Deuteromycetes

The term Deuteromycetes originates from the Greek word “deuteros”, meaning “second,” and “mykes”, meaning “fungus.” These fungi are often called Fungi Imperfecti because their sexual stage (teleomorph) has not been observed. They reproduce only through asexual spores, mainly conidia, and therefore could not be placed accurately within the traditional fungal classification system that relies heavily on reproductive structures.

1.0General Characteristics of Deuteromycetes

Deuteromycetes display several unique features that distinguish them from other fungal groups.

1. Eukaryotic and Multicellular:
   Most Deuteromycetes are multicellular eukaryotic organisms with filamentous structures. Some, like Candida, are unicellular yeasts.
2. Mycelial Structure:
   The body of Deuteromycetes is composed of septate hyphae, forming an extensive mycelium. The septa have pores allowing cytoplasmic flow between cells.
3. Cell Wall Composition:
   The cell wall is made primarily of chitin and glucans, which provide rigidity and protection.
4. Nutrition:
   These fungi are heterotrophic, obtaining nutrients from organic materials. They can be saprophytic, parasitic, or symbiotic:
5. • Saprophytic species feed on dead and decaying matter.
   • Parasitic forms infect plants and animals.
   • Symbiotic forms coexist beneficially with plants or other organisms.
5. Reproduction:
   Only asexual reproduction is known, typically through conidia (asexual spores). No sexual reproduction or fruiting bodies have been identified.
6. Habitat:
   Deuteromycetes are found in diverse habitats such as soil, decaying wood, food products, textiles, and living tissues of plants and animals.
7. Pigmentation:
   Many species produce pigments, giving colonies characteristic colours—useful for identification.

2.0Classification of Deuteromycetes

The classification of Deuteromycetes is based mainly on morphological characteristics, particularly the type and arrangement of conidia. 

Taxonomic Position

• Kingdom: Fungi
• Division: Deuteromycota (Fungi Imperfecti)
• Class: Deuteromycetes

Common Genera

• Aspergillus
• Penicillium
• Alternaria
• Fusarium
• Colletotrichum
• Helminthosporium
• Trichophyton
• Candida

Subdivision Based on Conidial Development

1. Moniliales:
   Fungi producing single-celled or multicellular conidia, such as Aspergillus and Penicillium.
2. Melanconiales:
   Fungi forming conidia in acervuli (small, cushion-like fruiting bodies), such as Colletotrichum.
3. Sphaeropsidales:
   Fungi producing conidia inside flask-shaped structures called pycnidia, such as Phoma.

3.0Structure of Deuteromycetes

The vegetative body of Deuteromycetes is a mycelium made up of branched, septate hyphae. The mycelium spreads across the substrate, absorbing nutrients through extracellular digestion.

Hyphae and Mycelium

• Hyphae: Thread-like filaments that form the basic structural unit.
• Mycelium: A network of hyphae that anchors the fungus and facilitates nutrient absorption.

Conidiophores and Conidia

Asexual reproduction occurs through conidiophores, specialised hyphae that bear conidia.

• Conidiophores may be single or branched.
• Conidia are non-motile, thin-walled spores formed externally on the conidiophore tip.

Example:
In Aspergillus, conidiophores end in a swollen vesicle from which conidia are produced in chains, while in Penicillium, the conidia are borne in brush-like clusters.

4.0Deuteromycetes Lifecycle

The lifecycle of Deuteromycetes is relatively simple compared to other fungi, primarily because only the asexual phaseis known. Their propagation and survival depend largely on the formation and dispersal of conidia.

1. Spore Germination

The lifecycle begins when conidia fall on a suitable surface and germinate under favourable environmental conditions such as moisture, warmth, and nutrient availability. Each spore produces a germ tube, which elongates and develops into a hypha.

2. Vegetative Growth

The growing hyphae spread to form an extensive mycelial network. This stage is essential for nutrient absorption and colonization of the substrate.

3. Conidiophore Formation

After sufficient vegetative growth, certain hyphae differentiate into conidiophores, which are specialised structures for spore formation. The morphology of conidiophores varies among genera, aiding in fungal identification.

4. Conidia Formation and Dispersal

The conidia are formed either singly or in chains on the tips of conidiophores. Once mature, they detach and are dispersed by air, water, insects, or mechanical disturbance. These spores germinate again to continue the cycle.

Since no sexual reproduction has been observed, the lifecycle remains asexual and continuous, allowing rapid colonisation and survival in changing environments.

5.0Reproduction of Deuteromycetes

Asexual Reproduction

Asexual reproduction occurs through:

1. Conidia: Formed externally on conidiophores; the most common mode of reproduction.
2. Oidia: Hyphal fragments that act as spores.
3. Chlamydospores: Thick-walled resting spores formed during unfavourable conditions.
4. Sclerotia: Hard, compact masses of mycelium serving as perennating structures.

6.0Economic and Ecological Importance of Deuteromycetes

Despite lacking a sexual stage, Deuteromycetes have tremendous ecological and economic significance.

1. Beneficial Roles

• Antibiotic Production:
  Penicillium notatum and Penicillium chrysogenum produce penicillin, the first and most famous antibiotic.
• Industrial Applications:
  Aspergillus niger is used for the production of citric acid, enzymes, and organic acids.
  Penicillium species are used in cheese manufacturing.
• Biological Control:
  Certain species, such as Trichoderma, act as biocontrol agents against plant pathogens.
• Decomposition:
  Saprophytic Deuteromycetes decompose organic matter, recycling nutrients back into the ecosystem.

2. Harmful Effects

• Plant Diseases:
  Fusarium, Alternaria, and Colletotrichum species cause major crop losses.
• Human and Animal Diseases:
  Trichophyton causes skin infections, while Candida causes fungal infections in humans.
• Food Spoilage:
  Many Deuteromycetes grow on stored grains, bread, and fruits, leading to deterioration and wastage.

7.0Deuteromycetes Examples

• Alternaria solani: Early blight of Potato
• Colletotrichum falcatum Red rot of sugarcane
• Trichoderma: It produces "Ringworm" in humans