Microbiology Lab Report — Identification of Fungi Essay Example

  • Category:
    Biology
  • Document type:
    Assignment
  • Level:
    Undergraduate
  • Page:
    2
  • Words:
    1195

Aims:

  1. To examine cultures of common moulds — Mucor, Aspergillus, and Penicillium, so as to determine their growth characteristics.

  2. To inoculate Sabaroud’s agar with Mucor heimalis (+) and (-), strains to demonstrate the development of zygospores (sexual reproduction).

  3. To prepare slide cultures of moulds for detailed microscopic examination of these organisms.

Background Information

Fungi are more complex organisms than bacteria. They often grow as multicellular bodies rather than single celled forms. The multicellular bodies consist of long threads or filaments of elongated cells called vegetative hyphae, and fruiting bodies — sexual reproductive structures, that form on fertile hyphae, which arise in turn from the vegetative hyphae or mycelia. Some of the popularly known are fleshy fungi, yeasts and moulds. Yeasts are normally organisms that are unicellular, but some can form hyphae under the right conditions. Moulds are organisms that have filaments like smuts, rust and mildew. Examples of fleshy fungi are puffballs, mushrooms, toadstools and bracket fungi. In this exercise study will be made of some of the characteristics of the group of fungi known as moulds.

When moulds are to be studied, the vegetative hyphae can easily be seen by examining a petri dish under low power magnification through the bottom of the plate, since the filaments grow out along the surface of the medium, drawing in nutrition for the mould organism. By turning the plate over, removing the lid and examining the surface growth, the fertile hyphae and their fruiting bodies can be observed quite easily.

The common moulds may be divided into two BASIC groups. In the first group are the moulds that develop as cottony, coarse masses of growth, often dirty grey or black. They produce nonsexual spores inside a closed spore case called a sporangium. The spores are termed sporangiospores. Sexual reproduction in this group results in a large thick walled spore, a zygospore. The vegetative hyphae have few or no cross-walls or septae and may be referred to as nonseptate.
Mucor and Rhizopus (black bread mould) are common members of this group and are known as Zygomycetes.

In the second group are the moulds that basically appear as powdery masses of growth, — blue, green, yellow, drab olive, or brown to black. The blue moulds found on oranges or on Roquefort or blue cheese are common examples. The hyphae, both vegetative and fertile, are divided by cross walls into a series of elongated boxes. These cross walls (septa) help to identify this group of organisms. Sexual spores produced by these moulds are borne naked (not enclosed in a spore case) on fertile hyphae. These asexual spores produced at the end of a conidiophore are called conodiospores. Sexual reproduction results in four to eight ascospores formed within a sac like structure — an ascus. Penicillium and Aspergillus are common Genera within this group, which are classed as Ascomycetes (higher fungi).

CLASSIFICATION OF FUNGI

Zygomycota

  • Have coenocytic hyphae.

  • Produce asexual spores — sporangiospores

  • Produce sexual spores – zygospores

  • Examples : Rhizopus, Mucor

Ascomycota (sac fungi)

  • Produce asexual spores, usually conidiospores.

  • Ascospores result from fusion of 2 nuclei morphologically similar or dissimilar. These spores are produced in an ascus.

  • Septate hyphae

  • Examples: Dutch elm disease, truffles, red, brown and blue green moulds which cause food spoilage.

Basidiomycota (club fungi)

  • Have septate hyphae

  • This division includes fungi, which produce mushrooms.

  • Produce basidiospores on a pedestal called a basidium.

  • Some produce asexual conidiospores.

Deuteromycota (Fungi Imperfecti)

Until recently fungi whose sexual cycle had never been observed were classified as Deuteromycota. Scientists are now able to use genetic sequencing to classify these organisms and most of them have been found to belong to the Ascomycota or the Basidiomycota.

Growth Characteristics of Common Moulds

This
genus consists of thousands of subdivisions of fungi. Many of these include moulds. Therefore, many of the characteristics that you would notice with moulds would usually be prominent in the mucor genus. Here are a few of the main characteristics of this genus: they usually have a gray coloring, they grow extremely fast when in right conditions, in culture, mucor tends to grow upwards instead of outwards, and finally, they reproduce asexually by means of spores.

Aspergillus

Fungi procreate by developing very small spores which can without difficulty be carried through the air. They have a conidial top or body that yields spores. They grow properly under a multiplicity of conditions and most of them are plant pathogens.

Penicillium

During its growth, penicillium produces Microbial volatile organic compounds (MVOCs). Penicillium commune generates 2-methyl-isoborneol, a very strong musty smell. This subdivision of fungi in general has a fast rate of growth. Its colonies normally are blue-green, green, or grey green. They can as well be pinkish, white or yellow. In most cases, the texture of the colonies is velvety and in other cases powdery.

Development of Zygospores

Zygospores are produced where two mycelia of different sexual types meet and usually require incubating the culture for some three days. After five days of incubation a dark line of mature zygospores can readily be seen at the interface.

Zygospores are formed with continuous natural or artificial light after a dark period. When strains are mated near one another and far apart in the same plates, zygospores typically form in the close matings but rarely in the far matings even though the colonies grow together. Different wavelengths of light have little effect on zygospore formation.

Describing the Images

Microbiology Lab Report - Identification of Fungi

Aspergillus

has a flowerly appearance that sheds off filaments of beads. These string-like beads are called spores. They appear to be spherical in shape, viewed singly under a light microscope.AspergillusWhen observed under a light microscope,

Penicillium

have a brush-like appearance. At the end of these brushes, there are with strings of beads that spring out.PenicilliumWhen viewed under a light microscope, the spores from this genus also look spherical in shape. In order to differentiate between the spores of penicillium and those of aspergillus, one needs to keenly look at the growth structure that produces them (the spores). The growth structures of

Microbiology Lab Report - Identification of Fungi 1

Mucor (Sporangiosphore)

In some parts of the spores, flagellum was not were never seen. Formation of sporangial structures was followed by examination of parts of sporangia at different stages of growth. The sporangial covering was the progression of the outermost sheath of the sporangial structures known as sporangiophores. They are formed when the hyphae that are enveloped within sporangial walls divide. These spores were formed perhaps by the division of the hyphae simultaneously. An intersporal substance, that appeared to come from the outer part of the sheath of sporangial hyphae, is visible.

Mucor (Zygosphores)

Microscopic examination of mucor showed a widespread conflagration, granulomas with eosinophils as well as many fungal hyphae. Zygospores are seen engulfed by eosinophilic substance. This phenomenon is called the Splendore-Hoeppli.

List of References

Diseases and disorders. (2008). Tarrytown, N.Y: Marshall Cavendish.

Metsäntutkimuslaitos., & Hintikka, V. (1960). The role of soil fungi in the formaiton of different humus types: Especially in raw humus formation in northern forest. Helsinki: Finnish Forest Research Institute.

Rogers, K. (2011). Fungi, algae, and protists. New York, NY: Britannica Educational Pub. in association with Rosen Educational Services.

Burnett, J. (2003). Fungal populations and species. Oxford [u.a.: Oxford Univ. Press.