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The
Diversity of The World of Life
The Major Groups of Life etc.
Bacteria,
Including
Blue-Green Algae
(Domain Bacteria,
including Cyanobacteria)
(Here is an especially informative reference on various aspects of bacterial life -- A Scientific Breakdown on Bacteria -- discovered and shared by science student Tyler, as a special research project for his teacher, Michelle Adams)
Biology
Representatives
Actinomycetes spp.
(species) (fungus-like bacteria recycling materials in the soil, and
thus giving it its "earthy" smell, and producing antibiotics in
labs)
Agrobacterium spp.
(typically soil-borne bacteria, including one kind of bacterium that
lives in the "nodules" of legume plants, such as peas, and
converts nitrogen gas from the air into a form in the soil useful for
plant growth)
Bacillus spp. (including
species recycling materials in the soil or aiding digestion in our gut,
species causing anthrax or types of food poisoning, and a species useful
as a biological insecticide)
Borrelia burgdorferi
(causing Lyme disease)
Chlamydia
spp. (including a species causing a common sexually transmitted
disease)
Clostridium
spp. (including botulism & tetanus "pathogens",
disease-causing organisms)
Escherichia coli
("E. coli", common intestinal "flora", aiding
our digestion and producing vitamins for our bodies, although some strains
in nature can cause food poisoning)
Helicobacter pylori (causing
stomach ulcers)
Lactobacillus spp.
(converting milk into cheese, butter, or yogurt)
Mycobacterium spp.
(causing tuberculosis, leprosy, etc.)
Mycoplasma spp. (the
smallest known living things)
Neisseria spp. (including
a species causing the commonly sexually transmitted disease gonorrhea and
a species causing a serious "meningitis", an inflammation of the
"meninges", the membranes around the brain and spinal cord)
Nitrobacter & Nitrosomonas
spp. (involved in recycling forms of nitrogen, as from animal
wastes, in soils, pondwater, etc.)
Nostoc
spp.
(common species of blue-green algae that "fix" nitrogen from
the air into a form stable in the soil, where it can aid plant growth)
Oscillatoria
spp. (a commonly studied species of blue-green algae)
Pseudomonas spp.
(including species causing human infections, particularly in
hospitals, and resistant to most antibiotics)
Rickettsia
spp. (small primitive bacteria causing typhus etc.)
Salmonella spp. (including
species causing food poisoning or typhoid fever)
Shigella spp.
(including a dysentery pathogen)
Spirulina
spp. (commonly studied blue-green algae)
Staphylococcus
spp. (species causing acne, food poisoning, toxic shock syndrome,
often antibiotic-resistant "staph" infections, etc.)
Streptococcus
spp. (species causing "strep" throat, scarlet fever,
rheumatic fever, pneumonia, etc.)
Treponema pallidum (causing
syphilis)
Vibrio cholerae
(causing cholera)
Yersinia pestis
(causing bubonic plague)
Biology
ENVIRONMENTS
Bacteria are found virtually
everywhere on the planet: In salt- and fresh-water, in and on the
land, and in and on all other living things.
OVERALL STRUCTURE
Bacteria are almost always single-celled
organisms, each bacterium typically bounded by a cell wall, composed of
"peptidoglycan" -- a polymer (chain-like molecule) composed of
"polypeptides" (chains of "amino acids", the building
blocks of proteins) linked together with "polysaccharides"
(derived from sugar molecules). In most blue-green algae, the cell wall
has a protective coating of slimy mucilage.
Bacteria with a single,
thick cell wall of peptidoglycan stain purple with the dye called
"crystal violet"; these bacteria are called
"Gram-positive" (Dr. Gram was a Dutch bacteriologist).
Other bacteria, with a thin cell wall of peptidoglycan covered by an outer
cell wall, of carbohydrates (such as polysaccharides), proteins, and
lipids (fatty or oily compounds), do not stain purple with crysal violet;
these are the "Gram-negative" bacteria.
Note that the incorporation
of proteins or lipids in the cell wall of a bacterium is more biologically
"expensive" than just constructing a cell wall of
"cellulose" (a polysaccharide), as in higher plants.
The cell wall gives shape to
a bacterium -- a "coccus"
is round; a "bacillus",
rodlike; a "spirillum"
(less common), spiral-shaped. Most blue-green algae are round or disk-like.
Individual bacterial cells
may be associated in chains, filaments, sheets, or other groups (some
blue-green algae form hollow balls); however, these colonies are not truly multi-cellular organisms
-- there is
virtually no specialization or
"division of labor" between the cells (exceptions to this rule
include "heterocysts",
unusually large cells, within chains of blue-green algae cells that chemically "fix" nitrogen gas from the air, for the production
of nitrogen-rich proteins by all the cells within the chain -- such
nitrogen-fixation can enrich agricultural soils, as in Asian rice paddies,
which would otherwise require expensive nitrogen fertilizers).
Bacterial cells may be
equipped with hair-like "cilia", propellor-like
"flagella" (never on blue-green algae), adhesive
"capsules", or anchoring "pili" filaments (See the
note about "conjugation", below).
ENERGY
CAPTURE
Most bacteria are
"heterotrophic" (not producing their own food molecules):
They may be either "saprophytic" (feeding on -- and thus
recycling -- the wastes of
living creatures) or "parasitic" (feeding on the bodies of
living creatures).
However, many bacteria
are "autotrophic" (producing their own food molecules):
Some are "chemoautorophic" ("chemosynthetic"), releasing energy from chemical
reactions involving such materials as ammonia, carbon
monoxide, hydrogen gas, hydrogen sulfide, iron, or nitrates; other
bacteria are "photoautotrophic" ("photosynthetic"), capturing light-energy, by means
of the green pigment "chlorophyll a", embedded within membranes
(actually infoldings of the outer, cell membrane) inside the bacterial cell (Indeed, the
"chloroplasts" that conduct photosynthesis inside the cells of green plants
and some other organisms are thought
to have evolved from photosynthetic blue-green algae that were engulfed
but not digested by other prehistoric cells -- blue-green algae, like
chloroplasts, typically have stacks of disk-shaped membranes impregnated
with photosynthetic pigments). Incidentally, although blue-green algae
may indeed be blue-green (from a "phycocyanin" pigment), they
like other bacteria come in almost all the colors of the rainbow.
Some bacteria release
the energy from food molecules
"anaerobically" (that is, they do not require, and may not even
tolerate, the presence of oxygen); other bacteria "respire"
(release food energy) "aerobically" (that is, they require the
presence of oxygen -- what's more, the "mitochondria" that
conduct respiration inside the cells of eukaryotes
and, thus, act like "power plants" are thought to have evolved from
rickettsias or similar aerobic bacteria that were engulfed but
not digested by other prehistoric cells).
EXCHANGE
OF MATERIALS WITH THE ENVIRONMENT
Water, dissolved gases,
and other materials diffuse through the cell membranes of bacteria -- diffusion through any biological membrane is called "osmosis",
the "selective permeability" of the membrane controlling the
contents of the cell, within an often unpredictable environment.
Bacterial cells
exchange materials with and lose "body heat" to their
environment much more quickly than do the much larger cells of eukaryotes.
Consequently, most
bacteria have very quick life cycles, enormous reproduction rates,
and often enormous populations: Bacteria
can produce in short order as many individuals in a teaspoon as human
beings have produced on the entire planet!
INTERNAL
TRANSPORT
Materials simply
diffuse throughout the small cell of a bacterium: Unlike in eukaryotes,
there is no "cytoskeleton" and no "cytoplasmic
streaming".
DEVELOPMENTAL
CONTROL
The growth and
development of a bacterium is under genetic control, with considerable
biochemical "feedback", as from chemical-, light-, or even
magnetic-sensors of environmental conditions.
The growth and
development of bacteria might also be influenced
by "hormones" (biochemical messengers), even though those
molecules are typically used by multicellular organisms to
coordinate activities between different cells within the body.
ASEXUAL
REPRODUCTION
Bacteria typically
reproduce by "fission" (dividing in two), after having grown to
their maximum size.
The DNA in a bacterial
cell, unlike the cell of a eukaryote, is not
within a membrane-bound nucleus, is not bound to proteins, and is not
organized into chromosomes; rather, bacterial DNA forms loops, both a
large, tangled "nucleoid" and smaller, separate "plasmids".
Certain species of
bacteria can survive almost unlimited periods of unfavorable environmental
conditions by transforming into extremely durable "endospores". Blue-green
algae may form a thick wall or gelatinous coat to survive
harsh conditions.
"Transformation"
is the absorption of purified DNA from the environment into a bacterial
cell. Early experiments with
this process demonstrated that it is indeed DNA that controls heredity.
"Transduction"
is the transfer of genetic material from one bacterial cell to another via
a "bacteriophage" (a bacteria-infecting virus).
This process can be artificially manipulated for gene
"mapping".
"Conjugation"
is the one-way transfer of a "plasmid" (either a small, free
ring of DNA or part of the large, main ring of DNA in a bacterial cell) from the cell of one
"mating strain" of a bacteria to that of another (lacking that
plasmid). The cells are
pulled together by the donor's filamentous pilus, and they ultimately
contact one another via a "conjugation bridge".
Because there are not two donors of genetic material to an
offspring, this process is sometimes not considered true sexual
fertilization; and these two partners, not truly separate sexes.
Such valuable
pharmaceuticals as insulin, which controls diabetes, can be mass-produced
by using bacteria. The first step is to "genetically
engineer" plasmids (by
"recombinant DNA" techniques, involving enzymes) to produce the
desired biochemical. Then, the plasmids are replicated throughout populations of bacteria that reproduce asexually and, thus, are
genetically identical "clones".
SEXUAL
REPRODUCTION
As mentioned above,
reproduction in bacteria is typically considered asexual, at most
involving "mating strains", with a one-way transfer of genetic
material from one individual to another, not the contribution of genetic
material from two separate sexes to an offspring.
Representatives
The Major Groups of Life etc.
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