Ulocladium botrytis

The genus Ulocladium was first discovered in 1851 by German mycologist, Preuss, in a small batch of his specimens.^[7] An abundant hyphomycetous growth of Ulocladium was found on a thin sliver of wood and was drawn and labeled by Preuss as Ulocladium botrytis in his manuscript.^[7] This sample was later acquired by the Botanisches Museum in Berlin.^[7] At the time, the name of the genus and the species type was published as a nomen nudum due to insufficient description.^[7] Furthermore, certain taxa of Ulocladium greatly resemble Alternaria species, resulting in occasional misidentifications.^[4] During the late 1900s, a mycologist named Curran described Alternaria maritima as a species new to Ireland. However, Curran's new claim was questioned when another mycologist, Kohlmeyer, initiated a movement to verify the classification of this fungus.^[8] After much study, it was found that Alternaria maritima was in fact Ulocladium botrytis.^[8] Although Ulocladium is now a genus of its own, it was once included in the genus Alternaria.^[9] Several recent DNA-based phylogenetic studies have presented convincing data which places Ulocladium species within the genus Alternaria; however, Ulocladium species do not produce certain compounds and metabolites produced by Alternaria species.^[9] Some modern sources believe that Ulocladium botrytis should be considered conspecific with Ulocladium atrum.^[10]

Ulocladium botrytis is a hyphomycetous mould that favors growth in damp indoor environments.^[2] Although it mainly uses nitrogen,^[11][12] other nutrient sources have been tested to determine that U. botrytis growth rate is dependent on the type of media provided.^[13][12] Ulocladium botrytis colonies are commonly velvety in texture and grow in an assortment of colors ranging from dark blackish brown to black.^[3] The hyphae are 3-4 μm in diameter and yellow to golden brown in colour with a smooth or slightly rough texture.^[7] Conidiophores are short and either erect and ascending, or contorted into various shapes.^[7] In addition, they are often bifurcated near the apex at sharp angles.^[3] Ulocladium botrytis conidiophores are typically light golden brown in color and smooth, with a length of up to 100 μm and a thickness of around 3-5 μm.^[3] The conidia themselves are typically ellipsoidal or obovoid in shape; spheroidal conidia are uncommon in this species.^[7] They are golden brown in color and frequently have a minute hilum and a warty, verrucose exterior ornamentation.^[3] Ulocladium botrytis conidia typically have three transverse septa and longitudinal septum, but these septa rarely overlap to form a cross.^[3] This species never forms conidial chains and the conidia never have a beak.^[4]

Ulocladium botrytis is an anamorphic fungus, thus it undergoes asexual reproduction.^[1] Although it is an asexual fungus, U. botrytis possesses the mating type locus, which consists of two dissimilar DNA sequences termed MAT1-1-1 and MAT1-2-1. These U. botrytis MAT genes are essential for controlling colony size and asexual traits such as conidial size and number in U.botrytis.^[1] The U. botrytis MAT genes have lost the ability to regulate sexual reproduction in U. botrytis; however, they have the ability to partially induce sexual reproduction in Cochliobolus heterostrophus, a heterothallic species, upon heterologous complementation.^[1]

Ulocladium botrytis has cellulolytic ability and contains a cellulose-degrading enzyme complex that can degrade recalcitrant plant litter under alkaline conditions, a trait that is uncommon in other cellulolytic systems.^[12] This fungus' ability to hydrolyze cellulose in the solid form is best at a pH of 6.0, as this pH allows maximal growth of U. botrytis under alkaline conditions.^[12] In contrast, its ability to hydrolyze liquid cellulose under alkaline conditions is best at a pH of 8.0.^[12] Additionally, a new tyrosine kinase (p56^tck) inhibitor called ulocladol, with the molecular formula C₁₆H₁₄O₇, was found in ethyl acetate extract from U. botrytis.^[13] Ulocladium botrytis also synthesizes extracellular keratinases and can grow in the presence of keratin.^[14] Moreover, this fungus can produce carboxymethyl cellulase and protease on Eichhornia crassipes wastes.^[11]

As a fungus, Ulocladium botrytis produces a diverse collection of chemical compounds and metabolites. It produces mixtures of volatile organic compounds that include terpenes, alcohols, ketones, and nitrogen-containing compounds.^[2] Furthermore, U. botrytis aids in decreasing aldehyde levels.^[2] Dodecane and 9,10,12,13-tetrahydroxyheneicosanoic acid were also found as metabolites of U. botrytis.^[15] Another U. botrytis metabolite is 1-hydroxy-6-methyl-8-(hydroxymethyl)xanthone, which has antimicrobial effects indicating its identification as an antifungal metabolite.^[13] Importantly, a major protein allergen of Alternaria alternata,^[16] termed Alt a 1, and an allergen homologous to it is expressed in the excretory-secretory materials of U. botrytis.^[17][6]