Introductory Microbiology

Groups of microorganisms

• The major groups of protists are briefly described below. Although viruses are not protists or unicellular organisms, they are included for two reasons:

  a) The techniques used to study viruses are microbiological in nature and
  b) Viruses are causative agents of diseases, hence, diagnostic procedures for their identification are employed in the clinical microbiological laboratory as well as the plant pathology laboratory.

Algae:
Algae are relatively simple organisms. The most primitive types are unicellular. Others are aggregations of similar cells with little or no differentiation in structure or function. Still other algae, such as the large brown kelp, have a complex structure with cell types, specialiged for particular functions. Regardless of size or complexity, algal cells contains chlorophyll and are capable of photosynthesis. Algae are found most commonly in aquatic environments or in damp soil.

Viruses:
Viruses are very small non-cellular pasasites or pathogens of plants, animals and bacteria as well as other protists. They are so small that they can be visualized only by the electron microscope. Viruses can be cultivated only in living cells.

Bacteria:
Bacteria are unicellular prokaryotic organisms or simple associations of similar cells. Cell multiplication is usually by binary fission.

Protozoa:
Protozoa are unicellular eukaryotic organisms. They are differentiated on the basis of morphological, nutritional and physiological characteristics. Their role in nature is varied but the best known protozoa are the few that cause disease in human beings and animals.

Fungi:
Fungi are eukaryotic lower plants devoid of chlorophyll. They are usually multicellular but are not differentiated into roots, stems and leaves. They range in size and shape from single celled microscopic yeasts to giant multicellular mushrooms and puffballs. We are particularly interested in those organisms commonly called molds, the mildews, the yeasts and the plant pathogens known as rusts. True fungi are composed of filaments and masses of cells which make up the body of the organism known as mycelium. Fungi reproduce by fission by budding or by means of spores borne on fruiting structures that are quite distinctive for certain species.

• Microbiologists may specialize in the study of certain groups of microorganisms. Strictly speaking, bacteriology is the study of bacteria, but the term is often used as a synonym for microbiology, Protozoology is the study of protozoa; a special branch of Protozoology called parasitology deals exclusively with the parasitic or disease producing protozoa and other parasitic micro and macroorganisms.
• Mycology is the study of fungi such as yeasts and molds. Virology is the science that deals with viruses. Phycology is the study of algae. Further specialization in some aspect of the biology of a particular group of organisms is not uncommon.e.g., Bacterial genetics, algal physiology and bacterial cytology.

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