Fungal pathogens of humans Fungus species