Ulocladium botrytis is an anamorphic filamentous fungus belonging to the phylum Ascomycota. Commonly found in soil and damp indoor environments, U.botrytis is a hyphomycetous mould found in many regions of the world. It is also occasionally misidentified as a species of the genera Alternaria or Pithomyces due to morphological similarities. Ulocladium botrytis is rarely pathogenic to humans but is associated with human allergic responses and is used in allergy tests. Ulocladium botrytis has been implicated in some cases of human fungal nail infection. The fungus was first discovered in 1851 by German mycologist Carl Gottlieb Traugott Preuss.
History and taxonomy The genus Ulocladium was first discovered in 1851 by German mycologist, Preuss, in a small batch of his specimens. 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. This sample was later acquired by the Botanisches Museum in Berlin. At the time, the name of the genus and the species type was published as a nomen nudum due to insufficient description. Furthermore, certain taxa of Ulocladium greatly resemble Alternaria species, resulting in occasional misidentifications. 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. After much study, it was found that Alternaria maritima was in fact Ulocladium botrytis. Although Ulocladium is now a genus of its own, it was once included in the genus Alternaria. 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. Some modern sources believe that Ulocladium botrytis should be considered conspecific with Ulocladium atrum.
Growth and morphology Ulocladium botrytis is a hyphomycetous mould that favors growth in damp indoor environments. Although it mainly uses nitrogen, other nutrient sources have been tested to determine that U. botrytis growth rate is dependent on the type of media provided. Ulocladium botrytis colonies are commonly velvety in texture and grow in an assortment of colors ranging from dark blackish brown to black. The hyphae are 3-4 μm in diameter and yellow to golden brown in colour with a smooth or slightly rough texture. Conidiophores are short and either erect and ascending, or contorted into various shapes. In addition, they are often bifurcated near the apex at sharp angles. 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. The conidia themselves are typically ellipsoidal or obovoid in shape; spheroidal conidia are uncommon in this species. They are golden brown in color and frequently have a minute hilum and a warty, verrucose exterior ornamentation. Ulocladium botrytis conidia typically have three transverse septa and longitudinal septum, but these septa rarely overlap to form a cross. This species never forms conidial chains and the conidia never have a beak.
Physiology Ulocladium botrytis is an anamorphic fungus, thus it undergoes asexual reproduction. 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. 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. 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. 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. In contrast, its ability to hydrolyze liquid cellulose under alkaline conditions is best at a pH of 8.0. Additionally, a new tyrosine kinase (p56tck) inhibitor called ulocladol, with the molecular formula C16H14O7, was found in ethyl acetate extract from U. botrytis. Ulocladium botrytis also synthesizes extracellular keratinases and can grow in the presence of keratin. Moreover, this fungus can produce carboxymethyl cellulase and protease on Eichhornia crassipes wastes. 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. Furthermore, U. botrytis aids in decreasing aldehyde levels. Dodecane and 9,10,12,13-tetrahydroxyheneicosanoic acid were also found as metabolites of U. botrytis. Another U. botrytis metabolite is 1-hydroxy-6-methyl-8-(hydroxymethyl)xanthone, which has antimicrobial effects indicating its identification as an antifungal metabolite. Importantly, a major protein allergen of Alternaria alternata, termed Alt a 1, and an allergen homologous to it is expressed in the excretory-secretory materials of U. botrytis.
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