Microbiology Demystified

dery substance that is sometimes found coating fruits and leaves is a yeast.

Yeasts can also reproduce sexually.

MOLDS

When a mold forms an asexual spore, the spore will detach itself from the par-

ent and then germinate into a new mold. This process is considered reproduction

because a second new organism grows from the spore.

FUNGI CLASSIFICATION

Asexual fungal spores are formed on hyphae of fungi. When these hyphal spores

germinate, they are identical to the parent. Asexual spores reproduce by the

process of cell division. In sexual cell reproduction, the spores are produced by

the fusion of nuclei from two opposite fungi of the same species. These fungi

will have the same characteristics of both parents. Asexual spores produce more

frequently than sexual spores. Asexual spores are present in virtually every envi-

ronment on the planet.

Some fungi change their structure based on their natural habitat. This is

referred to as dimorphism, the property of having two forms of growth. For

example, some fungi appear non-filamentous when growing outside their natu-

ral habitat but filamentous when growing in their natural habitat. Such changes

of appearance can make it challenging to identify a particular type of fungus.

Fungal classification is based on the type of sexual spores they produce.

Listed are examples of the divisions of the kingdom Fungi:

• Zygomycota: Zygomycotaare conjugative fungi. They reproduce both sex-
  ually (zygospores) and asexually (sporangiospores). An example is:
  Rhizopus nigricans, a black bread mold.


• Ascomycota: Ascomycota, also called sac fungi, have sac-like cells called
  asci. These are yeasts, truffles, morels, and common molds. Fungi in
  this group reproduce sexually and asexually. Their sexual spores (conidio-
  sphores) freely detach with the slightest movement (conidia) and there-
  fore can cause infection (opportunistic disease) or an allergic reaction.
  Examples are:
  
  
  • Blastomyces: Blastomycescauses blastomycosis, which is a general pul-
    monary disease.
  
  
  • Histoplasma: Histoplasma is a fungus found in bird and bat droppings;
    it causes histoplasmosis, which is known as the fungus flu.
  
  
  
  

(^170) CHAPTER 11 The Eukar yotes