MICROORGANISMS AND THEIR PLACE IN THE NATURAL ENVIRONMENT
An Overview of the Influence of Microbes on the Earth's Environment and Inhabitants.
The many and varied metabolic activities of microbes assure that they participate in chemical
reactions in almost every environment on earth. As discussed previously
microbes require an
energy producing system (including an electron acceptor) to sustain life and nutrients, including
liquid water, in order to grow and reproduce. Since microbes have been present on earth longer
than other organisms, they have evolved the ability to thrive in almost any environment that
meets these minimal criteria. Energy comes from one of two sources, light (photosynthesis) or
of reduced molecules. Oxidizable molecules may be organic (e.g. sugar, protein
or any of the other foods we humans relish) or a variety of inorganic molecules such as sulfur,
iron, hydrogen, carbon monoxide, or ammonia or even a combination of organic/inorganic
molecules. Microbes exist that prosper inside of eukaryotic cells, at temperatures of >100
the presence of toxic metals like copper or mercury, at pH's ~2.0 and ~11.0, down to 3.5 km
below the earth's surface and in saturated salt solutions at 0
C. Microbes have broadened the
environments they can live in by evolving enzymes that allow them to utilize sunlight for energy
as well as a diversity of electron donor/acceptors pairs so they can perform energy-yielding
oxidative reactions on available energy sources. That this evolution is ongoing is shown by the
isolation of microbes that can metabolize numerous man-made chemicals (
ones not found in
). The range of electron acceptors includes gaseous oxygen (like us), sulfate, nitrate,
nitrite, carbon dioxide, carbon monoxide, iron and magnesium. Indeed, evolutionary principles
predict that microbes should have evolved to utilize any niche meeting the minimal physical and
chemical requirements. Recently, bacteria that live ~3.5 km below the earth's surface in rocks at
high temperatures have been discovered. Since these conditions cover the entire earth, even that
portion under the oceans, these bacterial forms may make up the largest single mass of life on (or
Below is an abbreviated list of the roles microbes play in our lives:
They maintain soil fertility and soil tilth.
They clean up all the dead organic material; without them we would be up to our ears in
dead things, like our ancestors.
They fix gaseous nitrogen into forms that can be used by plants to maintain the fertility of
They can be used to extract minerals from ores.
They are the prime food for all the marine and freshwater life; even whales depend on
them directly or indirectly for their nutrition.
The Role of Microbes on the Earth