Ascomycete

Ascomycete

Ascomycetes, also known as sac fungi, are a division of the kingdom Fungi that, together with the Basidiomycota, form the subkingdom Dikarya. They are characterized by the formation of spores, called ascospores, in a special type of microscopic cell called an ascus. Ascomycetes are the largest phylum of fungi, with over 64,000 species.

Characteristics

Ascomycetes are defined by their production of ascospores in asci. The asci are typically contained in a fruiting body called an ascocarp or ascoma. The ascocarp can take various forms, such as:

• Apothecium: a cup-shaped structure
• Perithecium: a flask-shaped structure
• Cleistothecium: a closed, spherical structure

The life cycle of ascomycetes includes both sexual and asexual reproduction. During sexual reproduction, two compatible hyphae fuse, leading to the formation of an ascus where meiosis occurs, producing haploid ascospores. Asexual reproduction often involves the production of conidia, which are asexual spores formed at the tips of specialized hyphae called conidiophores.

Ecology and Importance

Ascomycetes play crucial roles in various ecosystems. They are decomposers, breaking down complex organic materials, and are also important in nutrient cycling. Some ascomycetes form mutualistic relationships with plants, such as mycorrhizal associations, or with algae and cyanobacteria, forming lichens.

Ascomycetes are also significant in human affairs. They include species that are used in the production of antibiotics, such as Penicillium species, and in the fermentation of food and beverages, such as Saccharomyces cerevisiae, the yeast used in baking and brewing. However, some ascomycetes are pathogens of plants and animals, including humans. For example, Aspergillus species can cause respiratory infections, and Candida albicans is a common cause of yeast infections.

Classification

The phylum Ascomycota is divided into three subphyla:

• Pezizomycotina: This is the largest subphylum and includes most of the filamentous ascomycetes.
• Saccharomycotina: This subphylum includes the true yeasts, such as Saccharomyces cerevisiae.
• Taphrinomycotina: This subphylum includes a variety of fungi with diverse lifestyles, including some plant pathogens.

Notable Genera and Species

• Aspergillus - A genus of molds known for their role in food spoilage and production of aflatoxins.
• Penicillium - Known for the production of the antibiotic penicillin.
• Saccharomyces cerevisiae - Baker's yeast, used in baking and brewing.
• Neurospora crassa - A model organism in genetics and molecular biology.
• Candida albicans - A yeast that can cause infections in humans.

Research and Applications

Ascomycetes are extensively studied for their genetic and biochemical properties. They serve as model organisms in research, particularly Neurospora crassa and Saccharomyces cerevisiae. The study of ascomycetes has led to advances in understanding fungal genetics, cell biology, and the development of antifungal drugs.

References

• Alexopoulos, C. J., Mims, C. W., & Blackwell, M. (1996). Introductory Mycology. John Wiley & Sons.
• Deacon, J. W. (2006). Fungal Biology. Blackwell Publishing.

External Links

• Mycology Online
• Fungi Perfecti