Thermomyces lanuginosus

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.[2] It was later isolated in 1907 from leaves on warm compost piles by Hugo Miehe.[1] 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.[2]

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.[1] 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.[2]

This species has a number of synonyms, due to different names and categories being applied when it was first being described.[1][3] 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).[1]

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.[1] 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.[1][2]

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.[4]

Thermomyces lanuginosus is classified as a thermophile, and experiences rapid growth at high temperatures.[1] In the lab, colonies can be cultured in a glucose-salt liquid medium fortified with peptone.[2] 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.[5][1] Masses of developing aleuriophores can be seen on the fine, colourless hyphae of young colonies when viewed under a microscope.[1] 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.[1]

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.[5] 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.[1]

Thermophilic moulds grown at high temperatures (above 50 °C) contain dense body vesicles in their hyphae that function as storage organelles, mainly for phospholipids. In T. lanuginosus, nine times more lipid storage vesicles are grown at 52 °C than 37 °C. Heavy pigmentation of spores allows them to withstand temperature and heat stress, and the pigments have been found to be similar to hydroxylated pigments in aphids.[6]

Thermophilic fungi are primarily compost fungi, though T. lanuginosus has also been found to thrive in spoil tips, senescent grass leaves, sewage, and peat and bog soils, and is the dominant species of thermophilic fungi in hot springs.[6][7][14] Though it is sometimes found in soil, this is not a natural habitat for T. lanuginosus, and the concentration of spores of thermophilic fungi per gram material is approximately 10⁶ higher in composts than soils. It is proposed that their wide presence in soil is due to dispersal of spores elsewhere and fallout from air.[7]

Thermomyces lanuginosus has two of the most important qualities required for being a compost colonizer - it is able to withstand high temperatures and use complex carbon sources for energy.[9] It produces thermostable hemicellulases that degrade hemicellulose of plant biomass into simpler sugars.[15] As the temperature in compost systems rises, the pioneer flora disappears and thermophilic fungi become dominant.[14] Exothermic reactions of saprophytic and mesophilc microflora raise the temperature to 40 °C, which causes thermophilic spores to germinate and eventually outgrow pioneers, raising the temperature even higher to 60 °C.[2] Around the end of decomposition, thermophilic fungi compose 50-70% of compost biomass.[14] T. lanuginosus is a secondary sugar fungus and can participate in mutualistic relationships with some true cellulose decomposers of composts.[9]

Thermomyces lanuginosus Lipase (TLL) has a number of different chemical, environmental, and industrial applications, where hydrolytic processes are involved. Its regiospecificity allows the oleochemical industry to produce products such as cocoa butter equivalents, human milk fat substitutes, and other specific-structured lipids. It can be used for hydrolysis of oils and fats, alcoholysis or transesterifications of oils and fats, esterification of fatty acids, and acidolysis and interesterification of oils.[16]

The first commercialized lipase to be used in detergents was Lipolase, a fungal lipase initially derived from T. lanuginosus.[14] Lipases help the capability of detergent by removing stains. Lipolases have also been used in ionic liquids - environmentally attractive alternatives to typical organic solvents.[16]

TLL has many uses in organic chemistry, such in resolution of racemic mixtures, and creation of supercritical fluids. Large scale environmental applications include use in the degradation of polymers, treatment of wastewater from the meat industry, pretreatment of wool, and a sensor of fat quality in large scale processing.[16] The lipase has been found to be useful in the production of drugs and drug intermediates, such as anti-tumour agents, because it can help bring about kinetic resolutions of synthetically important chiral building blocks.[14] It also has applications in the petroleum industry as it can be used in the production of biodiesel.[16]

Endocarditis caused by the fungus has been reported in humans, but is very rare.[5] The first report of T. lanuginosus endocarditis was made postmortem over 25 years ago in a patient who had prior valvular surgery for Staphylococcus aureus infective endocarditis, where it remained asymptomatic for more than 6 months.[17][18] Another case was reported in an otherwise immunocompetent patient who had a prosthetic heart valve inserted following bacterial endocarditis. T. lanuginosus endocarditis was most likely the result of contamination during that surgery. In the latter case, the illness lasted 9 years and was treated with aggressive surgery and voriconaozle therapy.[17]

Risk factors for mould endocarditis include pre-existing lesions, valvular heart disease, prior cardiac surgery (such as valvular surgery, coronary artery bypass grafting, pacemaker or defibrillator insertion and surgery of the aorta) immunosuppression including pregnancy and prematurity, intravenous drug abuse, and having intravenous lines.[17][18] Symptoms at presentation may include fever, chills, cardiac failure, neurological symptoms including weakness, confusion and visual impairment, respiratory symptoms, skin lesions, chest pain, leg pain, back pain and constitutional symptoms such as anorexia, malaise and weight loss. Fungal endocarditis is fatal without treatment. It has a high morbidity and mortality, as well as a potential for relapse, so patients with uncommon non-Aspergillus mould endocarditis may require lifelong suppressive antifungal therapy.[17]