Conidia

As conidia, (Greek konia = dust), are characteristic, asexually (vegetatively) formed forms of propagation (secondary fruit forms) which often only develop under very specific cultivation conditions. Conidia are formed by many skin fungi (dermatophytes). Form and type of conidia formation serve as differentiation characteristics for fungal identification.

In the medical mycology (this concerns above all the Fungi imperfecti) one distinguishes:

• unicellular microconidia
• and
• multicellular macroconidia.

The formation of these fructification organs (conidiogenesis) varies according to the fungal species. It is sometimes so characteristic that it can be used as a species identification. Conidia can be formed by sprouting (blastokonidia) or by fragmentation of hyphae (arthrokonidia).

The following types of conidia can be distinguished:

• Aleurispores are formed from the inflated end of a hyphe or a lateral inflation and are separated by septa.
• Arthroconidia are formed by dividing existing hyphae by septa and then transforming the individual segments into spores.
• Blastoconidia are formed by budding at hyphal tips or other positions and mature from the base. They separate without the formation of septa (e.g. Cladosporium)
• Phialaconidia are secreted by cells, the phialids, which are formed at the end of the hyphae (e.g. Penicillium).
• Chlamydospores are the thick-walled permanent spores, which are formed intercalary (restricted to certain zones) or by swelling of hyphal ends.
• Cystoconidia form within a sac-like structure that develops at the end of a hyphe (e.g. Mucor)
• Arthroconidia form within a hyphema, whereby a whole cell in the association transforms into a conidia (e.g. Geotrichum = milk mould)

Asexual, vegetative or asexual reproduction is common among fungi. Fungi that reproduce exclusively asexually are called fungi imperfecti. The dermatophytes, the molds as well as several plant-damaging types belong to it.

During sexual reproduction, the fungi first form gametes. These are formed by reduction or maturation division (meiosis) and contain a simple (haploid) set of chromosomes. When two gametes merge, a cell with a double (diploid) set of chromosomes is formed again. This is called a zygote or sexual spore. During sexual reproduction, a new combination of the parental genetic material occurs.

1. Court H (2019) in: H. Hof (Editor) Medical Microbiology. Thieme Publishing House Stuttgart S. 478-479