Geoscience Reference
In-Depth Information
nutrient occurs forming carbon dioxide and water, and some incompletely oxidized
substances remain in the form of intermediate oxidation products, such as alcohol and
simple organic acids. The amount of energy thus mobilized is less than that theoretic-
ally possible, and therefore these anaerobic processes are distinctly less efficient than
those in aerobic metabolism.
F
IG. 44
Electron microscope photograph of cells of a
Nitrosospira
species, a nitrifying bacterium isolated from an
acid woodland soil - Geescroft Wilderness, Rothamsted Experimental Station. Note the long coiled spring
appearance. (Photograph N. W., magnification ca. 40,000.)
Temperature is also an important physical factor affecting the rate of microbial
multiplication; different microbial species have different optimal growth temperat-
ures. Some bacteria and a few fungi can grow at or near to freezing point and even ex-
hibit their optimum growth at between 5° and 10°C; such species are termed psychro-
philic and many of them are found in the sea. However, most bacterial species grow
and flourish best at between 20° and 35°C and they are described as mesophilic or-
ganisms. Some microbes show optimum growth at between 45° and 50°C and there
are other very specialized organisms which can grow even at 75° or 80°C. The lat-
ter are thermophilic organisms and they may be found, for example, in hot volcan-
ic springs which often contain sulphur compounds and so represent a most extreme
environment. Various bacteria and other microorganisms can tolerate and multiply in
most unpromising conditions, for example in quite acid mine waters, and there are
others which exist in alkaline environments, with or without free oxygen and often
utilizing very unusual nutrients.
