The Role of Pyrenomycetous Fungi in Environmental Ecology – A Review

Pyrenomycetes are fungi that mainly grow as tiny, flask-shaped fruiting bodies called perithecia that contain asci and ascospores. We can find them on a variety of surfaces like soil, animal waste, decaying leaves, wood, and even other fungi. These "little black dots" makeup the largest group of fungi in the Ascomycota phylum. Pyrenomycetes are both ecologically and economically important because they include fungi which are often used in research, as well as harmful pathogens that cause diseases like chestnut blight, Dutch elm disease, and beech bark disease. These fungi are found allover the world indifferent ecosystems and geographical areas primarily as saprobes, playing a key role in breaking down organic matter and recycling nutrients. Most of them are hard to spot without a keen eye since their fruiting bodies are usually small (less than 1 mm in diameter) and dark-coloured, often blending into the surface of plant material, both living and dead. Many Pyrenomycetes also have a stroma, a much larger structure embedding the perithecia in fungal tissue. In narrow sense Pyrenomycetes encompass the class Sordariomycetes, but some species of Dothideomycetes, Eurotiomycetes and Lecanoromycetes with superficially similar fruiting bodies. The terms “Pyrenomycetes” is no longer used in a taxonomic sense and have been replaced by the terms Sordariomycetes, to refer to one major Class of fungi in the Phylum Ascomycota. In this paper the term “pyrenomycetes” is used in a general sense to refer to the fungi that occur in the class Sordariomycetes. Fungi are the principal decomposers in terrestrial ecosystems and one of the most important ecological roles of fungi, is there function as decomposer also known as saprophyte. Fungi breakdown Complex organic matters such as dead plants, animals and other organic materials, into simpler compounds. This decomposition process is vital for nutrient cycling in ecosystems. Without this, organic materials would accumulate and essential nutrients like carbon, nitrogen and phosphorus would become trapped, preventing their return to the soil and the food chain. fungi secrete enzymes that breakdown tough substances such as cellulose, Lignin and chitin which most other organisms cannot degrade efficiently. Pyrenomycetous fungi not only decompose organic matters but also play an important role in plastic biodegradation. The main classes of enzymes involved in plastic biodegradation are hydrolases and oxidoreductases. These enzymes have been extensively studied due to their involvement both in natural and industrial processes. For example, in nature and industry they are essential in lignocellulose biodegradation , fungal pathogenesis and the hydrolysis of triacylglycerol to fatty acids. These enzymes also have applications in the food and textile industries and in bioremediation processes. 1.1 Systematic Position of Pyrenomycetes: Pyrenomycetes (Sordariomycetes of Eriksson and Winka 1998) is a class name formerly used to refer to a group of species with a particular shared morphology. It now is used to designate a clade that includes the orders Diaporthales, Halosphaeriales, Hypocreales, Lulworthiales, Microascales, Ophiostomatales, Phyllachorales, Sordariales and Xylariales [25]. Although the taxa in the clade encompass a wide range of macromorphologies and micromorphologies, the vast majority have a flask-shaped ascomata or perithecia. The Pyrenomycetes clade also includes numerous lineages of cleistothecial fungi, which represent multiple and repeated losses of the perithecial neck and ostiole [25]. Although almost all perithecial ascomycetes are included in the pyrenomycetes clade, there are a few exceptions. Pyxidiophora species and the Laboulbeniales are arthropod-associated ascomycetes comprising a separate clade based on SSU rDNA analyses .

In traditional taxonomy ascomycetes were classified according to their ascoma-types, with the class Pyrenomycetes including all taxa having perithecia. Later, the development of ascomata and the type of ascus were employed for higher-level classification, and consequently, Loculoascomycetes was separated from Pyrenomycetes[7,9,13]. However, molecular studies show that even these revised classifications were too coarse. The Loculoascomycetes fall into two distinct and not closely related groups, which are placed in two clades: Chaetothyriomycetidae and Dothideomycetes[14,16]. Ascospore morphology has been widely used in taxonomy of ascomycetes, and Sordariales is a prominent example of this. Molecular data suggest that ascomatal wall morphology is abetter predictor of phylogenetic relationships in these fungi. Further, the molecular data helped to redefine the circumscription of Sordariales. The majority of non-lichenized pyrenomycetes form a monophyletic group: Sordariomycetes. However, the lichenized pyrenomycetes are highly polyphyletic.

Pyrenocarpous lichen-forming fungi occur in several lineages each in Dothideomycetes, Chaetothyriomycetidae and Lecanoromycetes, whereas no lichenized forms are currently known in the classical Sordariomycetes [27]. Sordariomycetes are also known as Pyrenomycetes, from the Greek πυρἠν - 'the stone of a fruit' - because of the usually somewhat tough texture of their tissue [5].