Micro Midterm #1 Chapter 6

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-reproduction of prokaryotic cells into two daughter cells.
-When we talk about it we are really referring to the number of cells, not the size of the cells. Microbes that are “growing” are increasing in number, accumulating into colonies of hundreds of thousands of cells, or populations of billions of cells

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Microbial Growth

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Prokaryotic cell reproduction by division into two daughter cells.

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Binary fission

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The requirements for microbial growth can be divided into two main categories: physical and chemical. Physical aspects include temperature, pH, and osmotic pressure. Chemical requirements include sources of carbon, nitrogen, sulfur, phosphorus, trace elements, oxygen, and organic growth factors.

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4 phases of microbial growth

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Lag phase
Log phase
Stationary phase
Death phase

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period of little or no cell division; can last for 1 hour or several days.

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the lage phase

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cellular reproduction is most active during this period; cells begin to divide and enter a period of growth, or logarithmic increase.

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the log phase

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the growth rate slows, the number of microbial deaths balances the number of new cells, and the population stabilizes.
 exhaustion of nutrients, accumulation of waste products, and harmful changes in pH may all play a role.

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the stationary phase

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number of deaths eventually exceeds the number of new cells formed; phase continues until the population is diminished to a tiny fraction of the number of cells in the previous phase, or the population dies out entirely.

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the death phase

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The time required for a cell or population to double in number.

Number of generations = log number of cells(end) - log number of cells(beginning)
0.301 (which is the log of 2; 1 cell divides into two).

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generation time

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1.Psychrophiles: cold-loving
2.Mesophiles: moderate- temperature loving
3.Thermophiles: heat-loving
4.Hyperthermophiles/extreme thermophiles: live in 80c or higher.

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temperature

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Most bacteria grow between pH 6.5 and 7.5
Molds and yeasts grow between pH 5 and 6
Acidophiles grow in acidic environments,tolerant of acidic environment

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pH

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Hypertonic environments, increase salt or sugar, cause plasmolysis
Extreme or obligate halophiles require high osmotic pressure
Facultative halophiles tolerate high osmotic pressure
Obligate halophiles: require the salt.
Facultative: do not need salt, but can adapt. e.f. E. Coli

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Osmotic pressure

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A.Obligate aerobes: require oxygen
B.Facultative anaerobes: can use oxygen when present, but if not, it will use fermentation
C.Aerotolerant anaerobes: cannot use oxygen for growth, but can tolerate it.
D.Microaerophiles: need oxygen, grow deep.

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oxygen

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Structural organic molecules, energy source
Chemoheterotrophs use organic carbon sources
Autotrophs use CO2
need carbon also nitrogen, sulfur, and phosphorus

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carbon

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three primary groups on the basis of their preferred range of temperature

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Psychrophile
Mesophile
Thermophile

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An organism that grows best at about 15°C and does not grow above 20°C; a cold-loving microbe.

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Psychrophile

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An organism that grows between about 10°C and 50°C; a moderate-temperature–loving microbe.

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Mesophile

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An organism whose optimum growth temperature is between 50°C and 60°C; a heat loving microbe.

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Thermophile

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An organism whose optimum growth temperature is at least 80°C; also called extreme thermophile.
-members of the Archaea

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Extreme thermophile

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with an optimum growth temperature of 25 to 40°C, are the most common type of microbe.

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Mesophiles

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Most bacteria grow best in a narrow pH range near neutrality, between pH 6.5 and 7.5. Chemoautotrophic bacteria can survive at a pH value of

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pH

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A bacterium that grows below pH 4; tolerant of acidity.

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Acidophile

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the force with which a solvent moves from a solution of lower solute concentration to a solution of higher solute concentration.

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Osmotic Pressure

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An organism that requires a high salt concentration for growth.

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Extreme halophile

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An organism that requires high osmotic pressures such as high concentrations of NaCl; often require nearly 30% salt,

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Obligate halophile

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An organism capable of growth in, but not requiring, 1–2% salt.

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Facultative halophile

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one of the most important requirements for microbial growth; Carbon is the structural backbone of living matter; it is needed for all the organic compounds that make up a living cell.

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carbon

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get most of their carbon from the source of their energy—organic materials such as proteins, carbohydrates, and lipids.

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Chemoheterotrophs

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derive their carbon from carbon dioxide

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Chemoautotrophs and photoautotrophs

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3 other elements are needed by microorganisms for the synthesis of cellular material.
 protein synthesis requires considerable amounts of nitrogen as well as some sulfur. The syntheses of DNA and RNA also require nitrogen and some phosphorus, as does the synthesis of ATP.

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Nitrogen, Sulfur, and Phosphorus

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Organisms use nitrogen primarily to form the amino group of the amino acids of proteins.
 nitrogen fixation - The conversion of nitrogen (N2) into ammonia; Ex. is photosynthesizing cyanobacteria.

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Nitrogen

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is used to synthesize sulfur-containing amino acids and vitamins such as thiamine and biotin

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Sulfur

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is essential for the synthesis of nucleic acids and the phospholipids of cell membranes; found in the energy bonds of ATP.

Potassium, magnesium, and calcium are also elements that microorganisms require, often as cofactors for enzymes.

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Phosphorus

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

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Oxygen

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An organism that requires molecular oxygen (O2) to live.

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obligate aerobe

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An organism that can grow with or without molecular oxygen (O2).

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facultative anaerobe

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4 Toxic forms of oxygen

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singlet oxygen

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Highly reactive molecular oxygen (O2–).

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singlet oxygen

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A toxic form of oxygen (O2–) formed during aerobic respiration.

superoxide dismutase (SOD) - An enzyme that destroys superoxide free radicals.

 Aerobic bacteria, facultative anaerobes growing aerobically, and aerotolerant anaerobes (discussed shortly) produce SOD, with which they convert the superoxide free radical into molecular oxygen (O2) and hydrogen peroxide (H2O2).

O2– + O2– + 2 H+ → H2O2 + O2

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superoxide free radical

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An enzyme that destroys superoxide free radicals.

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superoxide dismutase (SOD

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. The hydrogen peroxide produced in this reaction contains the peroxide anion O22– and is also toxic. Because the hydrogen peroxide produced during normal aerobic respiration is toxic, microbes have developed enzymes to neutralize it. The most familiar of these is catalase, which converts it into water and oxygen.

2 H2O2 → 2 H2O + O2

The other enzyme that breaks down hydrogen peroxide is peroxidase, which differs from catalase in that its reaction does not produce oxygen.

H2O2 + 2 H+ → 2 H2O

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peroxide anion
peroxidase

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A toxic form of oxygen (OH•) formed in cytoplasm by ionizing radiation and aerobic respiration.

These toxic forms of oxygen are an essential component of one of the body’s most important defenses against pathogens, phagocytes. In the phagolysosome of the phagocytic cell, ingested pathogens are killed by exposure to these toxic form of oxygen.


aerotolerant anaerobe  An organism that does not use molecular oxygen (O2) but is not affected by its presence.

microaerophile  An organism that grows best in an environment with less molecular oxygen (O2) than is normally found in air.

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hydroxyl radical

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An organism that does not use molecular oxygen (O2) but is not affected by its presence.

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aerotolerant anaerobe

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An organism that grows best in an environment with less molecular oxygen (O2) than is normally found in air.

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microaerophile

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exact chemical composition is known

usually reserved for laboratory experimental work or for the growth of autotrophic bacteria

To support microbial growth, a medium must provide an energy source, as well as sources of carbon, nitrogen, sulfur, phosphorus, and any organic growth factors the organism is unable to synthesize.

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Chemically defined media

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A culture medium in which the exact chemical composition is not known.

made up of nutrients, extracts from yeast, meat, or plants. Chemical composition varies slightly.

Most heterotrophic bacteria and fungi, such as you would work with in an introductory lab course, are routinely grown on complex media.

In complex media, the energy, carbon, nitrogen, and sulfur requirements of the growing microorganisms are primarily provided by protein.

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Complex media

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PEQ Justify the use of each of the following: aerobic techniques, candle jars, differential media, and selective media. Use an example of an organism you might be looking for, with each example (use appropriate nomenclature)

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.In clinical and public health microbiology, it is frequently necessary to detect the presence of specific microorganisms associated with disease or poor sanitation.

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PEQ Cont'd -A culture medium designed to suppress the growth of unwanted microorganisms and encourage the growth of desired ones.
-For example, bismuth sulfite agar is one medium used to isolate the typhoid bacterium, the gram-negative Salmonella typhi (tī'fē), from feces.

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selective medium

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PEQ CONT'D A solid culture medium that makes it easier to distinguish colonies of the desired organism.
-Streptococcus pyogenes (pī-äj'en-ēz), the bacterium that causes strep throat, show a clear ring around their colonies where they have lysed the surrounding blood cells.

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differential medium

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PEQ Cont'd more often commercially available chemical packets are used to generate carbon dioxide atmospheres in containers.
-microaerophilic Campylobacter bacteria.

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candle jars

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PEQ Cont'd Many clinical laboratories have special carbon dioxide incubators in which to grow aerobic bacteria that require concentrations of CO2 higher or lower than that found in the atmosphere.
-Mycobacterium leprae

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aerobic techniques

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Know 4 different “direct methods” for measuring microbial growth

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•Plate count: measures number of viable cells
•Serial dilutions: original inoculum diluted sveral times
•Pour plate
•Spread plate
•Filtration
•MPN
•Direct microscopic count

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reflects the number of viable microbes and assumes that each bacterium grows into a single colony; plate counts are reported as number of colony-forming units (CFU).
-may be done by either the pour plate method or the spread plate method.

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plate count

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bacteria are retained on the surface of a membrane filter and then transferred to a culture medium to grow and subsequently be counted.

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filtration

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method can be used for microbes that will grow in a liquid medium; it is a statistical estimation.

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most probable number (MPN)

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the microbes in a measured volume of a bacterial suspension are counted with the use of a specially designed slide.

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direct microscopic count,

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the cloudiness of a suspension.

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turbidity

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A method of inoculating a solid nutrient medium by mixing bacteria in the melted medium and pouring the medium into a Petri dish to solidify.

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pour plate method

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A plate count method in which inoculum is spread over the surface of a solid culture medium.

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spread plate method

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The process of diluting a sample several times.

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serial dilution

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A method of isolating a culture by spreading microorganisms over the surface of a solid culture medium.

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streak plate method

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CO2 in proportion to # of bacteria

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metabolic activity

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filtered, dried, then weighed

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dry weigth

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how are microbes preserved?

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Microbes can be preserved for long periods of time by deep-freezing or lyophilization (freeze-drying).

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The time required for a cell or population to double in number.

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generation time

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A method of isolating a culture by spreading microorganisms over the surface of a solid culture medium.

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streak plate method

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The process of diluting a sample several times.

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serial dilution

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A statistical determination of the number of coliforms per 100 ml of water or 100 g of food.

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most probable number (MPN) method

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The cloudiness of a suspension.

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turbidity

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A method of inoculating a solid nutrient medium by mixing bacteria in the melted medium and pouring the medium into a Petri dish to solidify.

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pour plate method

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Laboratory techniques used to minimize contamination.

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aseptic techniques

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A bacterium that grows below pH 4.

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acidophile

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A highly phagocytic granulocyte; also called polymorphonuclear leukocyte (PMN) or polymorph

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neutrophil

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An organism that requires molecular oxygen (O2) to live.

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obligate aerobe

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An organism that does not use molecular oxygen (O2) and is killed in the presence of O2.

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obligate anaerobe

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An organism that requires high osmotic pressures such as high concentrations of NaCl.

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obligate halophile

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An organism that can grow with or without molecular oxygen (O2).

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facultative anaerobe

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An organism capable of growth in, but not requiring, salt.

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facultative halophile

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An organism requiring molecular oxygen (O2) for growth.

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aerobe

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An organism that does not require molecular oxygen (O2) for growth.

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anaerobe

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An organism that grows best in an environment with less molecular oxygen (O2) than is normally found in air.

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microaerophile

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A microorganism that grows best at relatively high CO2 concentrations.

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capnophile

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An organism that does not use molecular oxygen (O2) but is not affected by its presence.

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aerotolerant anaerobe

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Loss of water from a cell in a hypertonic environment.

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plasmolysis

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An organism that requires a high salt concentration for growth.

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halophile

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An organism that grows best at about 15 degrees C and does not grow above 20 degrees C; a cold-loving microbe.

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psychrophile

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Grow between 0°C and 20-30°C

Cause food spoilage


An organism that is capable of growth between about 0 degrees C and 30 degrees C.

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pscyhrotroph

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A granulocyte (leukocyte) that readily takes up basic dye and is not phagocytic; has receptors for IgE Fc regions.

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basophil

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An organism that grows between about 10 degrees C and 50degrees C; a moderate-temperature-loving microbe.

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mesophile

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An organism whose optimum growth temperature is between 50 degrees C and 60 degrees C; a heat loving microbe.

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thermophile

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thincrease in number of cells, not cell size

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Microbial growth

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Complex polysaccharide
Used as solidifying agent for culture media in Petri plates, slants, and deeps
Generally not metabolized by microbes
Liquefies at 100°C
Solidifies ~40°C

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agar

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increase in number of cells, not cell size

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microbial growth

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Prokaryotic cell reproduction by division into two daughter cells

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binary fission

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Two main catergories of requirements for microbial growth

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1. Physical aspects
2. Chemical requirements

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New cell numbers balanced by death of cells

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Stationary phase

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No cell division, but intense metabolic activity

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Lag Phase

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A logarithmic plot of the population produces an ascending straigth line

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Log Phase

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If 100 cells growing for 5 hours produced 1,720,320 cells:

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log 1,720,320 - log 10 / 0.301 = 14 generations

60 min.hr X 5 hours / 14 generations = 21 mintues/generation

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Suppose 900 of the same species were grown under hte same conditions as the previous example, except that the preservative was added to the culture medium. After 15 hours there was 3,276,800 cells. What is the generation time?

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log 3,276,800 - log 900 / 0.301 = 12 generations

60 min/hr X 15 hours / 12 generations = 75 minutes/generation

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microbes are classifed into groups based on these 5 items

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1. temperature
2. pH
3. osmotic pressure
4. oxygen
5. CO2 requirements

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4 toxic forms of oxygen

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1. singlet oxygen
2. superoxide free radical
3. peroxide anion / peroxidase
4. hydroxyl radical

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Adapted to high salt concentration, which are required for growth

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extreme halophile

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the general term used for organisms capable of growth at 0C

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Psychrophile

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Capable of growth at high temperatures; optimum 50-60C

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Thermophile

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Used in media to neutralize acids

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buffer

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a phenomenon that occurs when bacteria are placed in high salt concentration

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plasmolysis

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term used in text for organsims that grow well at refrigerator temperature; optimum growth is at temperatures of 20-30C

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Psychrotroph

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microbes that grow better at hight CO2 concetrations

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Capnophile

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members of the archaea with an optimum growth temperature of 80C or higher

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hyperthermophile

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the matrix that makes up a biofilm

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hydrogel

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refers to the number of cells

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growth

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a population of bacteria in which all cells divide at approximately the same

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synchronous growth

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measurement of turbidity in which a beam of light is transmitted through a bacterial suspension to a light-sensitive detector

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spectrophotometry

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cultures of microorganisms maintained soley for the purpose of keeping microorganisms in a viable condition by subculture, as necessary, into fresh culture

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stock cultures

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single species

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pure culture

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.

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preserved culture

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microbe classified as extremophile that thrive in alkaline environments at pH 9-11

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alkaliphile

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toxic anion with an unpaired element

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superoxides

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distended or swollen, especially due to high fluid content

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turgid

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an enzyme acting upon hydrogen peroxide

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catalase

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Rhizobium bacteria do this in symbiosis with leguminious plants

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nitrogen fixation

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requires atmospheric oxygen to grow

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obligate aerobe

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requires atmospheric oxygen, but in lower than normal concentrations.

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microaerophile

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does not use oxygen, but grows readily in its presence

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aerotolerant anaerobe

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does not use oxygen and usually finds it toxic.

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obligate anaerobe

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breakds down hydrogen peroxide without generation of oxygen

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peroxidase

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formed in cytoplasm by ionizing radiation

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hydroxyl radical

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an enzyme that converts hydrogen peroxide into oxygen and water

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catalase

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the toxic form of oxygen neutralized by superoxide dismutase

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superoxide radicals

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a component added to some culture media that makes the Petri plate into a self-contained anaerobic chamber

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oxyrase

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synonym for superoxide anions

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superoxide radicals

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isolation method for getting pure cultures' uses an inoculating loop to trace a pattern of inoculum on a solid medium

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streak plate

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colonies grow on agar surface identification

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spread plate

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used to increase the numbers of a small minority of microorganisms in a mixed culture to arrive at a detectable level of microorganisms

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enrichment culture

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preservation method that uses quick-freezing and a high vacuum

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lyophilization

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accumulations of microbes large enough to see without a microscope

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colonies

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microbes added to initiate growth

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inoculum

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used to grow obligate anaerobes

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reducing media

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designed to suppress the growth of unwanted bacteria and to encourage growth of desired microbes

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selective media

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generally contain ingredients such as sodium thioglycolate that chmically combine with dissolved oxygen

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reducing media

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nutrients are digest or extracts; exact chemical composition varies slightly from batch to batch

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complex media

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