Microbiology Old exam questions exam 2

commonly found in low pH mines.

Acidophilic aerobic iron oxidizers

Many pharmaceutical drugs specifically inhibit transcription in Bacteria but not Archaea or Eukarya. Why would drugs that inhibit transcription only affect Bacteria and not Archaea even though they are both prokaryotes?

Archaea and Eukarya have very similar RNA polymerases that are different than bacterial RNA polymerases.

The fate of carbon fixed by primary producers such as phytoplankton occurs by all EXCEPT: A) Consumption by zooplankton grazers B) Consumption by other phytoplankton C) Consumption by heterotrophic bacteria D) Processed by viruses

B) consumption by other phytoplankton

The fate of phytoplankton-derived carbon includes all the following EXCEPT

Consumption by other phytoplankton grazers

What happens when excess fertilizer runoff gets deposited into rivers?

Cyanobacterial growth increases (algal bloom status), which supports higher bacterial

What is the difference between a facultative anaerobe, an aerotolerant anaerobe, and an obligate anaerobe?

Facultative anaerobes can use oxygen to produce more ATP than without it. Aerotolerant anaerobes are unaffected by oxygen. Obligate anaerobes require an oxygen-free environment to survive.

Diazotrophs maximize nitrogenase activity by

producing specialized structures or fixing N2 at times when oxygen is absent to protect nitrogenase from oxygen

According to bacterial abundance studies done so far on soils, the ________ represent the most abundant phylum.

proteobacteria

The Fe and Mn cycles include

reduced and oxidized forms that are very chemically reactive.

One important difference between the C, N, and S cycles and the P, Ca, and Si cycles is that

the P, Ca, and Si cycles do NOT involve redox changes or gaseous forms that can alter earth atmospheric chemistry

Lichens are a mutualistic association of a fungus and either an alga or a cyanobacterium in which

the fungus protects the photosynthetic partner from erosion.

Microorganisms were probably restricted to the oceans and subsurface environments until

the ozone layer was made.

In mycorrhizal mutualisms between plants roots and fungi

the plant supplies carbohydrates to the fungus and the fungus supplies phosphorus and nitrogen to the plant.

In mycorrhizal mutualisms between plants roots and fungi,

the plant supplies carbohydrates to the fungus and the fungus supplies phosphorus and nitrogen to the plant.

Under what scenario would an oligotroph outcompete a copiotroph in the soil?

Under low nutrient conditions

A computer program recognizes an ORF by looking for ribosomal binding sites, start codons, and stop codons with an appropriate number of nucleotides between each element. What is a drawback of this approach?

Unusual, but legitimate genes and non-coding RNA may be missed.

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

is highly conserved over evolutionary time

An operon is a useful genetic element, because it

allows coordinated expression of multiple related genes in prokaryotes.

What metabolism would be favored when there is a lack of electron acceptors?

anaerobic fermentation

Phototrophs

are characterized by using inorganic carbon for growth.

Nitrifying Thaumarchaeota outcompete nitrifying bacteria in many aquatic and terrestrial environments because Thaumarchaeota

are well-adapted to very low nutrient and electron donor concentrations.

Chloroplasts and mitochondria originated from ________ by a process known as ________.

bacteria / endosymbiosis

All of the following are true of biofilms EXCEPT that __________

biofilms are composed of only one species at a time

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 metabolic diversity of photosynthetic bacteria stems from different

light-harvesting complexes, electron donors, and organic compounds they produce.

Prosthecae are an adaptation for

low nutrient aquatic environments.

Both deletions and insertions occur during the evolution of microbial genomes. Insertions bring in new genes that may be useful for the cell, but deletions

may increase fitness of a microorganism by eliminating unneeded genes.

In Bacteria, the MOST common oxidized form of nitrogen is ________ and of sulfur is ________.

nitrate / sulfate

Which part of the nitrogen cycle increases the chances for nitrogen to get leached from soils into aquatic ecosystems?

nitrification (ammonium to nitrate)

Which phylum harbors the MOST functional diversity observed and also has the MOST cultured representatives?

Proteobacteria

Which bacterial trait enhances colonization of phytoplankton species

Quorum sensing molecules

The first catalytic and self-replication biological molecule was most likely

RNA

Chemical reactions involving ________ have been proposed as energy-yielding reactions for primitive organisms.

S, and H2

Thermostable proteins tend to have additional features that improve thermostability. Which of the following is NOT one of these features? A) increased ionic interactions on the protein surfaces B) highly hydrophilic cores C) decreased tendency of the protein to unfold D) highly hydrophobic cores

(B) highly hydrophilic cores

Which species does NOT produce endospores? A) Bacillus cereus B) Clostridium pasteurianum C) Listeria monocytogenes D) Paenibacillus popilliae

(C) listeria monocytogenes

Which of the following is NOT a member of the Eukarya? A) protists B) fungi C) viruses D) red algae

(C) viruses

What is a reason that functional traits are seen in different species?

(all) (A) Gene loss (B) Convergent evolution (C) Horizontal gene flow

How can DNA binding proteins regulate transcription?

(all) A) DNA binding proteins can catalyze transcription. B) DNA binding proteins can block transcription. C) DNA binding proteins can activate transcription.

Copiotrophs

- are characterized by having high growth rates in environments with readily available resources. - are characterized being negatively impacted by environmental stressors such as drying-rewetting.

Oligotrophs

- are characterized by having low rRNA operon copy number - are characterized as having growth advantages in nutrient limited environmental conditions

mechanisms contributing to the maintenance of genetic variation in mutualisms

1) *Stabilizing mechanism*: - high partner quality might be favored by natural selection (but does not explain variation) - selective process that can increase the likelihood that high-quality mutualists remain in the population 2) *Discrimination mechanism* - partner choice (sanctions, one-to-many partner fidelity feedback, screening)

Which of the following statements is FALSE? A) A higher turnover of genes leads to increased genotypic diversity within a population. B) Genotypic diversity is maintained through species interactions and gene flow. C) Environmental heterogeneity maintains low genotypic diversity within a population. D) Stable environmental conditions select for decreased genotypic diversity within a population.

C) Environmental heterogeneity maintains low genotypic diversity within a population

All of the following are true of biofilms EXCEPT that A) biofilms protect organisms from antibiotics B) biofilms form on submerged surfaces in nature C) biofilms are composed of a single microbial species D) biofilm formation and dispersal are regulated processes

C) biofilms are composed of a single microbial species

Which of the following bioenergetic processes CANNOT occur in hyperthermophiles? A) chemoorganotrophy B) chemolithotrophy C) photosynthesis D) chemoorganotrophy, chemolithotrophy, and photosynthesis

C) photosynthesis

What is a reason why hospital acquired infections are common in hospitals today?

Decreased competition between pathogenic and environmental/non-pathogen microbes contributes to persistence of pathogens inside hospitals.

Which statement is TRUE about plant-microbe mutualisms?

Endomycorrhizal fungi enhance phosphorus acquisition for host plant, while fungi receive carbon.

Why is it challenging to study phylogenetic relationships in microorganisms?

Environmental selection can result in similar metabolic adaptations in unrelated microbial species

commonly found in deep sea vents.

H2-oxidizing hyperthermophiles

The microorganisms that are thought to resemble the first cellular forms of life on Earth are

H2-oxidizing hyperthermophiles.

What will most likely result from elevated CO2 effect in legume-dominated plant communities?

Heterotrophic bacterial activity will increase.

What molecular feature provides thermal stability on ribosomes and assists in protein synthesis for microbes living in high temperatures?

High GC content of the ribosomal RNAs

What mechanism supports the maintenance of genetic variation in mutualisms?

High partner quality

Which group in Bacteria lacks cell walls?

Mycoplasma

If an excess amount of nitrogen fertilizer was applied to a soybean field,

N2 fixation rate would decrease

commonly found in iron-rich surface waters.

Neutrophilic aerobic iron oxidizers

Near-shore marine waters typically contain higher microbial numbers than the open ocean. Why?

Oxygen minimum zones (OMZ) - Regions of oxygen-depleted waters at intermediate depths - High oxygen demand - Nutrient rich areas - High levels of denitrificaDon and anammox - OMZs are expanding

How are plasmids different than chromosomes?

Plasmids contain genes that are NOT essential for cellular growth and replication.

How do arbuscular mycorrhizae (AM) help plants obtain more nutrients from the soil?

The AM increase the total surface area to absorb more nutrients.

Which organism would likely harbor the MOST two-component regulatory systems?

a bacterium occupying an environment with heterogeneous resource supply

proteorhodopsin

a form of rhodopsin that allows cells to use light energy to drive ATP synthesis (found in marine heterotrophs)

commonly found in food products.

acetic acid bacteria

Which compounds serve as major sources of energy for ruminant animals?

acetic, butyric, and propionic acids

Nitrogen fixation results in the

addition of biologically available N to an ecosystem.

Most methanotrophs are obligate ________ because ________.

aerobes / the initial step of methane oxidation requires O2

Winogradsky columns are used primarily for enrichment of

aerobes, anaerobes, and phototrophs

Anoxygenic phototrophs

can be either autotrophic or heterotrophic and may use a variety of electron donors for photosynthesis

Whether an organism is classified as a photoheterotroph or a chemolithotroph depends on its

carbon and energy sources

The Ca cycle is tightly coupled to the

carbon cycle through calcium carbonate formation in ocean waters.

Whether an organism is classified as a photoheterotroph or a photoautotroph depends on its

carbon source

Whether an organism is classified as an autotroph or a heterotroph depends on its

carbon source

A species of insect that lives solely on pine sap was found to contain a bacterial symbiont. Genome sequencing of both the host and the symbiont revealed that the symbiont lacked many genes required for energy production, and the host lacked genes for biosynthesis of several essential amino acids. What is/are the most likely mechanism(s) that caused the loss of these genes?

coevolution

Horizontal gene transfer

complicates the construction of phylogenetic trees and the interpretation of specific traits in relation to evolution.

In which of the following environments would you expect to find a high number of iron-reducing bacteria?

deep subsurface

paradox of mutualism evolution

defined as the persistence of interspecific cooperation, despite the potential advantages of cheating

By isolating total community RNA, using reverse transcriptase to make cDNA copies of it, and then sequencing the cDNA, ecologists can

determine the community genome expression at the moment of sampling

commonly found across diverse microbial taxa.

diazotrophs

In Bacteria, a chromosome can be distinguished from a plasmid, because a chromosome is a genetic element that

encodes for essential functional genes.

Whether an organism is classified as a phototroph or a chemotroph depends on its

energy source

The methodology of microbial ecology includes

enrichment and isolation of specific microbes, cell-staining, and gene, transcript, and protein characterization.

Transcription of chaperonins is greatly accelerated when a cell is stressed by

excessive heat.

Aside from using light as a source of energy, another important part of the functional diversity of some bacterial phototrophs is their ability to

fix nitrogen gas

The higher the genotypic diversity in a microbial population living in heterogeneous environmental conditions, the more variable the ___________ among individual microbes.

flexible genome

Metatranscriptomics and metaproteomics are favored over metagenomics when ________ is of more interest than ________.

function or gene expression / gene presence

Functional traits can be shared between organisms with divergent SSU rRNA sequences because

functional traits may evolve independently, be shared through horizontal gene transfer, or be lost in divergent lineages.

Microenvironments and environmental heterogeneity are responsible for

generating microbial diversity

For a given microbial species, ___________ are considered a part of the pan genome, while ___________ are considered a part of the core genome.

genes carried on plasmids / highly conserved genes

In contrast to bacterial endospores, fungal spores LACK ________ resistance.

heat

Ferrous iron (Fe2+) oxidation generally occurs in environments with

high H+ concentrations. (acidic)

Low gene frequencies are maintained in bacterial populations due, in part, to

high rates of gene turnover.

What characteristics make a gene a good candidate for determining the evolutionary relationships between organisms?

highly conserved but also contains variable regions

High gene frequencies are maintained in bacterial populations due, in part, to

homologous recombination

The pan genome of a microbial species is constantly changing because of

horizontal gene transfer

Widespread antimicrobial drug resistance is usually passed by

horizontal gene transfer

Which of the following processes does NOT result in increased carbon sequestration A) Increased soil aggregation B) increased recalcitrance of carbon C) increased nitrogen supply for increased heterotrophic activity D) increased carbon fixation by photosynthesis

increased nitrogen supply for increased heterotrophic activity

Which of the following pairs of microorganisms are NOT likely to form close associations or consortia? A) purple sulfur bacteria and dissimilative sulfur-reducers B) dissimilative sulfur-reducers and dissimilative sulfur-oxidizers C) nitrogen-fixing cyanobacteria and fungi D) nitrogen-fixing cyanobacteria and dissimilative sulfate-reducers

nitrogen-fixing cyanobacteria and dissimilative sulfate-reducers

The phylogenetic trees of the nifH and SSU rRNA genes are incongruent because

of horizontal gene transfer.

Nitrification and anammox both

oxidize ammonia, but nitrification uses O2 and anammox uses NO2- for electron acceptors.

Whether an organism is classified as an aerobe or anaerobe depends on its

oxygen source

Microenvironments of soil exist where ________ concentrations greatly vary.

oxygen, nitrate, and sulfur

As oxygen appeared in the atmosphere, ________ also accumulated, which formed a protective barrier that protects the Earth from ________.

ozone/ UV radiation

________ are the main primary producers in freshwater environments

phototrophic microorganisms

The evolutionary history of a group of organisms is called its ________ and it is inferred from ________.

phylogeny / nucleotide sequence data

Dissimilatory sulfideoxidizers use a variety of unique ecological strategies in order to

position themselves at interfaces where sulfide and oxygen meet

Dissimilatory sulfide-oxidizers use a variety of unique ecological strategies in order to

position themselves at interfaces where sulfide and oxygen meet.

What is different about nutrient cycling in freshwater vs. saltwater marshes?

presence of sulfate impacts anaerobic processes in saltwater marshes but not freshwater wetlands

Piezophilic

pressure loving

Which feature(s) differentiate(s) Actinobacteria from Firmicutes?

relative G+C content in their genomes (example: high vs. low GC content)

The rRNA gene sequences of hyperthermophilic Archaea and Bacteria have diverged ________ over time, likely due to ________.

relatively little / strong constraints on sequence changes at higher temperatures

Most nitrogen-fixing bacteria symbiotically associated with plants are called

rhizobia.

Evidence of ________ supports the hypothesis that eukaryotes are derived from bacteria.

ribosome contents and DNA content in the nucleus

Metagenomics involves the analysis of a microbial community by

sampling and sequencing all of the genes in an environment

Microbial diversity is thought of in terms of phylogenetic diversity and functional diversity because

similar functional traits are often found in divergent phylogenetic groups.

Greenhouse gases

such as CO2, CH4, and N2O trap infrared radiation and heat the Earth.

Some nitrifying prokaryotes carry out metabolic cooperation by a process known as

syntrophy.

Which of the following genomic techniques would provide information on microbial functional potential of a mixed microbial community?

transcriptomics

Enzyme induction occurs

when the substrate is present.