Microbiology Test 2

The current phylogeny of eukaryotes is based upon a) rRNA sequence comparisons. b) possession of photosynthetic pigments. c) mode of reproduction. d) locomotor structures.

A

The tail fibers on phages are associated with a) attachment. b) penetration. c) transcription of phage DNA. d) assembly of virus. e) lysis of host.

A

Which of the following genera preys on other bacteria? a) Bdellovibrio b) Caulobacter c) Hyphomicrobium d) Photobacterium e) Sphaerotilus

A

Describe how a dichotomous key is used when identifying bacteria.

A dichotomous key is essentially a flow chart of tests that give either a positive or negative result. Based on the results of a battery of tests, the organism can be identified.

If you discover a new type of nucleated cell in a lake near your home, how would you determine whether the cell is from a fungus, an alga, a protozoan, or a water mold?

A fungus would have a chitinous cell wall. An alga would contain chlorophyll. A protozoan would lack both a cell wall and chlorophyll. A water mold would contain cellulose in the cell wall (like the alga), but would not contain chlorophyll.

What is a mycosis? Give an example.

A mycosis is a disease caused by growth of a fungus. Examples are athlete's foot (tinea), candidiasis, histoplasmosis, coccidioidomycosis, cryptococcal meninoencephalitis, and histoplasmosis.

What is the difference between acute and persistent infections?

Acute infections are of sudden onset and short duration; persistent infections can continue with/out signs and symptoms for years or even a lifetime.

Compare and contrast the relationships of Agrobacterium and Rhizobium species with plants.

Agrobacterium and Rhizobium both derive nutrients from plants. However, Agrobacterium does this by harming the plant (causing a tumor) whereas Rhizobium provides a benefit to the plant (nitrogen fixation).

What characteristics do all algae have in common?

All algae are photosynthetic, but lack the vascular systems of plants, and have relatively simple reproductive structures.

Capsids are composed of a) DNA. b) RNA. c) protein. d) lipids. e) polysaccharides.

C

Classification of viruses is based on all of the following except a) type of nucleic acid. b) shape of virus. c) size of virus. d) host infected. e) strandedness of nucleic acid.

C

Explain how an insect might act as a mechanical vector for one disease and a biological vector for another. Members of this group have chitinous cell walls. a) Algae b) Protozoa c) Fungi d) Helminths

C

Filamentous phages a) infect animal and bacterial cells. b) cause their host cells to grow more quickly. c) are extruded from the host cell. d) undergo assembly in the cytoplasm. e) degrade the host cells' DNA.

C

If the GC content of two organisms is 70%, the a) organisms are definitely related. b) organisms are definitely not related. c) AT content is 30%. d) organisms likely have extensive DNA homology. e) organisms likely have many characteristics in common.

C

Which of the following archaea would most likely be found coex¬isting with bacteria? a) Nanoarchaeum b) Halobacterium c) Methanococcus d) Picrophilus e) Sulfolobus

C

Which of the following is mismatched? a) Trematode—fluke b) Mosquito—malaria c) Baker's yeast—algae d) Apicomplexan—protozoa

C

Which of the following statements regarding protists is false? a) They include both autotrophic and heterotrophic organisms. b) They include both microscopic and macroscopic organisms. c) They are an intermediate host in schistosomiasis. d) They include algae and protozoa.

C

How do oncogenes differ from protooncogenes?

Oncogenes are in the virus; proto-oncogenes are in the animal host. The nucleotide sequences of both are very similar.

Members of this group are photosynthetic. a) Algae b) Protozoa c) Fungi d) Helminths

A

Quantitating viral titers of both phage and animal viruses fre¬quently involves a) plaque formation. b) quantal assays. c) hemagglutination. d) determining the ID50. e) counting of virions by microscopy.

A

All algae have a) chlorophyll a. b) cell walls that contain agar. c) holdfasts. d) red tides.

A

Name and describe the areas of taxonomy. Explain the basis of the three-domain systems of classification.

16S RNA nucleotide sequence analysis showed that all organisms could be separated into three major groups - Bacteria, Archaea, and Eukarya

Acute infections of animals 1. are a result of productive infection. 2. generally lead to long lasting immunity. 3. result from integration of viral nucleic acid into the host. 4. are usually followed by chronic infections. 5. often lead to tumor formation. a) 1, 2 b) 2, 3 c) 3, 4 d) 4, 5 e) 1, 5

A

What kind of bacteria might compose the subsurface scum of pol¬luted ponds?

Anoxygenic phototrophs

All of the following genera are spirochetes except a) Borrelia. b) Caulobacter. c) Leptospira. d) Spirochaeta. e) Treponema.

B

If an acid fast bacterium is detected in a clinical sample, then the organism could be a) Cryptococcus neoformans. b) Mycobacterium tuberculosis. c) Neisseria gonorrhoeae. d) Streptococcus pneumoniae. e) Streptococcus pyogenes.

B

Temperate phages can do all of the following except a) lyse their host cells. b) change properties of their hosts. c) integrate their DNA into the host DNA. d) bud from their host cells. e) become prophages.

B

The "O157:H7" of E. coli O157:H7 refers to the a) biotype. b) serotype. c) phage type. d) ribotype. e) antibiogram.

B

The dormant forms of which of the following genera are the most resistant to environmental extremes? 1. Azotobacter 2. Bacillus 3. Clostridium 4. Myxobacteria 5. Streptomyces a) 1, 2 b) 2, 3 c) 3, 4 d) 4, 5 e) 1, 5

B

The sequence of which ribosomal genes are most commonly used for establishing phylogenetic relatedness? a) 5S b) 16S c) 23S d) All of these are commonly used.

B

Which of the following genera are known to fix nitrogen? 1. Anabaena 2. Azotobacter 3. Deinococcus 4. Mycoplasma 5. Rhizobium a) 1, 3, 4 b) 1, 2, 5 c) 2, 3, 5 d) 2, 4, 5 e) 3, 4, 5

B

Which of the following is best for determining the evolutionary relatedness? a) Ability to form endospores b) 16S ribosomal RNA sequence c) Sugar degradation d) Motility

B

Which of the following is mismatched? a) Plasmodium—malaria b) Trypanosomes—dysentery c) Dinoflagellates—paralytic shellfish poisoning d) Nematode—trichinellosis

B

Which of the following statements regarding protozoa is false? a) Some protozoa lack mitochondria. b) Some protozoa contain chlorophyll. c) Some protozoa are parasitic. d) Malaria is caused by a protozoan.

B

Which of the following statements regarding tapeworms is false? a) They absorb nutrients from the host through their body wall. b) They complete their life cycles in a single host. c) They are hermaphroditic. d) They cannot be transmitted from human to human.

B

Why are RNA viruses and retroviruses more error-prone in their replication than DNA viruses?

Because the enzymes that are involved in replication of the RNA have no proof-reading ability.

Name two genera of endospore forming bacteria. How do they differ?

Clostridium, which are obligate anaerobes, and Bacillus, which are either aerobes or facultative anaerobes.

All of the following genera are obligate intracellular parasites except a) Chlamydia. b) Coxiella. c) Ehrlichia. d) Mycoplasma. e) Rickettsia.

D

If two microbial isolates have similar but different 16S rRNA sequences they are probably a) both motile. b) both pathogens. c) both cocci. d) members of the same domain. e) the same strain.

D

If you read that coliforms had been found in a lake, the report could have been referring to which of the following genera? a) Bacteroides b) Bifidobacterium c) Clostridium d) Escherichia e) Streptococcus

D

Influenza vaccines must be changed yearly because the amino acid sequence of the viral proteins change gradually over time. Based on this information, which is the most logical conclusion? The influenza virus a) is enveloped. b) is non enveloped. c) has a DNA genome. d) has an RNA genome. e) causes a persistent infection.

D

Prions a) contain only nucleic acid without a protein coat. b) replicate like HIV. c) integrate their nucleic acid into the host genome. d) cause diseases of humans. e) cause diseases of plants.

D

Thermoplasma and Picrophilus grow best in which of the follow¬ing extreme conditions? a) Low pH b) High salt c) High temperature d) Low pH and high temperature e) High salt and high temperature

D

When hydrogen peroxide is placed on a colony of an unknown bacterium, bubbles form. Based on this information, you can conclude that the bacterium a) is Staphylococcus epidermidis. b) is a lactic acid bacterium. c) is beta hemolytic. d) is catalase positive. e) can cause strep throat.

D

Which of the following statements about fungi is false? a) Fungi may cause disease when growing in or on the human body. b) Some fungi produce toxins that can kill humans. c) Fungal spores may cause allergic responses in humans. d) Systemic mycoses are common in otherwise healthy adults.

D

Paper recycling companies refuse to collect paper products that are contaminated with food or have been sitting wet for a day. A col¬lege sorority member who is running a recycling program on campus wishes to know the reason for this. What reason did the chemist who works for the recycling company probably give her for this policy?

Decaying food and wet paper are very likely to be contaminated with fungi. Many of the fungi found on food and wet paper produce enzymes capable of breaking down cellulose and other strengthening components of paper. Recycled paper is not treated in any way that kills the fungal spores. Any treatments used to destroy fungal spores would be expensive or potentially dangerous for users of the recycled paper products. Any spores that make their way into recycled paper products would ultimately germinate and decay the product or could contaminate anything packaged in the product.

Why are nonenveloped viruses generally more resistant to disinfectants than are enveloped viruses?

Disinfectants damage the lipid bilayer of the envelope

A catalase negative colony growing on a plate that was incubated aerobically could be which of these genera? a) Bacillus b) Escherichia c) Micrococcus d) Staphylococcus e) Streptococcus

E

All phages must have the ability to 1. have their nucleic acid enter the host cell. 2. kill the host cell. 3. multiply in the absence of living bacteria. 4. lyse the host cell. 5. have their nucleic acid replicate in the host cell. a) 1, 2 b) 2, 3 c) 3, 4 d) 4, 5 e) 1, 5

E

If you examined the acidic runoff from a coal mine, which of the following genera would you most likely find growing there? a) Clostridium b) Escherichia c) Lactic acid bacteria d) Thermus e) Acidithiobacillus

E

The "breath test" for Helicobacter pylori infection detects the presence of which of the following? a) Antigens b) Catalase c) Hemolysis d) Lactose fermentation e) Urease

E

Which of the following is false? a) Tropheryma whipplei could be identified before it had been grown in culture. b) The GC content of DNA can be measured by determining the temperature at which double stranded DNA melts. c) Sequence differences between organisms can be used to assess their relatedness. d) Based on DNA homology studies, members of the genus Shigella should be in the same species as Escherichia coli. e) Gel electrophoresis is used to determine the serotype of an organism.

E

Which of the following is the newest taxonomic unit? a) Strain b) Family c) Order d) Species e) Domain

E

What unique motility structure characterizes the spirochetes?

Endoflagella

Soil often goes through periods of extreme dryness and extreme wetness. What characteristics of Clostridium species make them well suited for these conditions?

Endospores of Clostridium survive the dry periods in the soil. When soil becomes saturated with water, however, conditions often turn anaerobic because the diffusion of gases is limited. Under these anaerobic conditions, Clostridium endospores can germinate and thrive, without competition from obligate aerobes.

What are the major differences between a prokaryotic cell and a eukaryotic cell?

Eukaryotes have a true nucleus surrounded by a double membrane as well as other membrane-bound organelles. They may contain mitochondria and chloroplasts. Prokaryotes do not have a membrane-bound nucleus and do not contain other membrane-bound organelles.

What kind of bacterium might be responsible for plugging the pipes in a sewage treatment facility?

Filamentous sulfur oxidizers such as Thiothrix and Beggiatoa.

Fungi are known for growing and reproducing in a wide range of environmental extremes in temperature, pH, and osmotic pres¬sure. What does this tolerance for extremes indicate about fungal enzymes?

Fungal enzymes must be highly resistant to denaturation at extremes of pH, temperature, and salt concentrations that would denature enzymes of other organisms. If this were not the case, fungal enzymes would be denatured under such conditions, as are almost all other enzymes, and the organism could not survive.

A researcher interested in investigating the genetic relationship of mitochondria to bacteria must decide on the best method to study this. What advice would you give the researcher?

Mitochondria most likely lost many of their ancestral biochemical characteristics because of their long relationship of inhabiting the eukaryotic cell. An analysis of its genome would probably provide most information. Its genome can then be compared to the genomes of other bacteria to see which it correlates with the most.

Name a disease for which humans are an intermediate host and another for which humans are a definitive host. Give an example of a disease in which humans are a dead end host

Humans are an intermediate host in malaria, African sleeping sickness, and plague. Humans are a definitive host in schistosomiasis and some tapeworm diseases. Humans are a dead-end host in "swimmer's itch."

Give three examples of energy sources used by chemolithotrophs.

Hydrogen gas (H2), hydrogen sulfide (H2S), and ammonia (NH3).

Name and describe the areas of taxonomy.

Identification — the process of characterizing organisms. Classification — the process of arranging organisms into similar or related groups. Nomenclature — the assignment of names.

How is specialized transduction different from generalized transduction?

In specialized transduction, only genes near the site on the bacterial chromosome where the phage has integrated can be transduced. In generalized transduction, any gene of the bacterial genome can be transduced.

Why is it virtually impossible to eradicate (eliminate) a disease caused by a zoonotic virus?

It would be impossible to eradicate all of the animal hosts.

Compare and contrast the organisms that cause malaria and African sleeping sickness and their transmission.

Malaria is caused by protozoan apicomplexan species of Plasmodium spread by Anopheles mosquitoes. The organism replicates in red blood cells of the host and are released in waves that result in cyclic presentation of symptoms. African sleeping sickness is caused by protozoan kinetoplastid species of Trypanosoma spread by tsetse flies of the genus Glossina. They also produce waves of symptoms as the organisms switch antigen surface proteins.

Microbiologists debate the use of biochemical similarities and cell features as a way of determining the taxonomic relationships among prokaryotes. Explain why some microbiologists believe these similarities and differences are a powerful taxonomic indica¬tor, whereas others think they are not very useful for that purpose.

Microbiologists in favor of using biochemical differences and cell features for taxonomy are supported by the knowledge that organisms expressing similar growth characteristics often share genetic similarities and origins. Those opposing this view site evidence that unrelated microorganisms living in similar environments may take on similar characteristics by natural selection.

Why is MALDI-TOF MS particularly important in clinical microbiology?

Microorganisms in a colony can often be identified in less than15 minutes, which is considerably faster than

Why are few lichens found in industrial areas?

Polluted air associated with industry may contain toxic metals, sulfur dioxide, or ozone. Lichens absorb these, but are unable to excrete them. Thus they are lethal to the lichen.

How is the life cycle of Epulopiscium species unusual?

Rather than undergoing binary fission, they enlarge considerably, finally lysing to release up to seven daughter cells.

Describe the life cycle of Schistosoma mansoni.

Sexual reproduction takes place in humans where the organisms cause schistosomiasis. Larvae released into water can infect an intermediate host, a type of snail. A swimming form is released from the snail and attaches to a human where it completes the life cycle.

In what ways are fungi economically important?

Some fungi, such as mushrooms, are eaten, while others are used in the production of foods such as beer, wine, and bread. Fungi produce many of the common antibiotics. Some fungi are used as tools for genetic studies. Fungi have been genetically engineered to produce important hormones such as insulin and somatostatin, the human growth hormone. Since there are fungi that can grow on almost any organic material, fungi destroy large amounts of food products and other materials. Fungi also cause some major diseases of plants, especially food crop plants.

In what way does the metabolism of Streptococcus species differ from that of Staphylococcus species?

Streptococcus species are obligate fermenters; they cannot respire even when growing in the presence of O2. Staphylococcus species are facultative anaerobes; they respire when O2 is available but ferment when it is not.

Why must (-) strand but not (+) strand RNA viruses bring their own replicase into a cell?

The (-) stand can not be translated into any required virus proteins whereas the (+) strand can act as mRNA

Describe how prions propagate.

The abnormal prion protein binds to the normal cellular normal prion protein and converts it to the abnormal form.

A molecular biologist working for a government run fishery in Vietnam is interested in controlling the dinoflagellate Pfisteria in fish farms. Pfisteria produces toxins that stun the fish and then causes the skin to slough off, allowing the parasites to dine on the tissues of the fish. He needs to develop a treatment that kills Pfisteria without harming the fish or the beneficial green algae that serve as food for the young fish. What strategy should the biologist consider for developing a selective treatment?

The compound must be specific enough to kill the dinoflagellate without killing other algae. So, one approach is to first try treatments that affect the chloroplast. Treatments altering the function of chloroplasts would not harm the fish and protists. Next, the treatment must select the specific photosynthetic pigments used by Pfisteria. Many of the beneficial algae have chloroplasts that differ from those of Pfisteria and will not be affected by the treatments.

How is the replication cycle of lambda phage different from that of T4?

The genome of lambda phage can integrate in the bacterial genome and replicate in concert with the bacterial DNA. T4 cannot do this but undergoes a replication cycle that results in cell lysis.

A friend who has lakefront property and cherishes her lush green lawn complains of the green foul smelling scum on the lake each summer. Explain how her lawn might be contributing to the problem.

The green scum is probably due to overgrowth of cyanobacteria. The fertilizer she applies to her lawn, which is probably high in nitrogen and phosphate, might be leaching into the lake and enhancing the growth of the photosynthetic bacteria.

What is lysogenic conversion?

The modification of certain properties of a bacterial cell as a result of carrying a temperate phage in its genome. The new properties are encoded in the phage DNA.

A public health physician isolated large numbers of phages from rivers used as a source of drinking water in western Africa. The physician is very concerned about humans becoming ill from drinking this water, although she knows that phages specifically attack bacteria. Why is she concerned?

The phages likely were released from bacteria, some of which might be pathogens, this suggests that dangerous bacteria might be in the environment.

When DNA probes are used to detect specific sequence similarities in bacterial DNA, the probe is heated and the two strands of DNA are separated. Why must the probe DNA be heated?

The probe must bind to the target DNA molecule by base pairing. If the probe is in the double-stranded form, this base pairing cannot occur. Both the target DNA and the probe must be single-stranded for the base pairs to recognize each other.

What is the role of a prophage in persistent infections?

The prophage can be activated and once again cause disease

Some organisms use sulfur as an electron donor (a source of energy), whereas others use sulfur as an electron acceptor. How can this be if there must be a difference between the electron affinity of electron donors and acceptors for an organism to obtain energy?

The same organism could not use sulfur as both an electron acceptor and donor. Any species that uses sulfur as a donor will use a chemical such as molecular oxygen that has a much greater affinity for electrons as an acceptor. Any species that uses sulfur as an acceptor will use a chemical such as H2 (which has a much lower affinity for electrons) as an energy source.

Researchers debate the evolutionary value to the virus of its abil¬ity to cause disease. Many argue that viruses accidentally cause disease and only in animals that are not the natural host. They state that this strategy may eventually prove fatal to the virus's future in that host. It is reasoned that the animals will eventually develop immune mechanisms to combat the virus and prevent its spread. Another group of researchers supports the view that disease is a way to enhance the survival of the virus. What position would you take, and what arguments would you give to support your view?

The second view seems more probable. The only virus disease that has been eliminated has been small pox and only after extensive and wide-spread immunization of all susceptible human populations. On the other hand, even with extensive immunization, there will always be susceptible populations to a virus disease so that the viruses can spread and continue to survive in the population.

How have species of Streptomyces contributed to the treatment of infectious diseases?

They are the natural source of many medically important antibiotics.

What characteristics of Azotobacter species protect their nitroge¬nase enzyme from inactivation by O2?

They have a high respiratory rate and thus consume O2 so rapidly that an anaerobic environment is produced inside the cell. In addition, a protein in the cell binds nitrogenase, thereby protecting it from O2 damage.

A filter capable of preventing bacteria from passing is placed at the bottom of a U tube to separate the two sides. Streptomycin resistant cells of a bacterial strain are placed on one side of the filter and streptomycin-sensitive cells are placed on the other side. After incubation, the side of the tube that originally contained only streptomycin-sensitive cells now contains some streptomycin-resistant cells. Give three possible reasons for this observation. What further experiments would you do to determine the correct explanation?

Three possible reasons: 1. The streptomycin sensitive cells mutated to resistance. 2. The streptomycin sensitive cells were transformed to streptomycin resistance by DNA- mediated transformation 3. The streptomycin sensitive cells were transduced to streptomycin resistance by transduction To distinguish between these possibilities, the number of streptomycin resistant cells arising from streptomycin sensitive should be compared under the following conditions: 1. How many resistant cells arise when the sensitive cells are plated on streptomycin containing medium in the absence of resistant cells. The possibility of reversion 2. Is the number of resistant cells reduced if DN'ase is added to both sides of the filter, 3. Irradiate the resistant cell population and look for clearing of the culture to indicate lysis and suggest phage induction.

In figure 10.15, how would the curve appear if the GC content of the DNA sample were increased? How would the curve appear if the AT content were increased?

When the GC content increases, the melting point will increase due to the greater number of hydrogen bonds between G and C compared to the number between A and T. The whole curve will shift to the right, to higher temperatures. When the AT content increases, the melting point decreases and the whole curve would shift to the left.

A student argues that it makes no sense to be concerned about coli¬forms in drinking water because they are harmless members of our normal microbiota. Explain why regulatory agencies are concerned about coliforms.

While it is true that coliforms generally do not cause disease (with the exception of certain strains of E. coli), their presence in drinking water indicates that the water is likely contaminated with fecal pollution. Intestinal pathogens, such as Salmonella, Shigella, and many viruses are passed in feces and therefore might be present in the water. Rather than trying to detect each and every intestinal pathogen, regulatory agencies look for organisms that are commonly found in feces and are easy to detect.

What are the differences among a yeast, a mold, and a mushroom?

Yeasts are single-celled fungi that reproduce by binary fission or budding. Molds are filamentous fungi composed of a collection of hyphae known as a mycelium. Mushrooms are the macroscopic reproductive structures of some members of the Basidiomycetes.