Geoscience Reference
In-Depth Information
Bacteria are unicellular structures, a few microns in length and enclosed in a
membrane or cell wall. They exist in a variety of shapes and sizes: a bacterium or a
bacillus is a straight rod; a vibrio is a curved rod ( Fig. 43 ) ; a coccus is a spherical cell.
The cell content, the protoplasm, performs many functions and activities which in
multicellular animals (metazoa), mammals for example, are carried out in specialized
tissues or organs. A whole series of enzymes is contained within the bacterial cell.
Enzymes operate in all the different biochemical activities of metabolism, digestion,
respiration, excretion and growth. There is nuclear material, i.e. nucleic acids, but no
organized cell nucleus. Nucleic acids are involved in the genetic processes of the cell
and its reproduction. Bacteria multiply by simple fission; the cell grows, elongates
and then divides into two. Under favourable conditions some species can divide with-
in about twenty or thirty minutes. Weight for weight, bacterial tissue is metabolic-
ally much more active than that of higher animals, possibly because all the different
activities are performed in the single cell. Moreover, because of the existence of the
vast number of microbial species, it is not surprising that microorganisms as a whole
are capable of a great range of biochemical activities. The current edition of Bergey's
Manual of Determinative Bacteriology (1984) lists thousands of bacterial species, re-
flecting their astonishing diversity in form, nutritive and physiological capacities and
ecological characteristics.
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