Thermomyces lanuginosus

Thermomyces lanuginosus is a species of thermophilic fungus that belongs to Thermomyces, a genus of hemicellulose degraders. It is classified as a deuteromycete and no sexual form has ever been observed. It is the dominant fungus of compost heaps, due to its ability to withstand high temperatures and use complex carbon sources for energy. As the temperature of compost heaps rises and the availability of simple carbon sources decreases, it is able to out compete pioneer microflora. It plays an important role in breaking down the hemicelluloses found in plant biomass due to the many hydrolytic enzymes that it produces, such as lipolase, amylase, xylanase, phytase, and chitinase. These enzymes have chemical, environmental, and industrial applications due to their hydrolytic properties. They are used in the food, petroleum, pulp and paper, and animal feed industries, among others. A few rare cases of endocarditis due to T. lanuginosus have been reported in humans. The fungus was first described 1899 by Tsiklinskaya, after a chance discovery of it growing on a potato which had been inoculated with garden soil. It was later isolated in 1907 from leaves on warm compost piles by Hugo Miehe. Miehe was the first person to work with thermophilic microorganisms in his study of the spontaneous combustion of damp haystacks. T. lanuginosis was one of four species of thermophilic fungi isolated from self-heating hay by Miehe, along with Mucor pusillus, Thermoidium sulfureum, and Thermoascus aurantiacus. The fungus was also isolated by a number of different researchers. Griffon and Maublanc isolated it from fungus on moist oats in 1911, but placed it in the genus Sepedonium, as did Velich in 1914. Kurt Noack isolated several thermophilic fungi from natural habitats, including T. lanuginosis, studying their physiology further. Cooney and Emerson provided taxonomic descriptions of the 13 known fungal species during WWII, while studying alternate sources of rubber. This species has a number of synonyms, due to different names and categories being applied when it was first being described. Tsiklinskaya originally isolated and described the species, but failed to indicate the size of aleuriospores and didn't include drawings. Photographs of mycelium and spores were inconclusive because they didn't give a true picture of the size or structure due to failure in indicating the magnification. Due to this uncertainty, both Griffon and Maublanc (1911) and Velich (1914) placed it in the genus Sepedonium when they isolated and described it. It has also been placed in the Acremoniella category by Rege (1927) and Curzi (1929). In 1933 the name Montospora lanuginosa was proposed by Mason, but this was followed by a trend towards accepting the genus Humicola, as proposed by Bunce (1961) because of the questionable status of Montosporra. It was Pugh et al. who reintroduced the genus Thermomyces. Although the literature occasionally refers to this species by the earlier name Humicola lanuginosa, it is now uniformly referred to by its current name Thermomyces lanuginosa. The fungus has a number of important industrial applications because it produces the largest amounts of hydrolyzing enzymes of any thermophilic fungus. This has led to an interest in studying its genetics, and subsequently resulted in the sequencing of its genome. The proteome of T. lanuginosis contains 5100 genes, with 83 tRNA genes. One of the features that has been discovered through sequencing of the genome is that the fungus has a ubiquitin degradation pathway, which helps it respond to various environmental stressors, such as nutrient limitation, heat shock, and heavy metal exposure, and may be essential for adaptation during rising temperatures. It is also capable of histone acetylation/deacetylation and contains high numbers of methylases, which play important roles in packing and condensation of DNA. T. lanuginosus is classified as a thermophile, and experiences rapid growth at high temperatures. In the lab, colonies can be cultured in a glucose-salt liquid medium fortified with peptone. Colonies are white and velvety at first, generally less than 1 mm high, but soon turn grey or green-ish grey, starting from the center. Mature colonies are dull dark brown to black, often with pink or vinaceous diffusing pigment secreted from the colony. Masses of developing aleuriophores can be seen on the fine, colourless hyphae of young colonies when viewed under a microscope. These aleuriophores are short, measure 10-15μ in length, and arise at right angles to the hyphae. They are generally unbranched but occasionally branch once or twice near the base, appearing as a cluster. Septations may occur but are often difficult to observe. Aleuriospores are borne singly at tips of the aleuriophores. No teleomorph is known for this species. The asexual conida are borne singly on short stalks and are one celled, dark brown, with a roughened surface. Spores are colorless and smooth at first, but turn dark brown during maturation, and the thick exospore becomes wrinkled. Mature spores are spherical, irregularly shaped, and range from 6-10 μ in diameter. Both immature and mature spores can be easily separated from the aleuriophore, which usually ruptures slightly below the point of attachment, so free spores may be found with the top portion still attached.