Micro test 3

Which fluorescent molecule enables visualization of living microorganisms?

GFP

Wolbachia pipientis is a type of Alphaproteobacteria that multiples in the vacuoles of host cells. What are these?

Vacuoles are organelles that provide large storage compartments in eukaryotic cells.

The biggest limitation of traditional light microscopy and electron microscopy methods is that they are unable to reveal

genetic and functional diversity of microorganisms in the habitat under study.

The science of microbial ecology deals with

how the activity and biodiversity of microbial communities affect microbial interactions with each other and the environment.

A method of genetic fingerprinting that relies on the location of small subunit rRNA genes on DNA fragments is called __________.

ribotyping

A NASA ecologist wants to design an instrument to send to Mars on the next space probe to determine whether living organisms ever carried out carbon fixation on that planet. Suggest an assay that she could use on Martian soil samples.

13C/12C stable isotope analysis

What is an advantage of a monolayer cell membrane, as is found in some Archaea?

A monolayer membrane is more stable at high temperatures.

Which of the following populations would be most likely to demonstrate genetic drift?

A researcher transfers bacteria into fresh medium but accidentally collects only a very small quantity of bacteria in the process.

Why would it be highly advantageous to a cell to form a mutualism with a prokaryote capable of aerobic cellular respiration?

Aerobic cellular respiration involves an electron transport chain with oxygen as the terminal electron acceptor. This produces large amounts of ATP as the electron transport chain produces the greatest amount of ATP in cellular respiration.

Alphaproteobacteria can be distinguished by which of the following characteristics?

All the organisms are gram-negative.

Actinobacteria are called high GC Gram positive bacteria. What does this tell you about them?

Because guanine bonds to cytosine with 3 hydrogen bonds, compared with only 2 hydrogen bonds for adenine-thymine pairs, the DNA will have a relatively high melting point compared with low GC bacteria.

Compare and contrast the survival strategies of extreme halophiles and extreme thermophiles.

Both of these groups of microorganisms thrive under what humans would consider to be very harsh environments--very high salt concentrations in the case of the halophiles and high temperatures for the thermophiles. Interestingly, they use some of the same strategies to survive under these very dissimilar situations. Both groups accumulate potassium or other counterions in their cells. This helps to balance the osmotic pressure for the halophiles, whereas in the thermophiles these ions serve to stabilize DNA and proteins and help prevent them from denaturing.

Which statements describe the evidence that supports the endosymbiotic theory?

Chloroplasts and mitochondria have a double-stranded, circular piece of DNA in their cytoplasm.

RNA polymerases play an important role in which of the following processes?

DNA replication

Early microscopic studies of the human intestinal microbiota revealed the presence of many prokaryotic cells. However, these were erroneously thought to be dead (non-viable) cells. Explain how this misconception may have arisen. What techniques are used today to avoid missing microbial populations in ecological samples?

Early microbiological studies were based upon cultivation of the microbes present. Although many cells were visible microscopically, only a very small proportion grew under laboratory conditions. This was primarily due to the abundance of anaerobes in the intestinal lumen. The initial culture conditions were primarily aerobic and therefore precluded the cultivation of the more numerous anaerobes. This culture bias led some to conclude that Escherichia coli was one of the most numerous microbes in the colon. In fact, E. coli accounts for only about 0.5% of the microbes present. Today, DNA based techniques such as metagenomic analysis can be used to identify microorganisms based solely upon their genetic content. Culture bias is less of a problem with such techniques.

Halobacteria tend to have fewer hydrophobic amino acids in their proteins than other bacteria. Why?

In a highly saline environment, hydrophobic proteins have an increased likelihood of precipitating out of solution.

Which of the following is NOT evidence that mitochondria originated as independent prokaryotes, as stated by the endosymbiont hypothesis?

Mitochondria have a membrane that includes peptidoglycan.

Although oxygen is essential for many organisms (obligate aerobes), other organisms do not need it (microaerophiles, facultative anaerobes) or may be harmed by it (obligate anaerobes). Why is oxygen harmful to some organisms?

Oxygen can form reactive oxygen species that can be damaging to organisms without protective mechanisms.

Which of the following best explains the endosymbiont hypothesis?

Prokaryotes capable of cellular respiration and prokaryotes capable of photosynthesis took up residence in larger prokaryotes, forming obligate mutualisms. The prokaryotes capable of cellular respiration evolved into mitochondria and the prokaryotes capable of photosynthesis evolved into chloroplasts.

Scientists believe life may have begun as an RNA world because __________.

RNA can bind small molecules RNA can have catalytic activity RNA is essential to processes found in all cells

What is one piece of evidence that supports the RNA world hypothesis?

RNAs can have catalytic activity. (RNAs can have catalytic activity (e.g., ribozymes) and are important cofactors and components of many molecules in living cells.)

What are some common mechanisms by which bacteria are able to survive antibiotic exposure?

Resistant bacteria may modify the antibiotic or pump the antibiotic out of the cell.

Compare and contrast the Crenarchaeota with the Euryarchaeota.

The Crenarchaeota and Euryarchaeota are the two largest clades within the Archaea today. They each contain a diverse collection of prokaryotes. The Crenarchaeota have the widest range of temperature optima on the planet. Many of the initial isolates found thrive in environments above the boiling point of water. More recently, abundant examples of mesophilic (room temperature) and even psychrophilic (thriving at or below the freezing point of pure water) have been found in marine environments. The Euryarchaeota are more diverse in terms of their metabolism. This group includes the phototrophic Archaea, extreme halogens, and the methanogens. These unique processes are not found elsewhere on the planet.

Some organisms seem to change names, for example Vibrio fischerii is now Aliivibrio fischerii. How can it be known which is the proper name?

The official source is the International Journal of Systematic and Evolutionary Microbiology.

Which of the following would be most likely in an organism that thrives at a very high temperature, as opposed to in an organism that thrives at low temperatures?

a cell membrane with a high proportion of saturated fatty acids

There is a small lake on campus that students like to use for recreational activities. A study has begun on the microbial community in the lake at different times of the year. In order to quickly determine the approximate number of reproducing bacteria in a sample, it would best to use __________.

a fluorescent viability stain

Phylogenetic trees for bacteria are constructed by which of the following?

analyzing molecular similarities and then using computer algorithms or optimality criteria to construct phylogenetic trees showing hypothesized evolutionary relationships

For organisms to be considered members of the same species, they must __________.

be genetically and phenotypically cohesive

According to the RNA world hypothesis, which of the following was the correct sequence of developments?

biological building blocks (e.g., amino acids, sugars, and nucleosides), then RNA (including catalytic and self-replicating RNA), then protein synthesis, then DNA, then lipid bilayers surrounding early cellular life

What has occurred when organisms share a trait that was NOT inherited from a common ancestor?

convergent evolution

Which of the following techniques can link prokaryotic phylogeny and function?

environmental genomics and stable isotope probing

A change in allele frequencies in a set of organisms over time is called __________.

evolution

Proteobacteria have many metabolic similarities even though the group is so phylogenetically diverse. What process most likely contributed to these similarities?

exchanges of genetic material between mature, adult organisms

What technique(s) can be used to characterize the phylogenetic composition of a microbial community without culturing any of the members?

fluorescent in situ hybridization

For microbial biodiversity studies, it is common to identify the ________ rather than the ________ as a measure of biodiversity.

genes / organisms themselves

The phylogenetic analysis of complex microbial communities often targets small subunit (SSU) ribosomal RNA genes. This is because rRNA is found in all organisms and __________.

is highly conserved over evolutionary time

Which technique would be used to estimate the concentration of naturally occurring Escherichia coli in a wastewater sample?

most probable number (MPN) method

The best choice for estimating the viable cell number of a water sample would be the __________.

most probable number method

You would like to test the hypothesis that ammonia-oxidizing Archaea are more active and abundant than ammonia-oxidizing Bacteria in coastal marine water. What technique(s) or experiment(s) could you use to test this hypothesis?

stable isotope probing using 15N labeled ammonia

What was the LUCA?

the last organism prior to the divergence of bacteria and archaea

The genes for 16S rRNA are used to determine genetic relatedness because __________.

these genes are of adequate length to show deep relationships

Which of the following correctly matches a form of horizontal gene transfer with its description?

transduction - the transfer of genetic material involving a phage

Enteric pathogens such as Salmonella can be distinguished from non-pathogens such as Serratia by __________.

type of fermentation