Chapter 6- Microbial Nutrition and Growth (End of Chapter Questions)

How can regions within biofilms differ in their chemical content?

-

Microorganisms require phosphorus, sulfur, iron, and magnesium for metabolism. What specifically are these elements used for in microbial metabolism?

-

Some organisms require riboflavin (vitamin B2) to make FAD. For what purpose do they use FAD?

-

The bacterium Desulforudis audaxviatpr lives almost two miles underground, deriving energy from sulfate, acquiring electrons from hydrogen, and building organic molecules from inorganic carbon found in surrounding rocks. Describe the nutritional classifications of D. audaxviator

-

Why is agar used in microbiology?

- because most microbes cannot digest afar, therefore, agar media remain solid even when bacteria and fungi are growing on them - gives nutrients to bacteria that it needs to grow

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.

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.

A scientist describes an organism as chemoheterotrophic, aerotolerant, facultatively halophilic coccus. Describethe cells metabolic and structural features in plain English.

-chemeoheterotrophic means the microbe uses oxygen compounds and carbon for energy -aerotolerant mean the microbe can tolerate low levels of oxygen but prefers to be anaerobic -facultatively means the microbe can live with or without something -halophillic means that it requires a saline environment -coccus refers to its spherical shape -the spherical microbe 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

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

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

High temperature affects the shape of particular molecules. How does the 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

List three indirect methods of counting microbes

1. turbidity- As bacteria multiply in a liquid medium, the medium becomes turbid, or cloudy with cells. Use a spectrophotometer- a beam of light is transmitted through a bacterial suspension to a light-sensitive detector. As bacterial numbers increase, less light will reach the detector. 2. metabolic activity- Assumes that the amount of a certain metabolic product (acid or CO2) is in direct proportion to the number of bacteria present. For example, a microbiological assay in which acid production is used to determine amounts of vitamins. 3. dry weight- The fungus/bacteria is removed from the growth medium, filtered to remove extraneous material, and dried in a desiccator and then weighed.

List five direct ways of counting microbes

1. viable plate counts 2. membrane filtration 3. microscopic counts 4. electronic counters 5. Most Probable Number

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

47,000,000

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

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

a. cannot cause disease in humans

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

a. freeze drying

Quorum sensing is ________ a. the ability to respond to changes in population density b. a characteristic allowing secretion of a matrix c. dependent on direct contact among cells d. associated with colonies in broth culture

a. the ability to respond to changes in population density

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

The most reactive of the four toxic forms of oxygen is a. the hydoxyl radical b. the peroxide anion c. the superoxide radical d. singlet oxygen

a. the hydroxyl radical

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)

Which of the following is most useful in representing population growth on a graph a. logarithmic reproduction of the growth curve b. a semilogarithmic graph using a log scale on the y-axis c. an arithmetic graph of the lag phase followed by a logarithmic section for the long, stationary, and death phases d. none of the above would best represent a population growth curve

b. a semilogarithmic graph using a log scale on the y axis

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 above

b. an aerobic bacterium

Microaerophiles that grow best with a high concentration of carbon dioxide in addition to a low level of oxygen are called a. aerotolerant b. capnophiles c. facultative anaerobes d. fastidious

b. capnophiles

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

b. detoxifies superoxide radicals

Which of the following is not a growth factor for various microbes a. cholesterol b. water c. vitamins d. heme

b. water

How does a chemostat maintain a constant population size?

by having an open-system microbial culture of a fixed volume

A coulter counter is a(n) _________ a. statistical estimation using 15 dilution tubes and a table of numbers to estimate the number of bacteria per milimeter b. indirect method of counting microorganisms c. device that directly counts microbes as they pass through a tube in front of an electron detector d. device that directyly counts microbes that are differently stained with fluorescent dyes

c. device that directly counts microbes as they pass through a tube in front of an electron detector

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

c. obligate anaerobe

This statement "In the laboratory, sterile inoculating loop is moved across the agar surface in a culture dish, thinning a sample and isolating individuals," describes which of the following a. broth culture b. pour plate c. streak plate d. dilution

c. streak plate

________ pigments protect many phototrophic organisms from photochemically produced singlet oxygen

cartenoid

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. trubidity c. viable plate counts d. membrane filtration

d. membrane filtration

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

d. psychrophiles

All cells require a source of __________________ for redox reactions.

electrons

Microbes that reduce N2 to NH3 engage in nitrogen _______

fixation

______ are small organic molecules that are required in minute amounts for metabolism

growth factors

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

halophiles

Chemolithotrophs acquire electrons from ______ compounds

inorganic

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

minimum growth temperature

All cells recycle the essential element ____ from amino acids and nucleotides

nitrogen

Cells that shrink in hypertonic solutions such as salt water are responding to ______ pressure

osmotic

Explain the differences among photoautotrophs, organotrophs, and lithotrophs

photoautotrophs- energy source-light-makes own energy; carbon source-carbon dioxide; Plants, algae, and cyanobacteria us H2O to reduce CO2, producing O2 as a by product Photosynthetic green sulfur and purple sulfur bacteria do not use H2O nor produce O2 Ex: Chlorobium organotrophs- organisms that acquire electrons (typically as part of hydrogen atoms) from the same organic molecules that provide them carbon and energy lithotrophs- organisms that acquire electrons or hydrogen atoms from inorganic sources (such as H2, NO2-, H2S, and Fe2+) "rock" "nutrition"

A toxic form of oxygen, _______ oxygen, is a molecular oxygen with electrons that have been boosted to a higher energy state

singlet

A student observes a researcher streaking a plate numerous times, flaming the loop between streaks. The researcher is likely using the ______ method to isolate microorganisms

streak plate

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

the microbe is facultative anaerobic it can tolerate oxygen and grow there but it grows best in an area of low oxygen

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

to avoid contamination