|Rhodotorula mucilaginosa cells, Methylene blue stain, magnification 400x|
(Fresen.) F.C.Harrison (1928)
Rhodotorula is a genus of pigmented yeasts, part of the division Basidiomycota. It is readily identifiable by distinctive orange/red colonies when grown on Sabouraud's dextrose agar (SDA). This distinctive color is the result of pigments that the yeast creates to block out certain wavelengths of light (620–750 nm) that would otherwise be damaging to the cell.
Rhodotorula is a common environmental inhabitant. It can be cultured from soil, water, milk, fruit juice, and air samples. It is able to scavenge nitrogenous compounds from its environment remarkably well, growing even in air that has been carefully cleaned of any fixed nitrogen contaminants. In such conditions, the nitrogen content of the dry weight of Rhodotorula can drop as low as 1%, compared to around 14% for most bacteria growing in normal conditions.
Only Rhodotorula mucilaginosa, R. glutinis, and R. minuta have been known to cause disease in humans. There were no reported cases of Rhodotorula infections before 1985. There were however forty-three reported cases of Rhodotorula bloodstream infections (BSIs) between 1960 and 2000. Rhodotorula is most commonly found in patients who are immunosuppressed and/or are using foreign-body technology such as central venous catheters. Rhodotorula is commonly treated by removing the catheter and the use of anti-fungals. Rhodotorula is susceptible to amphotericin B and flucytosine.
Rhodotorula can also cause infections in animals. There have been reports of skin infections in chickens and sea animals and lung infections and otitis in sheep and cattle.
One area in which Rhodotorula species may become of importance is in bioremediation, especially of contaminated water sites. As with bacteria, fungi can naturally develop modified metabolism to deal with environmental contaminants, and could then be used in bioremediation. One main target is often polycyclic aromatic hydrocarbons (PAHs) since they often persist in the environment and have high levels of toxicity. Through sediment analysis and testing of contaminated waters Rhodotorula were found to be common in contaminated sites. It was noted in samples taken from contaminated waters that Rhodotorula species had the ability to degrade petroleum compounds. These studies as well as others suggest that Rhodotorula species may be good candidates for bioremediation of polluted waters for PAHs. In more directed studies a number of species of Rhodotorula were found to be able to degrade a number of specific contaminants. For example, R. glutinis and R. rubra have both been found to have a high ability to degrade phenanthrene, while R. minuta has been found to degrade benzo(a)anthracene. In a mixed fungal community Rhodotorula species contributed to effective degradation of low molecular weight PAHs, and although bacterial communities alone were not able to, the fungal communities also degraded high molecular weight PAHs (more than 3 benzene rings) such as chrysene and benzo(a)pyrene. A strain of R. taiwanensis was shown to grow at constant gamma radiation 66 Gy/h at pH 2.3 and in the presence of high concentrations of mercury and chromium compounds, and forming biofilms under high-level chronic radiation and low pH, making it a promising candidate for bioremediation of acidic radioactive waste sites.