Bacteria: Bacteria are relatively simple, single-celled (unicellular) organisms.

Because their
genetic material is not enclosed in a special nuclear membrane, bacterial cells are called
prokaryotes, from Greek words meaning prenucleus. Prokaryotes which include both bacteria
and archaea. Bacterial cells generally appear in one of several shapes. Bacillus (rodlike), coccus
(spherical or ovoid), and spiral (corkscrew or curved) are among the most common shapes,
but some bacteria are starshaped or square. Individual bacteria may form pairs, chains,
clusters, or other groupings; such formations are usually characteristic of a particular genus or
species of bacteria. Bacteria are enclosed in cell walls that are largely composed of a
carbohydrate and protein complex called peptidoglycan. (By contrast, cellulose is the main
substance of plant and algal cell walls.) Bacteria generally reproduce by dividing into two equal
cells; this process is called binary fission. For nutrition, most bacteria use organic chemicals,
which in nature can be derived from either dead or living organisms. Some bacteria can
manufacture their own food by photosynthesis, and some can derive nutrition from inorganic
substances. Many bacteria can “swim” by using moving appendages called flagella. Archaea Like
bacteria, archaea consist of prokaryotic cells, but if they have cell walls, the walls lack
peptidoglycan. Archaea, often found in extreme environments, are divided into three main
groups. The methanogens produce methane as a waste product from respiration. The
extreme halophiles (halo = salt; philic = loving) live in extremely salty environments such as
the Great Salt Lake and the Dead Sea. The extreme thermophiles (therm = heat) live in
hot sulfurous water, such as hot springs at Yellowstone National Park. Archaea are not
known to cause disease in humans. The most important knowledge that should emerge
from a microbiology course is the profound influence microorganisms have on all aspects
of the earth and its residents. For billions of years, microbes have extensively shaped the
development of the earth’s habitats and the evolution of other life forms. It is
understandable that scientists searching for life on other planets first look for signs of
microorganisms. Microbes are an essential factor in many natural phenomena that make life
possible on Earth. Microbes can be found almost everywhere (ubiquitous), from deep in the
earth’s crust, to the polar ice caps and oceans, to the bodies of plants and animals. Being
mostly invisible, the actions of microorganisms are usually not as obvious or familiar as those
of larger plants and animals. They make up for their small size by occurring in large numbers
and living in places that many other organisms cannot survive. Above all, they play central
roles in the earth’s landscape that are essential to life.

Impact of Microorganisms: ● Microbes are essential for life as we know it and the processes
that support life (e.g., in biogeochemical cycles and plant and/or animal microbiota). ●
Microorganisms provide essential models that give us fundamental knowledge about life
processes. ● Humans utilize and harness microorganisms and their products. ● Because the
true diversity of microbial life is largely unknown, its effects and potential benefits have not
been fully explored. Clearly, microorganisms pervade our lives in both an everyday, mundane
sense and in a far wider view. However, the majority of microorganisms actually help
maintain the balance of life in our environment. Marine and freshwater microorganisms
form the basis of the food chain in oceans, lakes, and rivers. Soil microbes help break
down wastes and incorporate nitrogen gas from the air into organic compounds, thereby
recycling chemical elements among soil, water, living organisms, and air. Certain microbes play
important roles in photosynthesis, a food and oxygen-generating process that is critical to life on
Earth. Humans and many other animals depend on the microbes in their intestines for digestion
and the synthesis of some vitamins that their bodies require, including some B vitamins
for metabolism and vitamin K for blood clotting. Microorganisms also have many commercial
applications. They are used in the synthesis of such chemical products as vitamins, organic
acids, enzymes, alcohols, and many drugs. For example, microbes are used to produce acetone
and butanol, and the vitamins B2 (riboflavin) and B12 (cobalamin) are made biochemically. The
process by which microbes produce acetone and butanol was discovered in 1914 by Chaim
Weizmann, a Russian-born chemist working in England. With the outbreak of World War I
in August of that year, the production of acetone became very important for making
cordite (a smokeless form of gunpowder used in munitions). Weizmann’s discovery played a
significant role in determining the outcome of the war. The food industry also uses microbes
in producing, for example, vinegar, sauerkraut, pickles, soy sauce, cheese, yogurt, bread, and
alcoholic beverages. Also eat food that derives flavor from microbial action, and, in many cases,
even eat microorganisms themselves. In addition, enzymes from microbes can now be
manipulated to cause the microbes to produce substances they normally don’t synthesize,
including cellulose, digestive aids, and drain cleaner, plus important therapeutic substances
such as insulin. Microbial enzymes may even have helped produce your favorite pair of jeans.
Though only a minority of microorganisms are pathogenic (disease-producing), practical
knowledge of microbes is necessary for medicine and the related health sciences. We are
vaccinated with altered microbes to prevent diseases that are caused by those very same
microbes. We treat various medical conditions with drugs produced by microbes; we dust
our plants with insecticides of microbial origin; and we use microorganisms as tiny factories
to churn out various industrial chemicals and plastics. We wash our clothes with detergents
containing microbe-produced enzymes. We depend upon microbes for many facets of life—one
might say even for life itself. No one can emerge from a microbiology course without a changed
view of the world and of themselves.