Microbiology Exam 2

All purple questions

DO inorganic compounds provide as much energy for bacteria as organic compounds? Explain! 

They provide considerably less energy than organic compounds because they tend to have less electrons and a more positive reduction potentials.

HOW does the process of generating energy from inorganic compounds differ from that of organic compounds? What are the similarities? Explain! 

• no glycolysis or citric acid cycle

• when electrons from inorganic compounds are passed to transmembrane proteins in the ETC, a PMF is generated, and ATP is generated by chemiosmosis. 

• Fewer steps because less energy is released, process doesn’t need as many steps

• Similar with usage of ETC, the creation of a PMF, and generation of ATP through chemiosmosis. 

WHAT are advantages and disadvantages to using hydrogen as an electron source? WHY are most of these bacteria anaerobic? 

• Advantages: very negative reduction potential

• Disadvantages: only has a single electron to donate, can only make 1 ATP

• Most organisms that use it as an energy source are anaerobic because H2 levels are unstable in oxygenated environments.

WHAT is acetogenesis? What are the two different groups of bacteria that carry out this process? Where would you find these bacteria?

• Acetogenesis is the process of anaerobic respiration when hydrogen is used as the electron donor and CO2 is used as the electron acceptor.

• Homoacetogens convert CO2 into acetate.

• Methanogens convert CO2 into methane.

• They are found in the stomachs of ruminants (cows, sheep, etc.), in anaerobic marshland mud, and swamps.

• They are often responsible for the smell coming from those areas!

WHAT are advantages and disadvantages to using sulfur compounds as an electron source? Why do many of these bacteria live in acidic environments? 

Advantages:

• they have the most negative reduction potentials

• wide range of oxidation states that allows microbes to use it as an energy source for chemosynthesis

Disadvantages:

• produce less energy

Why acidic env?

• Hydrogen ions are often produced from sulfur oxidation, which lowers the pH of the surrounding environment → many sulfur oxidizers are adapted to living in low pH environments

WHAT is reverse electron flow? WHICH bacteria need to use this? 

• reverse electron flow is when a microbe is using an electron donor with a more positive reduction potential than NAD

• uses energy from the proton motive force to create enough energy to reduce NAD to NADH.

• sulfur oxidizers and autotrophic bacterium

WHAT are advantages and disadvantages to using iron compounds as an energy source? Explain how these bacteria can be involved in bioremediation. 

Advantages:  

• Fe+2 is one of the most common environmental sources of iron for bacterial metabolism; it has one of the most negative reduction potentials of all iron compounds.

Disadvantages: 

• more positive reduction potentials than sulfur containing compounds

• even shorter electron transport chains

• even less total energy generated

• a requirement for reverse electron flow

Bioremediation:

• Iron compounds are generated from mining waste, so bacteria that use iron as an energy source participate in bioremediation.

WHAT are advantages and disadvantages of using nitrogen compounds as an energy source? WHY are these bacteria bad news for farmers?

Advantages:

• positive reduction potentials – so generally they make better electron acceptors than electron donors.

Disadvantages: 

• low energy production

Why are they bad for farmers?

• one group (nitrifying) oxidizes ammonia (NH4+) to nitrate(NO3-) → NO3- is water soluble and can be washed out with irrigation

• then the second group (denitrifying) oxidizes nitrate to nitrite (NO2) → makes N gaseous and leaves soil

• most plants prefer to use ammonia as a nitrogen source, nitrification is considered harmful to many crops

DO all microbes produce oxygen from photosynthesis? 

No.

WHAT types of microbes are phototrophs? 

• cyanobacteria

• green sulfur bacteria

• algae

• euglena

Without choroplasts, WHERE do bacteria store their photosynthetic pigments? 

• in the cell membrane

• Some use chlorosomes, small membrane compartments just inside the cell membrane that contain the photosynthetic pigments and components to carry out photosynthesis. 

IF you are an autotrophic phototroph, in addition to ATP what do you use the energy from photosynthesis to do? WHY is this important? 

• Autotrophic phototrophs rely on photosynthesis to produce ATP but also to produce energy to reduce NAD to NADH for carbon fixation. 

• carbon fixation is crucial because they rely on CO2 as a carbon source

WHAT is oxygenic photosynthesis? Why is it called that? Where does the electron come from that gets excited by light? Where does that electron end up? How many electron transport chains are there? How is ATP generated? How is NAD reduced to NADH in autotrophs? What is noncyclic photophosphorylation? 

• The energy from light is used to produce ATP and provide energy to reduce NAD to NADH for carbon fixation.

• Oxygen photosynthesis utilizes the Z schemes – two different electron transport chains that increase the amount of energy that can be produced.

• The splitting of water produces an electron (and also oxygen!) that can be activated by light energy to enter the two photosystems

• The ETC’s generate a proton motive force and chemiosmosis is used to created ATP.

• After gaining energy through these systems the electron is eventually used to reduced NAD to NADH.

• Because the electron has a beginning (coming from the splitting of water) and an end (reducing NAD), energy generation in oxygenic photosynthesis is called noncyclic photophosphorylation.

WHAT is anoxygenic photosynthesis? Why is it called that? Where does the electron come from that gets excited by light? Where does that electron end up? How many electron transport chains are there? How is ATP generated? How is NAD reduced to NADH in autotrophs? What is cyclic photophosphorylation? 

• a type of photosynthesis that does not produce oxygen.

• There is a single photosystem that cycles an electron.

• There is still an electron transport chain that generates a proton motive force and uses chemiosmosis to create ATP

• the electron that gets excited by sunlight is in the photosynthetic pigment that gets excited by the light energy

• the electrons that are used to reduce NAD come from inorganic compounds (usually containing sulfur or iron). More (+) RPs than NAD.

• reverse electron flow must be used to generate energy to reduce NAD to NADH for carbon fixation.

• Because the electron that gets excited by light energy in the photosynthetic pigment continues to cycle through the electron transport chain, this type of ATP generation is called cyclic photophosphorylation.

WHAT are similarities between anoxygenic and oxygenic photosynthesis? What are differences?

Similarities

• both use the ETC to generate a proton motive force and chemiosmosis to created ATP

• both use light energy to convert it into chemical energy

Differences

• they differ in electron donors and byproducts

• oxygenic photosynthesis uses O2 as an electron donor

• anoxygenic photosynthesis uses inorganic compounds as an electron donor

WHY does oxygen make the best electron acceptor? 

• high electronegativity

• positive reduction potential

WHY do bacteria create less energy by using non-oxygen e- acceptors? 

Because any electron acceptor has a more negative reduction potential than oxygen, which limits its ability to produce energy

WHY would a bacterium use something other than oxygen as an electron acceptor? 

• Because it’s what’s available

• environmental factors

WHAT are the two different pathways in bacteria that use alternative electron acceptors to generate ATP? 

• anaerobic metabolism + fermentation

• anaerobic respiration

IS carbon dioxide a good electron acceptor? Why or why not? What are the special groups of bacteria that use it as an e- acceptor? 

• CO2 is a common electron acceptor because it is a waste product from chemoorganotrophs (like humans!) and is often readily available in the environment.

• common because it has a relatively positive reduction potential, but it’s less effective than oxygen and produces less energy

• acetogenic bacteria and methanogenic archaea use it as an electron acceptor

WHAT is the difference between assimilative and dissimilative metabolism? Can the same compound be used for both? Explain! 

• dissimilative metabolism: inorganic compounds are used as electron acceptors in order to generate energy for the cell. Once the substance as accepted the electron(s) it is usually secreted from the sole. The only purpose of the substance is to accept electrons.

• In assimilative metabolism, bacteria utilize inorganic compounds (like nitrogen and sulfur containing compounds) as building blocks for macromolecules. These substances do not serve any purpose in generating energy for the cell.

• Can sometimes use the same compound for both.

• e.g. you have a bacterium that uses sulfur as an electron acceptor in anaerobic respiration. When sulfur gets reduce to hydrogen sulfide, the bacterium can use that as a sulfur source for producing amino acids.

IS nitrate a good electron acceptor? What role do denitrifying bacteria play in soil health? Explain! 

• good electron acceptor because of its positive reduction potential (close to oxygen!).

• Denitrifying bacteria use nitrate as an e-acceptor in anaerobic respiration →The products of nitrate reduction are gaseous and remove excess nitrogen from the soil. Since most soils contain an excess of nitrogen (from human use, fertilizer, etc.), this process is helpful in maintaining healthy soil.

ARE sulfur containing compounds good electron acceptors? 

not really, they don’t have great reduction potentials for being accepting electrons, but they can be used by bacteria when nothing else is available.

ARE organic compounds generally better e- donors or e- acceptors? Why? Are they ever acceptors?

• generally better e-donors due to their highly negative reduction potentials. 

• Organic compounds can rarely serve as final electron acceptors in anaerobic respiration, but more often serve as electron acceptors in fermentation pathways that are part of anaerobic metabolism.

WHY is fumarate the most common organic e- acceptor? 

• Fumarate has an almost neutral reduction potential of +0.03, which means that it can accept or donate electrons – depending on the reduction potential of its partner.

• Since the majority of organic compounds have more negative reduction potentials than 0.03, fumarate can serve as an electron acceptor for these compounds.

Other than anaerobic respiration, what is the other way organic compounds can serve as e-acceptors in ATP generation? Explain!

• they can more often serve as electron acceptors in fermentation

• its pathways use organic compounds as both electron donors and acceptors. Since the difference in reduction potentials is so small, energy is not created this way

HOW is ATP made in anaerobic metabolism?

Only glycolysis actually generates ATP

IF fermentation doesn’t produce any ATP, what is its purpose in anerobic metabolism? WHY is this important? 

• fermentation pathway is crucial because it provides a way for reduced NADH to donate e- so that NAD can return to glycolysis and keep that pathway running.

• without glycolysis, no ATP would be produced and the cell would die

IS a lot of ATP produced by anaerobic metabolism? Explain! 

• no.

• only uses glycolysis and fermentation.

• Glycolysis only generates ATP through substrate level phosphorylation, which means not much ATP is generated by these bacteria.

WHAT is fermentation? 

it is a metabolic process that converts sugar into acids, gases, or alcohol in the absence of oxygen.

WHAT are the products of fermentation? HOW do humans take advantage of these products?

• Common byproducts from fermentation pathways include alcohols, acids and gases – sometimes just a single product, sometimes all three!

• Often these products are used by humans to flavor some of their favorite foods and drinks – yogurt, sauerkraut, alcohol, breads, etc.

WHAT is lactic acid fermentation? What type of bacteria use this pathway?

• Lactic acid fermentation is a metabolic process in which glucose (sugar) is converted into lactic acid and energy in the absence of oxygen (anaerobic conditions). 

• performed by Gram positive bacteria.

• Lactic acid is the main product of this pathway and is used to flavor yogurt and sauerkraut.

WHAT is mixed acid fermentation? What type of bacteria use this pathway? 

• The fermentation of glucose produces acetic acid, lactic acid and succinic acid.

• Performed by Gram negative enteric bacteria. Enteric bacteria can be found in the digestive tract of humans and other animals.

• These acids are used in diagnostic tests to detect the presence of these bacteria

HOW is succinate fermentation different from most fermentation pathways? Is more or less energy generated? Explain!

• fermentation pathway that doesn’t use glycolysis to generate energy.

• Not enough energy is produced to establish a proton motive force, so instead, a Na+ ion gradient is established across the cell membrane.

• These bacteria grow very slowly due to low energy production

WHAT is binary fission? HOW long does it take?

• cell division in prokaryotes.

• The fastest bacteria can do this in about 15 minutes

WHY is binary fission simpler than meiosis/mitosis? 

because there is only one chromosome, there is no nucleus and there aren’t other organelles that must be replicated and split between two new daughter cells.

WHAT is generation time? 

Generation time: is the time it takes for one cell to replicate and form two cells.

WHAT four things affect the length of generation time? What are two examples of things that shorten generation time? What are two examples of things that make generation time longer? 

1. size! (smaller bacteria are faster – SA:volume ratio!)

2. nutritional requirements

3. environmental conditions (temperature, pH, osmotic pressure, etc.)

4. being inside or outside a host (pathogens)

• Faster generation time: high SAV ratio, high nutrient availability

• Slower generation time: extreme temperatures, low SAV ratio

HOW do prokaryotes control the steps of binary fission? 

Through various proteins:

• Min

• MinE

• Fts

• Fts Z

• MreB

WHAT are the roles of the Min proteins? What does the MinE protein do and how does it work? 

Min proteins

• signal to the cell when replication of the solitary chromosome is complete

• recruit the Fts proteins to the exact center of the cell and together they form the divisome.

MinE proteins

• oscillates from one end of the cell to the other, spending more time at the poles of the cell than in the center.

• The cell knows where to form the septum and split the cell into two daughter cells by finding the location where there is the least amount of MinE – which will be the exact center of cell.

WHAT are the roles of the Fts proteins? What does the FtsZ protein do and how does it work? 

Fts proteins

• work together with Min proteins to form the ring of proteins called the divisome

• responsible for generating new membrane and cell wall to help the cell elongate.

• Once the cell has completely replicated, the two copies of the chromosome are separated by Fts proteins

Fts Z protein

• is a ring formation at the midpoint of the cell that depolymerizes to pinch off the 2 daughter cells

WHAT is the divisome? WHAT is its function? 

• it’s a ring of proteins (Min and Fts)

• it functions to assemble the division septum and synthesize the new cell wall and membrane material during binary fission

HOW do bacillus-shaped cells maintain their shape during binary fission? Do you think this same process would work for spirillum-shaped cells? Why or why not? Explain! 

• MreB proteins form a sort of cytoskeleton underneath the cell membrane that acts as scaffolding.

• the contact points with the membrane ONLY occur on the long sides of the cell, so this is the only place that new cell wall and cell membrane synthesis take place – ensuring that the new cells will still maintain the bacillus shape.

• There would be a similar process in spirillum, but likely more proteins as it’s a long and curly shape.

WHY do prokaryotes need to be careful when making more cell wall during binary fission? 

the cell wall is the only thing protecting the cell from the environment. with a compramized cell wall, the bacteria is more likely to die. 

WHAT are autolysins? What is there role in binary fission? 

• enzymes that make very small snips in the existing peptidoglycan and new sugars are added to the backbone.

• This has to be done carefully and at many varying points with the cell wall structure so that the overall strength and rigidity of the cell wall is maintained throughout the process.

WHAT is bactoprenol? What is its role in binary fission? 

• a lipid carrier that transports N-acetylglucosamine and N-acetylmuramic acid across the cell membrane

• it’s a lipid so that it can freely diffuse across the membrane

WHAT are glycosylases? What are their role during binary fission? 

enzymes that attach the new sugars to the existing sugar backbone of the peptidoglycan during formation of the new cell wall. 

WHAT are transpeptidases? What are their role during binary fission? 

enzymes that link together the amino acids that make up the side chains on the peptidoglycan. finishing 

WHY are all of the enzymes involved in binary fission great antibiotic targets? Explain!

none of those enzymes or molecules are in eukaryotic cells, meaning the bacteria can be safely killed in a human host

WHAT is a bacterial growth curve? What does it show? 

they track the growth of a bacterial population over time in a closed system.

WHAT are the four phases of a bacterial growth curve? 

1. Lag

2. Log (or exponential)

3. Stationary

4. Death

WHAT happens during lag phase? What are two things that would make this phase longer? What are two things that would make this phase shorter? Explain! 

• the total number of bacteria remain the same, but massive amounts of ATP are used to replicate macromolecules (including DNA) and grow the cell.

• Shorter: warm temperature and high nutrient availability

• Longer: colder temperature and low nutrient availability

WHAT happens during log phase (exponential)? What are two things that would make this phase longer? What are two things that would make this phase shorter? Explain!

• the total number of bacteria increase exponentially.

• Massive amounts of ATP are still being used to replicate macromolecules.

• Generation time is measured during this phase.

• This phase continues until one or more of the following occurs: running out of nutrients, running out of space, toxic byproducts accumulating in the media.

• Longer: high amount of space to cover, high nutrient availability

• Shorter: small amount of space, low nutrient availability

WHAT causes a bacterial population to enter stationary phase? Are new bacterial still created during this phase? Explain! 

• the total number of bacteria stays the same because new bacteria are being created at the same rate as cell death.

• Nutrients, space and/or toxic waste is starting to kill some bacteria.

WHAT is death phase? Does death phase occur as quickly as log phase? Why or why not?

•  all cells in the population are dying. The overall cell number is decreasing.

• Death does not occur at the same rate as log phase, so the slope will be more gradual.

• Death takes longer because bacteria like to try to hold on, possibly forming endospores

WHY do we need to be able to count bacteria? 

• various medical purposes such as determining the extent of an infection

• manufacturing purposes: determining if a food or product is safe to distribute to the public

HOW does total cell count determine the number of bacteria in a sample? What are advantages to this technique? Disadvantages? 

• In a total cell you take a small amount of a broth culture of bacteria or a dried sample of bacteria and place it on a specially marked, gridded slide. Looking through a microscope, you can count the individual bacteria and extrapolate how many bacteria are in the entire sample

Advantages:

• very quick and easy!

• flexible (can use fresh or dried bacterial culture)

Disadvantages:

• not super accurate (using a small sample and extrapolating)

• can’t distinguish living from dead cells

• not great for motile cells

• need a pure culture sample

• cannot be returned to the experiment

HOW does standard plate count determine the number of bacteria in a sample? What are advantages to this technique? Disadvantages? 

In this experiment, a liquid broth culture of bacteria is serially diluted until there are a small enough number of bacteria that they can be plated and grow into individual colonies that will be counted.

Advantages:

• very accurate very sensitive (almost impossible to miss living bacteria)

• only counts living bacteria

• can use many different sample types (because the sample is diluted so many times it doesn’t have to be pure)

Disadvantages:

• very complicated procedure – many spots for mistakes to happen!

• requires lots of equipment and supplies

• takes 24 hours to see results

• can’t return the sample to the experiment

HOW does turbidity determine the number of bacteria in a sample? What are advantages to this technique? Disadvantages? 

when bacteria grow in a liquid culture they cause the media to get cloudy, or turbid. Using a spectrometer, you can determine how many bacteria are in a liquid culture.

Advantages:

• quick and easy

• can return the bacteria to the experiment

Disadvantages:

• bacteria can form clumps that affect the absorbance

• must start with a pure, broth culture

• cannot differentiate between living and dead cells

• not the most accurate

WHICH method would you use if keeping all of the bacteria in the culture was most important? 

• Turbidity

• can return sample to the culture

WHICH method would you use if were starting with a soil sample? 

• Standard plate count because

• it’s highly flexible and doesn’t require a pure culture. 

• the serial dilution step ensures that a variety of samples can be used

WHICH method would you use if you only had a dried sample to work with?

• Total cell count

• would be easiest to place on the gridded slide and count.

WHAT happens to bacteria when temperatures are too hot? Could room temperature be too hot for some bacteria? Explain! 

• membranes lose stability

• enzymes start to fall apart and the inactivation of most macromolecules.

• room temperature could be too hot for obligate psychrophiles. These bacteria can’t survive in temperatures above 60°F.

WHAT happens to bacteria when temperatures are too cold? Could body temperature be too cold for some bacteria? Explain! 

• too cold = rigid membranes, inability to transport substances, non-functional enzymes that can’t move, and thick cytoplasm that blocks movement of macromolecules

• obligate thermophiles live in temperatures close to 140°F and would likely die in body temperatures.  

WHAT temperatures do thermophiles live in? What is the difference between an obligate thermophile and a facultative thermophile? Do you think a pathogen could be an obligate thermophile? Explain! 

• They live at temperatures close to 140°F.

• obligate (they must be in hot temps)

• facultative (they prefer lower temps but can tolerate hot temperatures)

• obligate extremophiles can’t be pathogens bc humans aren’t extreme enough

• Pseudomonas (facultative) can grow in improperly maintained hot tubs and causes rashes for unsuspecting users.

WHAT physiological differences do thermophiles have to allow to survive in hot temperatures? 

• additional ionic bonds to hold proteins together,

• lots of hydrophobic amino acids to resist protein unfolding

• saturated fatty acids in their membranes to prevent them from coming apart

WHAT temperatures to mesophiles live in? Are pathogens likely to be mesophiles? Why or why not? Explain! 

• live between room (70° F) and body (98.6° F) temperatures. The vast majority of pathogens are in this group – like E. coli and S. aureus.

• high chance of pathogens bc that range is within human body temperature. 

WHAT temperatures do psychrophiles live in? What is the difference between an obligate psychrophile and a facultative psychrophile? Do you think a pathogen could be an obligate psychrophile? Explain! 

• bacteria that live below 60° F

• obligate = they have to live below 60°F or they die

• Facultative = prefer warmer temps but can tolerate these chillier conditions

• Listeria monocytogenes is a facultative psychrophile that can live in refrigerated and frozen foods and cause disease.

WHAT physiological differences do psychrophiles have to allow them survive in cold temperatures? 

• additional alpha helices in their secondary structure, which makes the proteins more flexible than usual.

• They also have more polar and fewer hydrophobic amino acids (which tend to fold in on themselves and be inflexible)

• their phospholipid bilayers have higher levels of unsaturated fatty acid tails to make them more fluid.

WHAT temperatures to hyperthermophiles live in? Do they have any adaptations that allow them to survive these extreme temps? Explain!

• These microbes live in conditions close to 200°F

• The archaea have a special adaptation that allows them to withstand the extreme heat: a phospholipid monolayer. The hydrophobic ends of the tails are covalently linked to keep the membrane from being ripped apart by the temperatures

WHAT are acidophiles? What pH range do they live in? What are some examples of environments where they live? 

• are microbes that grow best at low pH values – 5 or under.

• They require a high external concentration of hydrogen ions to maintain membrane stability.

• Bacteria that use sulfur compounds as electron donors fall into this category; quite a few soil fungi are also acidophiles.

• found in volcanic hot springs, geysers, acidic soils

WHAT are alkaliphiles? What pH range do they live in? What are some examples of environments where they live? 

• are microbes that grow best at high pH values – 8 or higher.

• These microbes (bacteria and fungi) can be found in alkaline soils or soda lakes.

WHY do alkaliphiles have a difficult time generating a proton motive force? How do they achieve this/get around this? 

• Because the external concentration of OH- ions is so high, generating a proton motive force can be a problem for some of these cells.

• Many use an Na+ ion force instead to generate ATP.

WHAT are neutrophiles? What pH range do they live in? What are some examples of environments where they live? 

• they grow between pH 6 -8.

• live in human body

WHAT category do most pathogens fall into regarding pH tolerance? Why?

The vast majority of human pathogens are neutrophiles, since most human environments fall within this pH range.

WHY is oxygen dangerous for some microbes? WHY are other bacteria able to live safely in oxygenated environments? 

• some bacteria lack enzymes to clear ROS causing their macromolecules to be oxidized.

• The bacteria that can safely live in oxygenated environments have the ability to clear/inactivate ROS.

WHAT are reactive oxygen species? WHY are they dangerous for cells? 

• toxic forms of oxygen that has electrons that are out of place

• dangerous bc they’ll try to steal electrons (oxidize) macromolecules to return their electron status to normal

• if the macromolecules get oxidized, the cell will die

WHAT types of enzymes can clear ROS? IS there a difference in the products of these reactions? Why does this matter? 

• Catalase: breaks down hydrogen peroxide (H2O2) into oxygen and water; can be tested in the lab by adding hydrogen peroxide to a culture of bacteria and looking for appearance of bubbles

• Peroxidase: breaks down H2O2 into water (no oxygen) but requires NADH

• Superoxide dismutase: combines two molecules of superoxide to form H2O2, which releases O2; usually paired with catalase in bacteria

• Superoxide reductase: reduces superoxide to form H2O2 without forming oxygen; typically found in obligate anaerobes

• there are differences in products most likely to benefit the microbe in its particular environment or the type of bacteria it is.

WHAT environment does an obligate aerobe have to live in? Do you think an obligate aerobe could cause infection in the GI tract? Why or why not? 

• must live in oxygen

• cannot infect GI tract bc no O2

• could infect skin or lungs bc high amount of O2

HOW does an obligate aerobe generate energy? What role does oxygen play? Explain! 

• They use oxygen as the final electron acceptor at the end of the ETC in aerobic respiration, which is the only way obligate aerobes can make ATP.

• exclusively use aerobic respiration

WHAT environment does an obligate anaerobe have to live in? WHY are these bacteria unable to tolerate oxygen? Do you think an obligate anaerobe could cause infection in the lungs? Why or why not? 

• no oxygen in environment

• they lack the ability to clear reactive oxygen species (ROS)

• Couldn’t cause infection in lungs bc high conc of O2 would kill them

• Could infect GI tract or in a deep wound surrounded by dead tissue.

HOW does an obligate anaerobe generate energy? 

They either use anaerobic respiration (where an alternative eacceptor is use at the end of the ETC) or they use anaerobic metabolism with a fermentation pathway.

WHAT environment is required by microaerophiles? WHY can they only tolerate small amounts of oxygen? WHERE do these bacteria cause disease in humans? 

• require a specific, small amount of oxygen in the environment.

• Yes, but they have limited enzymes to clear ROS (which is why they can only tolerate small amounts)

• They cause very localized infections in areas of the body with lower than atmospheric levels of oxygen – like the upper GI tract. Campylobacter is a foodborne illness that causes infection in the small intestine.

HOW do microaerophiles generate energy? 

Microaerophiles use aerobic respiration to make ATP (oxygen serves as the final electron acceptor at the end of the ETC).

WHAT environments can facultative aerobes live in? Do they have a preference? Why or why not? WHAT body locations can they cause infections in? 

• prefer oxygen in the environment but can survive without it.

• Facultative aerobes prefer to use oxygen for aerobic respiration because they can get lots more energy this way.

• Facultative anaerobes are incredibly versatile and can cause infections anywhere the body. These microbes can often become systemic (which means they have infected multiple body locations at the same point). E. coli and S. aureus are examples.

HOW do facultative aerobes generate energy? 

• if oxygen is present, they WILL use it.

• If there is no oxygen these microbes switch to either anaerobic respiration or anaerobic metabolism.

• If oxygen appears again, they will start using it for aerobic respiration

WHY do facultative aerobes grow better towards the top of an oxygen gradient tube? Explain! 

they prefer to use oxygen to make energy because it offers a higher yield of ATP

WHAT environments can aerotolerant anaerobes live in? Do they have a preference? Why or why not? WHAT body locations can they cause infections in? 

• can live in oxygen but don’t use it for metabolism.

• no preference, even in presence of O2 they don’t use it for metabolism, only use anaerobic respiration or anaerobic metabolism

• These microbes usually cause infections in anaerobic body locations (like the GI tract).

• The ability to tolerate oxygen means that spending time outside of a host or in transmission to a new host can easily occur.

• Enterococcus causes GI tract infections and is frequently a healthcare associated infection.

HOW do aerotolerant anaerobes generate energy? 

They will use either anaerobic respiration or anaerobic metabolism

WHY to aerotolerant anaerobes grow evenly through an oxygen gradient tube? WHY don’t they grow better towards the bottom of the tube?

• because they don’t have a preference over environment

WHAT environment do halophiles live in? Do all halophiles require high solute concentrations? WHY or why not? Explain! 

• elevated salt (NaCl) conditions

• no, some are obligate but some are facultative

• obligate halophiles that require these high salt concentrations and facultative halophiles (also called halotolerant) that prefer lower salt concentrations but can survive in higher salt concentrations.

HOW do halophiles keep from losing water to the environment? 

Halophiles increase their intracellular solute concentrations to match the solute concentration outside of the cell. 

1. The produce compatible solutes in the cytoplasm. In terms of osmolarity, all solutes are equal, so producing sugars and/or alcohols (substances that are safe to have in higher concentrations inside a cell) will safely raise the solute concentration.

2. They pump solutes into the cell. Microbes will import inorganic compounds into the cell to increase the solute concentration.

WHAT would happen to an obligate halophile placed in a low salt environment? Explain! 

• if an obligate halophile, it would die bc too much water would rush into the cell

• if facultative, it would adjust the intracellular solute concentration to match the environment

WHERE do halophiles cause infections in the body? 

Your skin and respiratory tract are pretty salt, so bacteria like S. aureus can cause infections there when other microbes cannot.

WHAT are extremophiles? Are they pathogens? What are some ways they adjust to their extreme environments?

• microbes that survive in extreme conditions.

• Some examples include extreme temperatures (very hot or very cold), extreme pH (very acidic or very basic) and extreme pressure (very high or very low external solute concentrations).

• Hyperthermophiles have phospholipid monolayers to keep their membranes intact, and extreme halophiles (that can live in up to 20% salt – like in pickle brine) use multiple ways to keep their intracellular solute concentrations high.

• no pathogens, nothing is extreme enough

WHEN do bacteria replicate DNA?

only occurs during binary fission, because that’s the only time bacteria need another copy of their chromosome

WHERE do bacteria replicate DNA? 

cytoplasm

WHAT are the important enzymes involved in DNA replication? (8)

• topoisomerase 1

• helicase

• ssbps

• primase - primer

• DNA pol 3

• DNA pol 1

• DNA ligase

• DNA gyrase

What does topoisomerase I do? 

• unwinds the supercoiled DNA

• requires ATP

What does helicase do? 

• unzips the DNA at the origin

• requires ATP