Micro HW2

1. Decontamination 2. Disinfection 3. Preservation 4. Sterilization

1. Mechanical removal of most microbes from living or inanimate surfaces 2. Reduction of most microbial life on inanimate surfaces 3. Slows microbial growth but does not reduce the number of existing microbes. 4. Destruction of all microbial life

The generation time of Mycobacterium tuberculosis is

12

The generation time of Mycobacterium tuberculosis is

12 hours.

Consider a culture of Staphylococcus aureus growing in exponential phase with a generation time of 30 minutes. Beginning with 2 x 105 cells per ml, how long will it take the culture to reach a density of approximately 1.3 x 107 cells per ml?

3 hours We know the population of cells will double every 30 minutes. One way to solve this problem is with the formula Nt = N0 x 2n, where Nt is the number of cells at a given time (in minutes), N0 is the initial number of cells, and n is the number of generations. In this question, Nt = 1.3 x 107 cells/ml, N0 = 2 x 105 cells/ml, and we need to solve for the number of generations. This gives us 1.3 x 107 cells/ml = 2 x 105 cells/ml x 2n, or 2n = (1.3 x 107 / 2 x 105), or 2n = 65, or n = 6 generations. Since the generation time is 30 minutes, after 6 generations, 3 hours will have elapsed. Note that because the original question gave us an approximate number of cells (Nt = 1.3 x 107 cells/ml instead of Nt = 1.28 x 107 cells/ml), the numbers are rounded off slightly in these calculations. If you don't remember how to set up the formula, all is not lost! You could still solve this question by working your way through the example, since it doesn't involve too many generations. Starting with 2 x 105 cells/ml, you know that 30 minutes later you'll have twice this many, or 4 x 105 cells/ml. After an hour, you'll have twice this, or 8 x 105 cells/ml. After 1.5 hours, you'll have twice this number, or 1.6 x 106 cells/ml. After two hours, you'll have 3.2 x 106 cells/ml. After 2.5 hours, you'll have 6.4 x 106 cells/ml, and after three hours, you'll have 1.28 x 107 cells/ml, or the approximately 1.3 x 107 cells/ml in the question.

Prokaryote Ribosomes

50S + 30S -> 70S

Eukaryote Ribosomes

60S + 40S -> 80S

Starting from a single bacterium, after six generations of binary fission, how many bacterial cells will be present?

64

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

8

Consider a culture of E. coli growing in exponential phase with a generation time of 20 minutes. Beginning with 2 x 106 cells per ml, how long will it take the culture to reach a density of about 3.2 x 107 cells per ml?

80 minutes We know the population of cells will double every 20 minutes. One way to solve this problem is with the formula Nt = N0 x 2n, where Nt is the number of cells at a given time (in minutes), N0 is the initial number of cells, and n is the number of generations. In this question, Nt = 3.2 x 107 cells/ml, N0 = 2 x 106 cells/ml, and we need to solve for the number of generations. This gives us 3.2 x 107 cells/ml = 2 x 106 cells/ml x 2n, or 2n = (3.2 x 107 / 2 x 106), or 2n = 16, or n = 4 generations. Since the generation time is 20 minutes, after 4 generations, 80 minutes will have elapsed. If you don't remember how to set up the formula, all is not lost! You could still solve this question by working your way through the example, since it doesn't involve too many generations. Starting with 2 x 106 cells/ml, you know that 20 minutes later you'll have twice this many, or 4 x 106 cells/ml. After 40 minutes, you'll have twice this, or 8 x 106 cells/ml. After 60 minutes, you'll have twice this number, or 1.6 x 107 cells/ml. And after a final doubling, or 80 total minutes, you'll arrive at 3.2 x 107 cells/ml, the number given in the question. See section 4.1 in the text for more information.

From which of the following would you be most likely to obtain a pure culture?

A single colony on a streak plate

You use the streak-plate method to obtain a pure culture and observe individual colonies following incubation. Consider a single bacterial colony. All of the following statements about the colony are true EXCEPT:

All cells in the colony are expressing the same set of genes and are performing the same metabolic functions.

Cryptosporidium infection results in diarrhea that is self-limiting in healthy individuals, but in ______ patients, it can produce dehydration through severe diarrhea and can be life-threatening.

All of these

The presence of microbes in food can be:

All of these

How common are food spoilage microorganisms?

Almost all of our foods contain them.

Which of the following are examples of growth factors?

Amino acids Vitamins Nucleotides

According to the graph, what is the impact of cold temperatures on E. coli?

As temperatures decrease, the growth rate decreases

Aerobe

Benchtop

Capnophile

Candle jar

Exponential/Log phase

Cells are actively growing, doubling the population with each generation

Lag phase

Cells are not dividing but are synthesizing enzymes required for growth

What happens to bacterial cells when their maximum growth temperature is exceeded?

Cells begin to die when their maximum growth temperature is exceeded.

What food item is least likely to contain viable vegetative pathogens?

Chicken cooked to 170 degrees F

Location for the cellular process of photosynthesis.

Chloroplast

Which of the following are considered trace elements that are required in such small amounts that most natural environments, including water, have sufficient levels to support microbial growth?

Cobalt Copper Molybdenum Manganese

What organism was the cause of the outbreak at the Seneca Lake Sprayground?

Cryptosporidium

Which of the following are examples of biofilms? Choose all that apply.

Dental plaque Scum accumulating in toilet bowls Slipperiness on rocks in stream beds

Death phase

Due to nutrient depletion and waste accumulation, cells begin to die at an exponential rate

Location for protein synthesis and some protein modifications.

Endoplasmic reticulum

In eukaryotes, proteins destined for secretion contain a signal sequence that will cause ribosomes to dock onto which of the following cellular structures?

Endoplasmic reticulum.

Which of the following is found exclusively in prokaryotic cells?

Endospore

Both human and bacterial cells divide by mitosis.

False

Cell division is triggered exclusively when cells attain a threshold mass.

False

Cells cannot begin a new round of replication until they have completely finished dividing.

False

DNA helicase is responsible for adding nucleotides to the growing end of the DNA.

False

True or false: Cells can replicate and transcribe DNA that contains thymine dimers.

False

True or false: Chlorine treatment is effective in removing Cryptosporidium from water.

False

Microaerophile

Gastight container with chemical pack that reduces oxygen to 5-15%

Obligate anerobe

Gastight container with chemical pack that reduces oxygen to ~0%

On which of the following plates do you predict E. coli would grow the most slowly?

Glucose-salts agar

Location for protein modification prior to secretion or delivery to other cellular compartments.

Golgi apparatus

Microtubule

Involved in the movement of chromosomes during cell division.

UV irradiation inactivates Cryptosporidium because:

It blocks the action of DNA polymerase and RNA polymerase

Location for storage of many types of degradative enzymes

Lysosomes

Which of the following are found exclusively in eukaryotic cells?

Lysosomes, Golgi apparatus, Mitochondria, Endoplasmic reticulum

Location for most metabolic reactions in cellular respiration.

Mitochondria

Intermediate filament

Mostly responsible for mechanical support and helps the cell resist physical stress.

Which of the following are considered the major elements that primarily make up components of cells in microorganisms and all living things?

Nitrogen Phosphorus Sulfur Carbon Oxygen Hydrogen Potassium Magnesium Calcium Iron

Location for DNA, and for RNA synthesis.

Nucleus

You observe bacteria growing on the surface of a Petri dish of nutrient agar you left on the counter in your lab. You can be confident that your bacteria are NOT which of the following?

Obligate anaerobes

_________ is a brief heat treatment that reduces the number of spoilage organisms and destroys pathogens. It can be used on foods or inanimate objects.

Pasteurization

Location for storage of protective compounds that break down lipids and detoxify certain chemicals.

Peroxisomes

During a one hour time period in a population of approximately a billion cells, ten cells divide, and a hundred thousand cells die. This pattern suggests the population is experiencing which phase of a growth curve?

Phase of prolonged decline

Following treatment with alum (aluminum sulfate), what can you conclude about Greenlake?

Phosphorus became a limiting nutrient. Correct! Alum works by removing phosphorus from the water, making it a limiting nutrient. Because cyanobacteria can fix both carbon dioxide and nitrogen that are readily available from the atmosphere, those nutrients are not limiting. However, limiting the availability of phosphorus helps control the cyanobacterial blooms

Anabaena is a genus of filamentous cyanobacteria commonly found in aquatic environments, where it harvests energy from sunlight and fixes both carbon dioxide and nitrogen. Knowing this, how would you classify Anabaena?

Photoautotroph

How would you classify the cyanobacteria from Greenlake in terms of their carbon and energy sources?

Photoautotroph Microbiologists commonly classify microorganisms by their sources of energy and carbon. Remember that a chemolithoautotroph obtains its energy from inorganic sources and fixes its carbon from inorganic compounds like carbon dioxide. Cyanobacteria obtain their energy from sunlight and fixes carbon from carbon dioxide, making them photoautotrophs. See section 4.5 in the textbook for more information.

What type of organism caused the outbreak at Seneca Lake Sprayground?

Protozoan

How would you classify L. methylaminiphilus with regards to temperature requirements?

Psychrotroph

Which enzyme is NOT involved in DNA replication?

RNA polymerase

When studying microbes, why is it important to separate mixed communities into individual pure cultures of the different species?

So we can understand the biochemical characteristics of one species without confusing it with another species.

During which stage of growth does cell division equal the rate of cell death?

Stationary phase

Which of the following environmental factors is the most important in influencing the growth rate of bacteria?

Temperature

You inoculate a flask containing a complex medium with a culture of bacteria and use a spectrophotometer to measure the absorbance of the culture to detect growth. Initial measurements show a modest turbidity that remains unchanged for the first few hours, followed by a steady increase for the rest of the day. Why was there this delay in growth following inoculation?

The bacteria were actively expressing genes and synthesizing enzymes in order to grow in their new environment.

Cryptosporidium was not susceptible to disinfection through filtration and chlorination of the spray park's water supply.

True

Environmental factors control microbial growth through their influence on enzyme activity.

True

It is sometimes difficult to obtain pure cultures of microbes that grow naturally in mixed communities.

True

Microbes will only grow until the least represented (limiting) nutrient is used up.

True

Rod-shaped bacteria such as Escherichia coli, Salmonella, and Bacillus species synthesize new cell walls over the entire surface of the cell.

True

Sterilization is the destruction of all living microbes from a surface by physical or chemical means.

True Sterilization also includes destruction of all viruses/endospores from a surface. While endospores are alive, viruses technically are not.

Actin filament

Typically functions to allow the cell cytoplasm to move.

What type of radiation in sunlight causes damage to DNA?

UV radiation

Which of the following is a method of choice for achieving a sufficient level of microbial control in routine day to day situations?

Washing and scrubbing with soaps and detergents.

What was the most likely mode of transmission of Cryptosporidium at the Seneca Lake State Park Sprayground?

Water-borne

Phosphate is typically a limiting nutrient in waterways. Phosphate was historically widely used in detergents, but because wastewater treatment plants do not fully remove phosphate before discharging their treated water, it has been mostly removed from these detergents in order to protect our waterways. Some complain that modern detergents do not clean as well following this change. Predict what would happen if phosphate was returned to detergents.

We would experience blooms of cyanobacteria and algae in our waterways.

Stationary phase

With nutrients depleted, total number of viable cells remains constant, with some dying while others multiply

Following the Exxon Valdez oil spill, beaches in Prince William Sound were treated with nitrogen compounds in order to enhance the bioremediation of the oil. What does this tell you about the ecosystem of these beaches?

With the arrival of large quantities of hydrocarbons, nitrogen was a limiting nutrient for microbial growth.

A single species of bacteria grows best at:

a modest range around an optimum temperature.

UV water treatment systems are effective in treating:

all of these

The most common organisms causing food spoilage are:

bacteria, yeasts, and molds.

Most cultured bacteria tend to multiply by:

binary fission

UV light causes _____ bonds to form between adjacent thymines on the same strand of DNA.

covalent

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

cross septum.

You have a culture of bacteria in which cells are dying off at a constant rate. This culture is most likely in _________ phase.

death

By keeping food cold, the growth rate of food spoilage microorganisms is

decreased.

Chlorine has traditionally been used to disinfect water, preventing the spread of waterborne illnesses. However, chlorine (and other disinfectants) can react with naturally occurring water chemicals, forming _______, which can have long-term health risks.

disinfection by-products (DBPs)

Microorganisms that have complicated nutritional requirements are

fastidious. Correct! Microorganisms that are fastidious are less resourceful metabolically, and as a result they require numerous growth factors including vitamins and amino acids in order to grow. This typically makes them more difficult to culture in a laboratory. See section 4.5 in the text for more information.

Most bacteria reproduce by ______.

fission

Production of extracellular polymeric substances (EPS) enables bacteria to

form biofilms. Correct! Bacteria frequently grow in polymer-encased communities called biofilms. These involve the production and release of polysaccharides, DNA, and other hydrophilic polymers, yielding a slimy, mesh-like accumulation of polymers refered to as extracellular polymeric substances, or EPS.

You have a culture of bacteria in which cells are actively expressing genes and synthesizing enzymes, but cells are not dividing. This culture is most likely in _________ phase.

lag

Photolyase is an enzyme that cells use to repair thymine dimers in a ____-dependent manner.

light

During which phase of growth do researchers measure the generation time of a culture of bacteria?

log

A eukaryotic cell that is involved in synthesizing large amounts of protein might be expected to have

many ribosomes. many mitochondria. a lot of rough endoplasmic reticulum.

Excision repair, which is also used to correct thymine dimers, requires:

none of these

An enclosed compartment filled with an inert gas such as nitrogen would be most appropriate for growing __________.

obligate anaerobes

During phagocytosis, cellular membrane projections will "wrap around" a target. What are these cellular projections called?

pseudopods

Cells must ______ their DNA prior to cell division.

replicate

The FtsZ protein is needed to form the _____.

septum

In the U.S., the CDC estimates that ___ people suffer each year from some form of foodborne infection.

several million

The energy source for contraction of the FtsZ ring during cell division comes from _____.

the hydrolysis of GTP

The type of foodborne infection known as an intoxication is caused by:

toxins produced by microbes as they grow in the food.