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 one:

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 two:

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 three:

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 four: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)