Anatomy of Bacteria

MorphologyStructureFunction

Binary Fission

• “a method of asexual reproduction involving halving of the nucleus and cytoplasm of the cell followed by the development of each half into a new individual”

• septum• progeny cells• generation time

Morphology

• Size

• Shape

• Arrangement

Size

• prokaryotic (bacteria) cells are very small compared to eukaryotic cells

• prokaryotic cells are the most abundant form of life on earth

• prokaryotic cells can survive in conditions that are too extreme for eukaryotic cells

Shape

• Readings question one:

What are the three basic shapes that most bacteria exhibit?

Spiral(Vibrio, Spirillum, Spirochete)

• Vibrio: “curved or bent rods that resemble commas”

• Spirillum: “a corkscrew shape with a rigid cell wall and hair-like projections called flagella that assist in movement”

• Spirochete: “a flexible cell wall but no flagella in the traditional sense. Movement occurs by contractions (undulating) of long filaments (endoflagella) that run the length of the cell.”

Arrangement

• Readings question two:What are the three basic arrangements that most bacteria exhibit?

Additional arrangements:Tetracocci: “grouping of four spherical shaped

cells”Sarcinae: “a cube-like packet of eight spherica

bacteria”

Structure and Function• up until the 1950’s prokaryotes were believed to

simply be “bags of enzymes”• prokaryotes have a simpler construction than

eukaryotes• prokaryotic cell has 5 essential structural

components:– Nucleoid (bacterial chromosome)– Ribosomes– Cell membrane– Cell wall– Capsule

Nucleoid

• bacterial chromosome• typically one large circular molecule of DNA• floats freely in the cytoplasm• genetic control center of the cell• determines all of the properties and functions

of the bacterium

Ribosomes

• proteins and RNA• prokaryotic ribosomes are smaller than

eukaryotic ribosomes• protein synthesis• “granular” appearance

Cell Membrane and Cell Wall

• Readings question three:

What is the difference between the cell membrane and the cell wall?

Capsule

• “the membrane that surrounds some bacterial cells; a loose gel-like structure that, in pathogenic bacteria, helps to protect against phagocytosis”

• glycocalyx• slime layer

Cytoplasm

• Readings question four:• What is the cytoplasm of prokaryotic cells?

• primary structures: nucleoid and ribosomes

• plasmids: extrachromosomal pieces of DNA

Endospores

• “a thick-walled spore within a bacterium”

Endospores

• produced by the bacterium to help it survive in an unfavorable environment

• formed by vegetative cells- “sporulation”• one of the most resistant forms of life

• germination

Clostridium tetani

• deep wound punctures that become anoxic

• tetanus toxin spreads and causes disease

• spastic paralysis and can result in death

Clostridium botulinum

• botulinum toxin in improperly preserved foods

• botulism can result in death due to respiratory failure as a result of muscle paralysis

Clostrideium perfringens

• most prevalent reported cause of food poisoning

• enterotoxins in the intestines

• diarrhea and intestinal cramps with no fever or vomiting

Flagella

• protein structures attached to the cell surface that resemble “whip-like” appendages

• distributed in distinguishing patterns

• flagella of prokaryotic cells differ from eukaryotic cells

Pili (Fimbriae)

• short, hair-like structures on the surface of prokaryotic cells composed of protein

• shorter, thinner, and straighter than flagella• allow bacteria to attach to surfaces• e.g. Neisseria gonorrhoeae

Gram-staining

• Readings question five:

• What is the purpose of gram-staining? What are the characteristics of gram-positive bacteria and gram-negative bacteria?

Physiology of Bacteria

Bacterial Growth

Bacterial Colony

• “a visible group of bacteria growing on a solid medium, presumably arising from a single microorganism”

Requirements for Growth

• Physical: temperature, pH, light, osmotic pressure, moisture

• Chemical: carbon, nitrogen, sulfur, phosphorus, trace elements, oxygen

Temperature

• Readings question three:

What are psychrophiles, mesophiles, and thermophiles?

Psychrophiles

• Desulfofrigus oceanense (Arctic and Antarctic Oceans)

Mesophiles

E. coli

Thermophiles

Fossilized Microbes from Yellowstone’s Hot Springs

Temperatures

• Minimum: “temperature below which bacterial growth will not take place”

• Optimum: “temperature at which organisms grow best”

• Maximum: “temperature above which bacterial growth will not take place”

• What are the embalming implications associated with the temperature preference of bacteria?

pH

• Readings question four:

Describe the pH scale.

Acidophiles: bacteria that are remarkably tolerant of acidity

Light

• Cyanobacteria: oxygen producing prokaryotes– thrive in the presence of light

• Yeasts and Molds– prefer dark areas

• Some bacteria are destroyed by ultraviolet light.

Osmotic Pressure

• “pressure that develops when two solutions of different concentrations are separated by a semi-permeable membrane”

• microorganisms require water for growth and are made up of 80-90% water

• high osmotic pressure removes necessary water from a cell

• plasmolysis• hypertonic solutions

Moisture

• maximum, optimum and minimum requirement for all microorganisms

• Pathogenic bacteria are usually found in the body’s tissues

• Fungal diseases are usually found on the body surface.

Chemical Requirements

• Readings question two:

Describe the differences between autotrophic bacteria and heterotrophic bacteria.

Heterotrophic Bacteria

• 3 categories:– 1) strict (obligate) saprophyte– 2) strict (obligate) parasite– 3) facultative bacteria:• Facultative saprophyte: “prefers live organic matter as

a source of nutrition but can adapt to the use of dead organic matter under certain conditions”• Facultative parasite: capable of living and growing with

the nutrients that its host provides

Carbon

• one of the most important requirements for microbial growth

• structural backbone of living matter• needed for all the organic compounds that

make up a living cell• ½ of the “dry weight” of a bacterial cell is

carbon

Nitrogen, Sulfur, and Phosphorus

• needed by microorganisms for the synthesis of cellular material

• e.g. protein, DNA, RNA, ATP

Trace Elements

• iron, copper, and zinc

• essential for the function of certain enzymes

Oxygen

• Microbes that use molecular oxygen (aerobes) produce more energy from nutrients than microbes that do not use oxygen (anaerobes)

• Reading question two:Describe the difference between obligate

aerobes and obligate anaerobes.

Microaerophilic Organisms

• “a microorganism that requires very little free oxygen”

• only grow in oxygen concentrations that are lower than those in air

• require about 2 – 10% free oxygen

Facultative Organisms

• Facultative Aerobes: “a microorganism that prefers an environment devoid of oxygen but has adapted so that it can live and grow in the presence of oxygen”

• Facultative Anaerobes: “a microorganism that prefers an oxygen environment but is capable of living and growing in its absence”– E.g. Bacillus anthracis, Corneybacterium

diphtheriae, Escherichia coli

Aerotolerant Organisms

• can grow in the presence or absence of oxygen– e.g. Streptococcus pyogenes

Microbial Associations

• normal flora (microbiota)• transient microbiota• symbiotic relationship: “organisms live in close

nutritional relationships; required by one or both members”– distinguished by the degree to which the host

organism is harmed

Mutualism

• “a symbiotic relationship in which organisms of two different species live in close association to the mutual benefit of each”– e.g. E. coli in the human digestive tract

Commensalism

• “the symbiotic relationship of two organisms of different species in which one gains some benefit such as protection or nourishment and the other is not harmed or benefited”– e.g. bacteria on skin surface; microorganisms

within the digestive tract

Parasitism

• “an interactive relationship between two organisms in which one is harmed and the other benefits”

• many disease-causing bacteria are parasites• typically the host is macroscopic and the

parasite is microscopic• roundworms and flatworms are parasites that

are large multi-cellular organisms

• Readings question five:

What is the synergistic effect?

Antagonism

• “mutual opposition or contrary action. The inhibition of one microorganism by another.”

• Involves competition among microbes• normal microbiota protect the host against

colonization by potentially pathogenic microbes

• normal flora produce substances harmful to the invading microbes (pH, oxygen)