Chapter 6 Microbial Nutrition & Growth

bacteria that must have high salt for cell growth (up to 30% salt) e.g Halobacterium

Obligate halophiles

What is the difference between complex media and defined media?

Complex media- media for which the exact chemical composition varies slightly from batch to batch. Defined media- a medium whose exact chemical composition is known.

Which of the following methods is best for counting fecal bacteria from a stream to determine the safety of the water for drinking? a. dry weight b. viable plate counts c. membrane filtration d. turbidity

c. membrane filtration

Which of the following terms best describes an organism that cannot exist in the presence of oxygen? a. obligate aerobe b. facultative aerobe c. obligate anaerobe d. facultative anaerobe

c. obligate anaerobe

________________ pigments protect many phototrophic organisms from photochemically produced singlet oxygen.

carotenoids

Two cultures of a facultative anaerobe are grown under identical conditions, except that one was exposed to oxygen and the other was completely deprived of oxygen. What differences would you expect to see between the dry weights of the cultures? Why?

the dry weight of the culture frown in the presence of O2 is much greater than the dry weight grown in the absence of O2. Oxygen is requred for complete aerobic respiration of metabolites and without it much less chemical energy is recovered per molecule, and metabolites are depleted in fewer generations than are able to grow in presence of oxygen.

A scientific article describes a bacterium as an obligate microaerophilic chemoorganoheterotroph. Describe the oxygen and nutritional characteristics of the bacterium in everyday language.

-requires low levels of oxygen and cannot survive without this feature - requires organic compounds for carbon and energy and growth

A scientist inoculates a bacterium into a complex nutrient slant tube. The bacterium forms only a few colonies on the slanted surface but grows prolifically in the depth of the agar. Describe the oxygen requirements of the bacterium.

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If there are 47 cells in 1 l of sewage, how many cells are there in a liter?

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Which of the following can grow in a Petri plate on a laboratory table? a. an anaerobic bacterium b. an aerobic bacterium c. viruses on an agar surface d. all of the above

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Psychrotrophs

20c - 30c

Mesophiles

25c- 45c

Thermophiles

45c- 70c : Hot springs

Psychrophiles

5c - 15c : Arctic and antarctic regions

Hyperthermophiles

70c - 110c : Usually members of archae. Hydrothermal vents

Pasteurization is a technique that uses temperatures of about 72°C to neutralize potential pathogens in foods. What effect does this temperature have on the enzymes and cellular metabolism of pathogens? Why does the heat of pasteurization kill some microorganisms yet fail to affect thermophiles?

72 is the temperature that they grow best, at that temperature many proteins are denatured and metabolic pathways are shut down without functional protein. Thermophiles grow well under pasteurizing conditions.

Contrast the media described in Tables 6.3 and 6.4 (pp. 179 and 181). Why is E. coli medium described as defined, whereas MacConkey medium and blood agar are defined as complex?

A defined medium (also known as synthetic medium) provides exact known amounts of nutrients for the growth of a particular microbe. Complex media contain a variety of growth factors.

Bacteria and fungi that grow best in acidic habitats

Acidophiles

Support or refute the following statement: Microbes cannot tolerate the low pH of the human stomach.

Acidophiles : bacteria and fungi that grow best in acidic habitats (1-2) -ex. stomach acid (pH 2)

Live in alkaline soils and water up to pH 11.5

Alkalinophiles

Why is agar used in microbiology?

An agar plate or Petri dish is used to provide a growth medium using a mix of agar and other nutrients in which microorganisms, including bacteria and fungi, can be cultured and observed under the microscope.

Obligate aerobes

Bacteria must grow with oxygen (essential for growth)

Obligate anaerobes

Bacteria must grow without oxygen (forms of oxygen are toxic to their cell structure)

organisms that live under extreme pressure

Barophiles

Heterotrophs

Catabolize reduced organic molecules as source of carbon

Can tolerate high salt environments

Facultative halophiles

blood agar

For culture of fastidious microorganisms and differentiation of hemolytic microorganisms Partial digestion of blood: alpha- hemolysis; complete digestion of blood: beta-hemolysis; no digestion of blood: gamma-hemolysis

MacConkey medium

For the culture and differentiation of enteric bacteria based on the ability to ferment lactose Lactose fermenters produce red to pink colonies; non-lactose-fermenters form colorless or transparent colonies

Draw and label the four distinct phases of a bacterial growth curve. Describe what is happening within the culture as it passes through the phases.

Min, optimum, max

Bacteria and protozoa that grow best in a narrow range around neutral pH (6.5-7.5)

Neutrophiles

Factors influencing growth

Oxygen Temperature pH Water availability

Environmental factors that influence microbes e.g. gas needs

Oxygen can transform into toxic products: (o2) (superoxide) (peroxide) (hydroxyls) can destroy cells. -Need enzymes to capture and neutralize toxic products. (catalase, superoxide dimutase) -Aerobic, facultative anaerobic organisms have these enzymes -Anaerobic organisms do not have these enzymes

Superoxide dismutase a. causes hydrogen peroxide to become toxic. b. detoxifies superoxide radicals. c. neutralizes singlet oxygen. d. is missing in aerobes.

b. detoxifies superoxide radicals.

Why must media, vessels, and instruments be sterilized before they are used for microbiological procedures?

To avoid contamination

High temperature affects the shape of particular molecules. How does this affect the life of a microbe?

Too high temperature denatures proteins and cell membranes become too fluid - Too low temperature results in rigid and fragile membranes

Autotrophs

Use of inorganic source of carbon (CO2)

Barophiles a. cannot cause diseases in humans. b. live at normal barometric pressure. c. die if put under high pressure. d. thrive in warm air.

a. cannot cause diseases in humans.

Lyophilization can be described as a. freeze-drying. b. deep-freezing. c. refrigeration. d. pickling.

a. freeze-drying.

In a defined medium a. the exact chemical composition of the medium is known. b. agar is available for microbial nutrition. c. blood may be included. d. organic chemicals are excluded.

a. the exact chemical composition of the medium is known.

undergo aerobic respiration

aerobes

do not use aerobic metabolism but have some enzymes that detoxify oxygen's poisonous forms

aerotolerant anaerobes

do not use aerobic metabolism

anaerobes

A microbiologist describes an organism as a chemoheterotrophic, aerotolerant, mesophilic, facultatively halophilic bacillus. Describe the organism's metabolic and structural features in plain English.

chemoheterotrophic - use organic compounds for energy and carbon aerotolerant- prefers anaerobic conditions but can tolerate low levels of oxygen mesophilic- optimum growth temp 25c-45c Facultative - can live with or without something Halophile - require saline environment rod shaped microbe that eats food and is able to survive in the presence of oxygen that grows best at moderate temperatures and that can grow in high salt concentrations

Organisms that preferentially may thrive in icy waters are described as. a. barophiles. b. thermophiles. c. mesophiles. d. psychrophiles

d. psychrophiles

differential media

distinguish among groups of bacteria

Selective media

either inhibit the growth of unwanted microorgan- isms or favor the growth of particular microbes

can perform fermentation or anaerobic respiration or aerobic respiration

facultative anaerobes

Obligate ________________ exist in salt ponds because of their ability to withstand high osmotic pressure.

halophiles

Cells that shrink in hypertonic solutions such as saltwater are responding to ________________ pressure.

osmotic

aerobes that require oxygen levels from 2 to 10%

microaerophiles

The lowest temperature at which a microbe continues to metabolize is called its ________________.

minimum growth temperature; min max- no growth optimum