Chapter 7 Assignment

If a scientist is trying to grow an organism that the exact nutritional requirements are not known, it would be best to use this type of medium to grow it.

Complex

From the following list of food items and their water activities (aw), select the two that are the most susceptible to spoilage by most microorganisms.

Fresh fish, 0.99 Vegetable broth, 0.98 Most microbes only grow well at water activities of 0.98 or higher.

One would expect to find this protein involved in the elongation of Bacillus anthracis to form its typical shape.

MreB The MreB protein is an actin homologue that forms long filaments to elongate a rod-shaped cell.

Which of the following statements regarding persisters are correct?

Persisters comprise a small minority of a bacterial population. Persisters arise in response to starvation conditions. Persisters are a population's response to preparing for future adverse environmental conditions.

DNA replication does not require a template. (T/F)

false

Microbes will only grow until the least represented (limiting) nutrient in the medium is used up. (T/F)

true

An open system in which the flow rate of a medium through the vessel is automatically regulated to maintain a predetermined cell density is called a ______

turbidostat A turbidostat maintains a certain turbidity that corresponds to a maximum growth rate.

What are the mechanisms that halophiles typically employ to grow in habitats with high concentrations of salt?

Increase the internal concentration of organic molecules such as choline Maintain high levels of potassium chloride and other inorganic solutes

Select all that apply to the structure and function of the FtsZ protein with reference to bacterial cytokinesis.

It is similar to the structure and function of eukaryotic tubulin It is the major component of the Z ring in bacteria It plays a role in the invagination of the bacterial plasma membrane to split a dividing cell

The archaeon Sulfolobus has aspects of its cell cycle that resemble eukaryotes and other aspects that resemble bacteria. Drag each characteristic to the appropriate box.

Like eukaryotes: replicate DNA polymerases cytokinesis multiple origin of replication Like bacteria: chromosome segregation

Every organism has a characteristic minimum, maximum, and optimum growth temperature, as illustrated. To determine the optimum growth temperature for a new isolate, you would perform which of the following?

Measure the generation time at a variety of temperatures, convert the values to growth rate, and plot growth versus temperature

Many foodborne pathogens are controlled by preservation processes that render the food unsuitable to support the growth of microbes. Match each food preservation technique with the environmental factor that is altered.

Vacuum packaging: oxygen concentration Freezing: temperature Pickling: pH Dehydration: water activity

DNA replication in bacteria begins at _________

a single origin and proceeds in both directions

Determine which statement describes what is growing on the plate shown here after membrane filtration.

...

Approximately what percentage of microorganisms can be cultured in the laboratory?

1%

A common concern for beer brewers making sour beers is contamination from Acetobacter. This organism converts ethanol to acetic acid and gives the finished product an undesirable vinegar flavor. Which of the following media would serve as a good enrichment medium to detect the presence of Acetobacter in a brewery environment?

Ethanol, ammonium chloride, phosphate buffer, magnesium sulfate, calcium chloride, trace elements

Which of the following statements regarding the cytoskeletal protein FtsZ are correct?

FtsZ localization determines the site of cell wall growth by recruiting PBPs for peptidoglycan synthesis. FtsZ polymerizes to form the Z ring that determines the site of septum formation.

Match each enzyme to its function to protect a microorganism from toxic forms of oxygen.

Dismutase - superoxide inactivation Peroxidase - utilizes NADH to reduce peroxide Catalase - hydrogen peroxide inactivation

Choose the statement that is not true about the use of colony-forming units as a measurement of bacterial population numbers.

Each cell has enough room and is separated from all others to result in a single colony.

How many generations does it take for a single bacterial cell to become 256?

Eight

A culture in a closed vessel with a single sample of medium where no fresh medium is added and no waste products are removed is called a _________ culture

batch

Assess the following statements and classify them according to whether they describe streak-plate, spread-plate, or a pour-plate protocol.

streak plate: number of organisms is diluted as each sector is inoculated spread plate: after a serial dilution, plates are inoculated with a pipette and a bent metal rod pour plate: after a serial dilution, plates are inoculated by first mixing organisms in liquid agar

After DNA replication two identical DNA molecules are formed. (t/f)

true

As the growth rate constant increases the generation time decreases. (T/F)

true

During cell division, rod-shaped bacteria synthesize new cell wall over the entire surface of the cell. (t/f)

true

High concentrations of sugar or salt are used to control food spoilage because most microorganisms only grow well in habitats with high water activity. (T/F)

true

It is sometimes difficult to obtain pure cultures of microbes that grow naturally in mixed communities. (T/F)

true

The same biofilm may consist of cellulose-degrading bacteria, anaerobic, and aerobic bacteria. (t/f)

true

When counting isolated colonies on an agar plate, it is generally assumed that each colony resulted from one, original cell. (T/F)

true

DNA replication is said to be _______

semiconservative

An example of a protein that mediates the response of many bacteria to starvation is ______

RpoS

In a chemostat, both the microbial population level and the generation time are related to the dilution rate. (T/F)

True

Organisms in the genus Streptomyces can produce and secrete many bioactive compounds, including a diverse array of commercially valuable antibiotics. This bacterial organism is ubiquitous in soil, where it grows as fungal-like hyphae, and reproduces by forming endspores. Although it is widespread, it is not abundant, and therefore isolation of Streptomyces requires enrichment techniques. Rank the following steps in a logical order to isolate Streptomyces from a soil sample.

1. Incubate at high temperature to kill off any non-endspore forming organisms 2. Inoculate medium containing arginine, a preferred carbon and nitrogen source 3. Incubate at 25-30°C to support the growth of Streptomyces 4. Identify Streptomyces by its unique properties: white, raised colonies with an "earthy" odor Incubation at high temperature should be the first step, as this will give the greatest enrichment for Streptomyces, eliminating the vast majority of other soil microbes.

Order the following events as they would occur in a division cycle in Caulobacter crescentus.

1. The origin of replication is duplicated. 2. ParB binds to a parS site near the origin of replication. 3. One ParB/parS complex attaches to a ParA filament. 4. ParA filament depolymerizes and pulls one chromosome toward the opposite pole. 5. Replication of the chromosome is completed.

Examine the various terms used to describe microbial growth requirements by completing each sentence.

An organism that requires high levels of salt is called a halophile An organism able to grow over a wide range of solute concentrations is osmotolerant Optimal growth at a pH above 8 describes a(n) alkalophile Optimal growth at a pH below 5.5 describes a(n) acidophile An organism living under high pressure is called a piezophile An organism that grows best at low water activity is a xerophile

Drag the items to their corresponding class in order to compare the composition of defined and complex media.

Component of defined or complex media -glucose -nano3 -feso4 -citric acid -NaCl Component of complex media only -Tryptone -Peptone -Beef extract -Yeast Extract

Evaluate the statements below and choose those that correctly apply to the hypotheses that account for cell numbers during the death phase and long-term stationary phase of a microbial growth curve.

Microbes can enter a long-term stationary phase if some organisms are able use the metabolic biproducts as fuel Cell death in a batch culture can be attributed to a lack of nutrients and a build up of metabolic waste products that are toxic to the cell The ability of some cultures to enter a long-term stationary phase reflects "survival of the fittest" in a closed system

An Escherichia coli culture you are growing in a lab culture enters the long-term stationary phase of the growth curve. What are the major reasons that scientists believe this occurs?

Nutrients have been depleted and toxins have built up. The population is dominated by viable but nonculturable cells. Programmed cell death is occurring within some members of the population to preserve survivors.

For each situation described, match the microbe with the best enumeration technique for its growth habit.

Petroff-Hausser Counting Chamber - A green alga, Nannochloropsis, grows well in liquid medium, but there is no known solid medium to support its growth. Absorbance - Streptomyces grows as hyphae, long filaments that increase in size, not number. Plate count - Lactobacillus converts milk to yogurt, but will only grow on solid media under anaerobic conditions. Lactobacillus is the only one of these three that can grow well on solid media (under anaerobic conditions) and can produce a colony from a single cell. Although Streptomyces can grow on solid media, a colony develops from fragments of hyphae, so that it can't be enumerated this way. Streptomyces cell mass will scatter light, so absorbance is the best method for this organism. Nannochloropsis cannot be enumerated on plates, and the Petroff-Hausser counting chamber is the best method for its enumeration.

Which of the following are adaptations used by thermophiles to survive in high temperature environments?

Polypeptides are enriched in amino acids like proline that limit their flexibility. The enzyme reverse DNA gyrase alters the supercoiling in the chromosome. Membrane lipids are higher molecular weight, more branched, and more saturated.

Think about the properties of microbes growing in an oligotrophic environment. Cells in which of the stages of the typical bacterial growth curve most resemble cells growing in an oligotrophic environment?

Stationary phase

Which scenarios describe quorum sensing?

Streptococcus pneumoniae cells produce a protein that causes cells to transform into pathogenic forms when the population is large enough. Vibrio fishcheri produces a small protein to control population bioluminescence. Pseudomonas aeruginosa produces a signal molecule to control toxin production.

The site of septum formation in E. coli is determined by the MinCDE proteins. Which of the following statements regarding the positioning of the septum are correct?

The concentration of MinCDE proteins is lowest in the midpoint of the cell

Which of the following statements regarding chromosome partitioning are correct?

The depolymerization of ParA filaments moves a daughter chromosome to a cell pole. parS is a site on the bacterial chromosome.

Examine the ways in which growth is measured in microbial cultures by completing each sentence.

The most obvious way to measure microbial numbers is using a microscope for direct counts. A special slide called a Petroff-Hauser counting chamber is used to count cells in a known volume of culture. Cells can be stained and then counted by interrupting a laser beam as they pass through a flow cytometer Another machine for counting cells, the Coulter counter, detects when cells moving through a pore change electrical currents. Viable counting methods often use plate counts where diluted cultures are spread on the surface of agar plates. Cells from very dilute samples are often concentrated by filtration before plating. Each cell spread on the plates that produces a colony is counted and the number reported as colony forming units. A simple but indirect assay of culture density uses a spectrophotometer to measure turbidity.

In which of the following aspects of the cell cycle is Sulfolobus similar to eukaryotes?

There is an extended G2 phase before segregation of the daughter chromosomes Cytokinesis using proteins in the ESCRT family Conserved replicative DNA polymerases

Thioglycollate medium is used to assess the oxygen tolerance of microbes, as illustrated in the diagram. Examine the "recipe" for this medium, below, and classify this medium by choosing as many of the descriptions that apply.

Thioglycollate medium (per liter): 15 grams peptone 5 grams yeast extract 5.5 grams glucose 2.5 grams NaCl 0.5 gram sodium thioglycollate 1 mg resazurin (color indicator dye) 750 mg agar Complex medium Differential medium

An open system in which a medium containing an essential nutrient is fed into the culture vessel at the same rate as the medium containing microorganisms is removed is called a _____

chemostat

In industry, microorganisms are often cultured in an environment where ideal conditions are maintained through continual nutrient provision and waste renewal. Such a system is called a ______

continuous culture

The structure that divides the bacterial cell in two is termed the ________

cross septum

Some microorganisms use this enzyme to catalyze the breakdown of superoxide to form water and hydrogen peroxide.

dismutase

The genetic material in bacteria is _________.

double-stranded DNA

Semiconservative replication of DNA means ______

each DNA made contains one old strand and one new strand of DNA

Match each culture nutrient level or condition with the bacterial growth phase that would be expected with each condition.

exponential: Nutrients plentiful, bacteria dividing at highest rate lag: Nutrients leveling off, toxins/waste products accumulating death: Nutrients depleted, toxins/waste products high long-term stationary: Nutrients plentiful, bacteria adjusting to new conditions stationary: Nutrients depleted, waves of genetic variants succeed in population

Growth within a biofilm is uniform. (t/f)

false

One DNA strand is used as the template to make two new strands of DNA. (T/F)

false

The bacterial chromosome is linear. (T/F)

false

Microorganisms that are difficult to grow in the laboratory because they have complex nutritional requirements are typically called _______

fastidious

Initial attachment of microorganisms often involves _______

flagella and is reversible

When a broth culture of Bacillus begins to run out of nutrients, the cells ______

form endospores

In a chemostat, the addition of nutrients provides energy for the microbes in culture. When nutrients are limiting, microbes first use the available energy for _________ then as nutrients increase they use the additional available energy for _________.

maintenance; reproduction Energy is first used for maintenance. Excess nutrients will supply the energy for reproduction.

Pelagibacter ubique is a prominent species of bacteria that are free floating in the oceans of the world; as free-floaters they are ____

planktonic

Neutrophiles typically maintain pH homeostasis by exchanging this ion for protons in an antiport system.

potassium

Match each application with the best technique to accomplish the stated goal.

pour plate - Identify aerobes and microaerophiles in an apple cider sample. streak plate - Generate a pure culture from a urine sample. spread plate - Enumerate the microbes in a raw milk sample.

Microorganisms living within biofilms typically use molecular signals to communicate with each to regulate density-dependent growth; this is commonly referred to as _______ ______

quorum sensing