Exam 26: Bacteria and Archaea

Which of the following is the MOST likely way that scientists first identified streptomycetes?

What is one advantage of fermentation over cellular respiration in certain environments?

Horizontal gene transfer can happen through:

A researcher synthesizes a new drug that specifically targets and degrades peptidoglycan. What type of infections could this drug treat?

Many antibiotics that target bacteria are effective against Archaea.

Conjugation is a type of horizontal gene transfer that relies on a structure known as a pilus to bring two cells into close enough contact to transfer genetic material.

A woman visits her doctor complaining of stomach pain and is diagnosed as having a stomach ulcer. If the doctor were to assess the microbial composition of the woman's stomach, what might he expect to find?

Nodules found on the roots of leguminous plants like soybeans harbor bacteria that fix nitrogen. These nodules are an example of the intimate and specialized partnerships that have been established over time between prokaryotes and eukaryotes. Coevolution maintains these types of relationships since both participants benefit. Plants receive biologically useful forms of nitrogen needed for growth, and the bacteria reside in an oxygen-free environment required by enzymes involved in the nitrogen-fixing process. Humans also maintain intimate associations with beneficial bacteria and even archaea! In fact, the prokaryotic cells in and on human bodies outnumber the eukaryotic human cells by tenfold according to some estimates. These microbial inhabitants help humans digest food, provide essential vitamins absorbed by the intestines, and even impact the immune system. The microbes that coevolve with plants arrive by infection of root tissue. The microbiota that coevolve with humans colonize human tissues after birth. Below is a chart showing the distribution of the gut microbiota in a human female. Panels (a) and (b) below depict two scenarios for the distribution of the gut microbiota in her son. The son maintains a similar diet in both scenarios and has not undergone recent antibiotic treatment (which would decimate and/or alter the entire gut community). Which of the two scenarios supports the hypothesis that microbiota in the son arrive by infection? Which suggests the microbiota are inherited by offspring?

Consider the chemical reactions of the sulfur cycle shown in Figure 26.10. Reduction of CO₂ to generate carbohydrates can occur when coupled to the oxidation of reduced sulfur compounds (e.g., H₂S). This latter process is carried out by what type of microorganism(s)?

Oxygen is generated during a reaction if the process is:

Fermentation can be performed only by bacteria and not by archaeons.

Autotrophs produce carbohydrates by reducing CO₂, whereas heterotrophs synthesize carbohydrates by ingesting smaller preformed organic compounds like glucose.

If you were to analyze the deepest layer of a microbial mat along a coastline (i.e., the layer farthest away from the surface of the water), you would find that H₂S levels sharply increase, as do the numbers of chemoautotrophic microorganisms.

The totality of microbes that reside in/on humans, the genomes of these microbes, and environmental interactions between the microbes and their human host are known as:

A doctor takes two different cheek swabs from one of his patients. He cultures the microorganisms from one swab and derives microorganism sequence information from the other. What do you expect his results will be?

During _____, N₂ within the atmosphere is converted to NH₃. Primary producers can then use the nitrogen from NH₃ to build organic compounds.

Clostridium difficile is a bacterium that is often found in the gastrointestinal tract of healthy individuals. It is also a common cause of hospital-acquired infections. Most individuals who become ill with C. difficile do so following antibiotic treatment. This information suggests that C. difficile:

Knowledge of the nucleotide sequence for the gene encoding the small subunit of the ribosomal RNA (rRNA) provides little information about the metabolic capabilities of microorganisms found in soil and seawater other than what can be inferred from sequence similarity to 16S rRNA genes from cultured species.

Instead of being isolated by pure culture, SAR11 was discovered when researchers analyzed the gene sequences contained within seawater samples.

A biologist draws a tree of life having only three branches. Which of the following groups did the biologist MOST likely choose for her diagram?