Collection Of Hyphae Growing In One Place Is Called

The term fungi describes a taxonomic classification of organisms but no longer includes organisms such as slime molds and water molds that had traditionally been considered to be fungi (figure 12.11). The slime molds and water molds once thought to be related to the fungi now appear to have evolved much earlier and will be considered separately in this chapter.

Fungi require organic compounds for energy and as a carbon source, often from dead organisms. Most fungi are aerobic or facultatively anaerobic. Only a few fungi are anaerobic. ■ aerobic, p. 88 ■ facultatively anaerobic, p. 89 ■ anaerobic, p. 88

A large number of fungi cause disease in plants. Fortunately, only a few species cause disease in animals and humans. As modern medicine has advanced to treat once-fatal diseases, however, it has left many individuals with impaired immune systems. It is these immunocompromised individuals who are most vulnerable to the fungal diseases.

Animals

Choanoflagellates i-Fungi-

- Zygomycetes -Ascomycetes

— Basidiomycetes -Chytridiomycetes

Land plants

Chlorophytes (green algae) ■ Cryptomonads

Rhodophyta (red algae)

Stramenophiles

Chrysophyta (golden brown algae and diatoms) - Phaeophyta (brown algae) . Oomycetes (water molds)

Ciliates

■ Pyrrophyta - dinoflagellates Apicomplexans

Cellular slime molds Acellular slime molds Entamoebids Amoeboflagellates Kinetoplastids

Euglenoids

Parabasalians

Diplomonads

Microsporans

Bacteria

Figure 12.11 A Phyiogenetic Scheme of Eukaryotes Based on rRNA Sequence Comparisons The fungal groups are highlighted in yellow.

Chapter 12 The Eukaryotic Members of the Microbial World

Figure 12.12 Fungi Range in Size from Microscopic to Macroscopic Forms (a) Microscopic Candida albicans, showing the chlamydospores (large, round circles) that are an asexual reproductive spore. (b) Polyporussulphureus (chicken of the woods), a shelflike fungus growing on a tree. (c) Amanita muscaria, a highly poisonous mushroom, growing in a cranberry bog on the Oregon coast.

Figure 12.12 Fungi Range in Size from Microscopic to Macroscopic Forms (a) Microscopic Candida albicans, showing the chlamydospores (large, round circles) that are an asexual reproductive spore. (b) Polyporussulphureus (chicken of the woods), a shelflike fungus growing on a tree. (c) Amanita muscaria, a highly poisonous mushroom, growing in a cranberry bog on the Oregon coast.

The study of fungi is known as mycology, and a person who studies fungi is known as a mycologist. Along with bacteria, fungi are the principal decomposers of carbon compounds on earth. This decomposition releases carbon dioxide into the atmosphere and nitrogen compounds into the soil, which are then taken up by plants and converted into organic compounds. Without this breakdown of organic material, the world would quickly be overrun with organic waste.

Classification of Fungi

Many fungi are microscopic and can be examined using basic microbiological techniques; others are macroscopic (figure 12.12). All fungi have chitin in their cell walls and no flagellated cells at any time during their life cycle. There are four groups of true fungi, the Zygomycetes, Basidiomycetes, Ascomycetes, and Deuteromycetes or Fungi Imperfecti. The classification of the first three groups is based on their method of sexual reproduction. For the fourth group, the Deuteromycetes, sexual reproduction has not been observed, and so these fungi have traditionally been lumped together. With additional rRNA analysis, however, most Deuteromycetes can now be placed in one of the other three fungal groups. Most are either Ascomycetes or Basidiomycetes who have lost the sexual part of their life cycle (table 12.3).

The Zygomycetes include the common bread mold (.Rhizopus) and other food spoilage organisms. The Ascomycetes include fungi that cause Dutch elm disease and rye smut. Smuts

Table 12.3 Characteristics of Major Groups of Fungi

Group and

Representative

Member

Usual Habitat

Some Distinguishing Characteristics

Asexual Reproduction

Sexual Reproduction

Zygomycetes Rhizopus stolonifer (black bread mold)

Terrestrial

Multicellular, coenocytic mycelia (with many haploid nuclei)

Asexual spores develop in sporangia on the tips of aerial hyphae

Sexual spores known as zygospores can remain dormant in adverse environment

Basidiomycetes Agaricus campestris

(meadow mushroom) Filobasidiella neoformans

Terrestrial

Multicellular, uninucleated mycelia. Group includes mushrooms, smuts, rusts that affect the food supply

Commonly absent

Produce basidiophores that are borne on club-shaped structures at the tips of the hyphae

Ascomycetes Neurospora, Saccharomyces cerevisiae (baker's yeast)

Terrestrial, on fruit and other organic materials

Unicellular and multicellular with septated mycelia

Is common by budding; conidiospores

Involves the formation of an ascus (sac) on specialized hyphae

Deuteromycetes (Fungi Imperfecti) Penicillium, Aspergillus

Terrestrial

A number of these are human pathogens

Budding

Absent or unknown

Nester-Anderson-Roberts: I II. The Microbial World I 12. The Eukaryotic I I © The McGraw-Hill

Microbiology, A Human Members of the Microbial Companies, 2003

Perspective, Fourth Edition World

Cell wall

Mitochondria

Figure 12.13 Morphology of a Yeast Cell As Seen with an Electron Microscope

Cell wall

Mitochondria

Figure 12.13 Morphology of a Yeast Cell As Seen with an Electron Microscope got this common name because the black spores that are produced give the appearance of soot. The Basidiomycetes include the common mushrooms and puffballs. Many medically and economically important species of fungus, including the one that produces penicillin, belong to the Deuteromycetes. In addition to these four groups of fungi, the Chytridiomycetes are a close relative on the evolutionary scale. They have flagellated sexual spores and more variable life cycles, however, than the fungi. Most of these organisms live in water or soil, and a few are parasitic. Black wart disease of potatoes is caused by a chytridiomycete.

Common Groupings of Fungal Forms

When people talk about fungi, they frequently use terms such as yeast, mold, and mushroom. These terms have nothing to do with the classification of fungi but instead indicate their morphological forms.

Yeasts are single-celled fungi (figure 12.13). Yeasts can be spherical, oval, or cylindrical and are usually 3 to 5 mm in diameter. Some yeasts reproduce by binary fission, whereas others reproduce by budding, in which a small outgrowth on the cell produces a new cell (figure 12.14).

Molds are filamentous fungi. A single filament is known as a hypha (plural, hyphae), and a collection of hyphae growing in one place is known as a mycelium. Hyphae develop from fungal spores. A fungal reproductive spore is typically a single

Step 1

Nucleus

Step 2

-Bud

Step 2

-Bud

Figure 12.14 Budding in Yeast (1) Cell wall softens at point A, allowing the cytoplasm to bulge out. (2, 3) Nucleus divides by mitosis, and (4) one of the nuclei migrates into the bud. (5) Cell wall grows together and the bud breaks off, forming a new cell.

cell about 3 to 30 mm in diameter, depending on the species. When a fungal spore lands on a suitable substrate, it germinates and sends out a projection called a germ tube (figure 12.15). This tube grows at the tip and develops into a hypha. The cells divide and form new cells. In some fungi, the cell wall does not completely close off one cell from another. In that case the cells become multinucleated. The white mass seen inside the potato or on moldy bread (figure 12.16) is an example of a mycelium. Only a small portion of the mycelium is actually visible on the

Figure 12.15 Formation of Hyphae and Mycelium Spores of fungi germinate to form a projection from the side of the cell called a germ tube, which elongates to form hyphae. As the hyphae continue to grow, they form a tangled mass called a mycelium.

Mycelium

Germ tube

Mycelium

Germ tube

Figure 12.15 Formation of Hyphae and Mycelium Spores of fungi germinate to form a projection from the side of the cell called a germ tube, which elongates to form hyphae. As the hyphae continue to grow, they form a tangled mass called a mycelium.

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Responses

  • bob
    What is the collection of hyphae?
    2 years ago
  • oskar
    How to collect hayphae ?
    12 days ago

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