Chapter 7
xerophile
An organism that grows best at low water activity is a __________________.
halophile
An organism that requires high levels of salt is called a ________________.
Coulter counter
Another machine for counting cells, the _________________, detects when cells moving through a pore change electrical currents.
The actin-like protein that seems to be involved in determining cell shape is _________.
MreB
Determine which statement describes what is growing on the plate shown here after membrane filtration.
Only the microbes too large to make it through the filter are grown on the agar plate
alkalophile
Optimal growth at a pH above 8 describes a(n) _______________.
acidophile
Optimal growth at a pH below 5.5 describes a(n) ________________.
How is budding of bacteria to produce daughter cells different from binary fission?
The cytoplasmic division is unequal
direct
The most obvious way to measure microbial numbers is using a microscope for ________ counts.
A microbiologist is attempting to determine the size of a microbial population and has employed several methods. She noticed that the direct count she obtained using a counting chamber and microscope was much higher than her estimate from doing a viable plate count. This discrepancy was encountered during multiple trials. What is the most likely reason for the discrepancy?
The organisms were not readily cultured on the viable count, either because many were dead or because the medium and growth conditions used for the viable count will not support the growth of the microorganism.
What is the result of successful communication between rhizobia and their plant hosts?
The rhizobia invade the plant root and begin to fix nitrogen with the assistance of the plant.
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
Organisms that are not drastically affected by increased pressure are called _________.
barotolerant
Most bacterial and archaeal cells divide by _________.
binary fission
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
When counting colonies on an agar plate, it is generally assumed that each colony resulted from one, original cell.
true
turbidity
A simple but indirect assay of culture density uses a spectrophotometer to measure ______________.
Petroff-Hauser
A special slide called a ______________ counting chamber is used to count cells in a known volume of culture.
lag phase
Adjustment period during which cells are not dividing, but are metabolically active as they adjust to growth conditions
Quorum sensing ________.
All of the choices are correct.
Which of the following can be used to isolate pure cultures of bacteria from mixtures?
All of the choices are correct.
Which of the following is considered a cardinal growth temperature?
All of these are considered cardinal growth temperatures.
Which of the following is a reason for the occurrence of a lag phase in a bacterial growth curve?
All of these are potential reasons.
osmotolerant
An organism able to grow over a wide range of solute concentrations is ________________.
piezophile
An organism living under high pressure is called a __________________.
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.
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 rate versus temperature
Which of these methods can be used to determine the number of viable microorganisms in a sample?
Measuring colony forming units per ml
A microbiologist is testing the drinking water for a municipality. What would be the best method for testing the purified water?
Membrane filtration
death phase
Nutrient depletion and waste accumulation prevent cell growth and cells die exponentially
Which of the following statements regarding persisters are correct?
Persisters comprise a small minority of a bacterial population. Persisters are a population's response to preparing for future adverse environmental conditions.
expontential/log phase
Phase during which cells are growing very quickly, at their maximum rate of cell division
stationary phase
Phase during which nutrient depletion and accumulation of wastes begin to slow cell growth such that the rate of cell division equals the rate of cell death
long-term stationary phase
Phase during which the population evolves to produce successive waves of genetic variants
Which of the following methods could be used to detect the presence of viable but nonculturable cells of a pathogen in a water or food specimen?
Polymerase chain reaction
Bacteria exhibit diverse reproductive strategies. Which of the following are common themes in bacterial cell division?
Replication of the genome. Segregation of the daughter genomes. Each nucleoid is enclosed in a plasma membrane.
Assess the following statements and classify them according to whether they describe streak-plate, spread-plate, or a pour-plate protocol.
Streak- number of organisms is diluted as each sector is inoculated spread- after a serial dilution, plates are inoculated with a pipette and a bent metal rod pour- after a serial dilution plates are inoculated by first mixing organisms in liquid agar
Which of the following is the correct order for binary fission?
The cell elongates, replicates its chromosome, and separates the chromosome into the two parts of the cell, and a septum forms at midcell.
Organisms that require increased pressure for optimum growth are called _________.
barophilic
Organisms that grow near deep-sea volcanic vents are likely to be _________.
barophilic or barotolerant
A culture in a closed vessel to which no additional medium is added and from which no waste products are removed is called a __________ culture.
batch
An open system in which the growth rate is maintained by adding a nutrient (present in limiting quantities) at the same rate that medium containing microorganisms is removed is called a _________.
chemostat
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
Media containing some ingredients of unknown chemical composition are called __________ media.
complex
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.
complex and differential medium
A culture system with constant environmental conditions maintained through continual provision of nutrient and removal of wastes is called __________ culture system.
continuous
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
Media in which all components and their concentration are known are called __________ media.
defined
Drag the items to their corresponding class in order to compare the composition of defined and complex media.
defined or complex- NaNO3, citric acid, glucose, NaCl, FeSO4 complex only- yeast extract, beef extract, peptone, tryptone
A growth medium that distinguishes among different groups of bacteria on the basis of their biological characteristics is called a __________ medium.
differential
In a continuous culture system, the rate at which media is added and removed is called the __________ rate.
dilution
The total number of viable microorganisms remains constant in stationary phase because _________.
either there is a balance between cell division and cell death or there is a cessation of cell division even though the cells may remain metabolically active
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.
eukaryotes- replicative DNA polymerases, mulitple origins or replication, cytokinesis bacteria- chromsome segregation
Microorganisms are at their most uniform in terms of chemical and physiological properties during __________ phase.
exponential
Organisms that do not require oxygen for growth but grow better in its presence are called _________.
facultative anaerobes
Facultative anaerobes differ from aerotolerant anaerobes in that __________.
facultative anaerobes synthesize both superoxide dismutase and catalase for protection against reactive oxygen species (ROS), whereas aerotolerant anaerobes synthesize superoxide dismutase only, allowing survival in the presence of ROS, but they do not utilize O2 in their metabolic pathways
A given medium can be either selective or differential but not both.
false
A microbial environment containing high nutrient concentrations is called an oligotrophic environment.
false
During the lag phase of microbial growth, the cells are metabolically inactive.
false
Nod factors are produced by legume plant roots to attract rhizobia bacteria.
false
Serial dilutions can be used to estimate the total number of bacterial cells, both living and dead, in a solution.
false
The process of segregating the daughter chromosomes in Sulfolobus is more similar to the process in eukaryotic cells than in bacterial cells.
false
The purpose of the penicillin binding proteins is to link phospholipids together in the cellular membrane.
false
The size and shape of a colony is not useful for identification of a microorganism because most microorganisms produce colonies that are indistinguishable from one another.
false
Membranes of thermophilic bacteria are stabilized by phospholipids with _________.
fatty acids that tend to be more saturated
Bacteria reproductive strategies include all of the following EXCEPT _________.
fusion of two bacterial cells that then split into four uninucleate cells
Agar is an excellent solidifying agent for microbiological media because _________.
it is not degraded by most microorganisms and solid agar remains solid until the temperature is raised to 90°C, and liquid agar remains liquid if the temperature is lowered to 45°C
Organisms that are damaged by the normal atmospheric levels of oxygen (20%) but require oxygen at levels of 2-10% for growth are called _________.
microaerophiles
Most known microorganisms maintain their internal pH _________.
near neutral (pH 7)
The site at which replication of DNA starts in bacterial cells is known as the __________.
origin of replication
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.
Organisms that grow well at 0°C and have optimum growth temperatures of 15°C or lower are called _________.
psychrophiles
The __________ is a group of proteins needed for DNA synthesis that assembles at the origin of replication.
replisome
A growth medium that favors the growth of some microorganisms but inhibits the growth of other microorganisms is a __________ medium.
selective
The process of forming a cross wall between two daughter cells is known as __________.
septation
Which type of lifestyle is demonstrated by bacteria in biofilms?
sessile
All of the following are characteristics of spread plates except _________.
spread plates readily grow anaerobic bacteria
Aerotolerant anaerobes __________.
synthesize superoxide dismutase, but not catalase
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.
temperature-freezing oxygen concentration- vacuum packaging pH- pickling water activity- dehydration
The limitation on microbial growth rate at high nutrient levels is/are _________.
the saturation of the transport proteins for nutrient uptake
Organisms that grow near deep-sea volcanic vents are likely to be _________.
thermophilic
A common type of autoinducer found in Gram-negative bacteria are acyl homoserine lactones (AHL).
true
All of the colonies form on the surface of a spread plate, whereas on a pour plate, colonies may be embedded in the agar as well as on the surface.
true
As the growth rate constant increases the generation time decreases.
true
Blood agar is both a differential and enriched medium.
true
During the cell division process, Sulfolobus segregates its chromosomes in a manner similar to bacteria, and performs cytokinesis in a manner similar to that of eukaryotes.
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.
true
In a chemostat, both the microbial population level and the generation time are related to the dilution rate.
true
Membranes of some thermophilic Archaea are stabilized by ether linked phospholipids.
true
Microbes will only grow until the least represented (limiting) nutrient in the medium is used up.
true
Obligate anaerobes are usually poisoned by molecular oxygen but may grow in aerobic habitats if associated with facultative anaerobes that use up all available oxygen.
true
One of the major advantages of a continuous culture system is that the cells can be maintained in the exponential growth phase for extended periods of time.
true
When a young, vigorously growing culture of bacteria is transferred to fresh medium of the same composition, the lag phase is usually short or absent.
true
While establishing a symbiotic relationship, plant hosts communicate with bacteria via secretion of flavonoids and bacteria release Nod factors to communicate with the plant.
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
An open system in which the growth rate is maintained by the removal and addition of media at such a rate as to maintain a constant cell density is called a _________.
turbidostat
The membranes of psychrophilic bacteria have relatively high levels of __________ fatty acids, which allow them to remain semifluid at cold temperatures.
unsaturated
One hypothesis about the decline in cell numbers during death phase is that the cells aren't all dying but instead remain alive but unable to grow when cultured, at least temporarily. These are known as _________.
viable but nonculturable cells
Organisms that grow in mud under relatively nonturbulent bodies of water are likely to be _________.
anaerobes
Which of the following do airborne microorganisms and microorganisms on light-exposed surfaces use to protect themselves from photooxidation?
Carotenoid pigments
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.
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. A decline in cell number during the death phase is observed with cells grown in a batch culture. The ability of some cultures to enter a long-term stationary phase reflects "survival of the fittest" in a closed system. Microbes can enter a long term stationary phase if some organisms are able use the metabolic biproducts as fuel
flow cytometer
Cells can be stained and then counted by interrupting a laser beam as they pass through a ______________________.
filtration
Cells from very dilute samples are often concentrated by _____________ before plating.
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.
colony forming units.
Each cell spread on the plates that produces a colony is counted and the number reported as ______________
A microbiologist is trying to isolate a pathogen expected to be present in very small numbers from a stool specimen in which there are abundant normal microbiota. Which strategy would most likely accomplish this purpose?
Enrichment culture followed by culture on selective agar
All fastidious microorganisms require which of the following for growth?
Extra nutrients (such as whole blood)
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
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.
In which way is the cell cycle of the archaeon Sulfolobus similar to the bacterial cell cycle?
Homologous proteins for DNA segregation
Why is agar a good solidifying agent for media supporting bacteria?
It can be utilized at a variety of temperatures and Most microorganisms cannot degrade it
Which of the following statements support the conclusion that the Sulfolobus cell cycle may not be universal among the Archaea?
Many archaeal genomes encode an FtsZ homologue and The SegAB system for chromosome segregation is only found in Sulfolobus and some members of the Euryarchaeota.
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
How is the cell cycle of Sulfolobus spp. similar to that of eukaryotes?
The cytokinesis process in Sulfolobus is similar to the process in eukaryotes.
Which of the following might be missed if viable counts are done on food and/or water specimens?
Viable but nonculturable cells
plate counts
Viable counting methods often use __________ where diluted cultures are spread on the surface of agar plates.
Explain why a scientist would need to increase the dilution rate in a chemostat from 0.20 hr-1 to 0.50 hr-1.
When the dilution rate is low, the availability of an essential nutrient is limited, creating an environment where the organism can expend energy on survival only, not growth and reproduction. Increasing the dilution rate enables an increase in cell density.
most probable number
While plating techniques are valuable, another viable counting method, ___________________ analysis, can be used when cells can not be cultured on solid media.
During cytokinesis, a critical step in septation is the assembly of the _________.
Z ring
Organisms that ignore oxygen and grow equally well in its presence or absence are called _________.
aerotolerant
The length of the lag phase of growth can vary depending on _________.
all of the choices are correct
Which of the following are a reason(s) for the decline in cell numbers during the death phase?
all of the choices are correct
Which of the following strategies enable non-acidophilic bacteria to endure lower pH environments?
all of the choices are correct