ch. 27 (bacteria and archaea)

TORF: Data showing that the Bacteria were the first lineage to diverge from the common ancestor of all living organisms suggest that the Archaea and Eukarya are more closely related to each other than they are to the Bacteria.

true

Bacteria are extremely diverse in structure and in how they obtain energy and nutrients. This diversity enables bacteria to live in a wide variety of environments.

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Fast foods, cookies and ice cream, sodas and energy drinks -- Americans eat a lot of processed foods high in fats and simple sugars. Not surprisingly, this type of diet can lead to weight gain and is one of the main culprits in the obesity epidemic in this country. But, is there more to this story? The foods you eat serve as food for the community of microorganisms that inhabit your digestive tract. Those microbes have their own food "preferences," metabolizing different types of food molecules and releasing their byproducts, which your body may absorb. Scientists have hypothesized that a high-fat, high sugar diet actually alters the composition of the microbial community that inhabits the beginning of the large intestine, which contributes to obesity. Because of the difficulties of carrying out experiments on humans, scientists have used mice as an animal model in which to test this hypothesis.

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Plantlike photosynthesis that releases O2O2 occurs in

cyanobacteria

Part A (Gram Staining) --- Classify each statement or picture as applying to gram-positive bacteria, gram-negative bacteria, or both. • gram-positive bacteria: • gram-negative bacteria: • both:

• gram-positive bacteria: have a thick peptidoglycan layer; appear purple after Gram staining; alcohol rinse does not remove crystal violet • gram-negative bacteria: have a thin peptidoglycan layer; have an outer membrane as part of their cell wall structure; appears pink after Gram staining; alcohol rinse easily removes crystal violet • both: have a plasma membrane --- (Gram staining is a technique for classifying bacteria based on differences in the structure of their cell walls. Gram-negative bacteria and gram-positive bacteria both have a plasma membrane surrounded by a cell wall that contains peptidoglycan. However, the cell wall of gram-negative bacteria is composed of a thin layer of peptidoglycan and an outer membrane, whereas the cell wall of gram-positive bacteria is composed of a thick layer of peptidoglycan. Gram-negative bacteria appear red or pink because the alcohol rinse washes away the crystal violet dye. Gram-positive bacteria appear purple because the alcohol rinse does not wash away the crystal violet dye.)

Part A(Reviewing Binary Fission in Bacteria): The figure shows how bacteria reproduce through binary fission. --- Drag the terms on the left to the appropriate blanks on the right to complete the sentences. 1.) Binary fission is a form of _____ because a single individual is the sole parent and passes copies of all its genes to its offspring. 2.) During binary fission, DNA replication begins at the _____ and continues all the way around the circular chromosome. 3.) When DNA replication is complete and the bacterium has reached twice its original size, the _____ grows inward, dividing the parent cell into two daughter cells. 4.) In theory, the two daughter cells are _____ each other and the parent cell. 5.) However, mistakes made during DNA replication sometimes result in _____, changes to the nucleotide sequence of DNA. 6.) The rapid reproduction and large population sizes of many bacterial populations mean that even a small mutation rate can lead to considerable _____.

1.) asexual reproduction 2.) origin of replication 3.) plasma membrane 4.) genetically identical to 5.) mutations 6.) genetic variation --- (Bacteria reproduce through binary fission. • During binary fission, the DNA in the bacterial chromosome is replicated, and one copy is passed to each daughter cell. • Although plasmids (small, circular DNA molecules separate from the main bacterial chromosome) are not shown in the figure, any plasmids in a bacterial cell are also replicated and passed to each daughter cell during binary fission. • Mutations that arise during DNA replication are one source of genetic variation in bacterial populations. • The rapid reproduction and large sizes of many bacterial populations can yield considerable genetic variation despite a low mutation rate.)

What is lateral gene transfer?

Physical transfer of a gene from a species in one lineage to a species in another lineage. (Lateral gene transfer is the physical transfer of a gene between distantly related lineages.)

Which group was not described in Woese's tree of life analysis?

Prokarya

What is the function of fimbriae?

They are used to attach the cell to its substrate or to other prokaryotes. --- (They are hair-like projections that aid in attachment. They are also known as attachment pili to distinguish them from the pili used in conjugation.)

How does a large amount of genetic variation observed in prokaryotes arise?

They have extremely short generation times and large populations. They also can exchange DNA with many types of prokaryotes by way of horizontal gene transfer. --- (The short generation times and large population sizes in most prokaryotic species, coupled with their ability to exchange genes, helps to increase genetic variability beyond what we would expect in asexually reproducing organisms.)

Part C (Making Predictions): Is the microbial community in the intestine a key to understanding obesity? To explore this question, scientists conducted another experiment. The scientists hypothesized that the microbial community of obese mice is more efficient at extracting energy from food, thus providing more calories to the host, and that it promotes more fat deposition than does the microbial community of lean mice. They decided to test this hypothesis by transplanting microbes from an obese donor mouse into lean mice. For this experiment, the scientists randomly divided lean germ-free mice into two groups. The experimental group received microbes from a genetically obese donor (the donor's obesity was due to genetic factors, not diet). The control group received microbes from a genetically lean donor. Both groups were fed the same low-fat, high-fiber diet. After two weeks, the scientists measured the increase in body fat in the mice. They also determined the amount of energy (in kcal/g) in the feces of both groups -- that is, the energy in the food molecules that was not extracted or absorbed by the mice. ---

When this experiment was performed, the results supported the scientists' hypothesis: • Mice that received microbes from an obese donor (the experimental group) had a significantly greater increase in body fat than the mice that received microbes from a lean donor (the control group). • The mice that received microbes from the obese donor also had less energy (fewer kcal/g) in its feces. The microbial community had wrung more energy out of the food molecules, thus making more calories available to the mice. Do these results mean that obesity can be overcome by a few simple tweaks to the microbial community? Probably not. To understand a complex system -- and the interactions of hundreds of species of microbes with each other and with the human body are certainly complex -- scientists must isolate and study one small piece of the puzzle at a time. Many more years of research will be needed for definitive answers about the relationship of our microbial inhabitants to obesity.

Which of the following statements about phylogenetic trees is true? a.) A paraphyletic group consists of a common ancestor and some of its descendants. b.) A paraphyletic group consists of an ancestral population and all of its descendants. c.) A paraphyletic group has not experienced lateral gene transfer. d.) A monophyletic group consists of a common ancestor and some of its descendants.

a (This statement is true; the common characteristics of a paraphyletic group may have arisen from lateral gene transfer to some, but not all, lineages.)

Drag the labels to their appropriate locations on the concept map below to explore the links between antibiotic resistance, binary fission, and conjugation.

a.) antibiotics b.) antibiotic resistant c.) binary fission d.) conjugation e.) mutations f.) DNA replication g.) genetic recombination h.) genetic variation --- (Antibiotic resistance in bacterial populations has followed close upon the heels of the widespread use of antibiotics. • As antibiotic-resistant bacteria thrive and sensitive bacteria die, the proportion of resistant cells in a population increases dramatically. These resistant cells continue to undergo binary fission, resulting in an infection that is difficult to treat. • The ability of bacterial populations to evolve resistance requires genetic variation. • Mutation is one source of genetic variation. The large population sizes and rapid reproduction of bacterial populations means that even with a low mutation rate, a significant number of mutations are seen in bacterial populations. Some of these mutations contribute to antibiotic resistance. • Processes such as conjugation allow for genes to be exchanged among bacteria. Because conjugation can occur between bacterial cells of the same species or of different species, antibiotic resistance sometimes spreads surprisingly easily from one species of bacteria to another. • A single R plasmid may have genes that provide resistance to ten or more different antibiotics. This is especially problematic when bacteria that are serious health threats become resistant to multiple antibiotics. For example, methicillin-resistant Staphylococcus aureus (MRSA) infections are caused by bacteria that have evolved resistance to most of the antibiotics that were once used to treat staph infections. MRSA is becoming increasingly difficult to treat.)

Part B (Nutritional Modes of Bacteria): Label the diagram below to show the relationship between nutritional modes of bacteria. --- Drag the labels to their appropriate locations on the diagram.

a.) autotrophs b.) heterotrophs c.) chemoautotrophs d.) photoautrophs e.) photoheterotrophs f.) chemoheterotrophs g.)phototophs h.) chemotrophs --- (Some bacteria obtain energy from light (phototrophs), whereas other bacteria obtain energy from chemicals (chemotrophs). Autotrophs (literally "self-feeders") require only an inorganic substance, such as carbon dioxide, as their carbon source; heterotrophs (literally "other-feeders") require at least one organic nutrient as their carbon source.)

Select the correct statement about bacteria. a.) All organisms with cells containing a membrane-enclosed nucleus and organelles are eukaryotes, whereas all organisms with cells lacking a membrane-enclosed nucleus and organelles are bacteria. b.) Certain bacteria live within rocks kilometers below the Earth's surface. c.) The majority of bacteria cause human disease.

b (Amazing but true. Read about the diverse habitats of prokaryotes.)

Which statement is true about obligate anaerobes? a.) They will use O2 if it is present, but can obtain energy by fermentation if needed. b.) They are poisoned by O2. c.) They use O2 for cellular respiration and cannot grow without it. d.) They live exclusively by cellular respiration or by anaerobic respiration. e.) They obtain energy by oxidizing ferrous ions.

b (Some obligate anaerobes live exclusively by fermentation; others extract chemical energy by anaerobic respiration, in which substances other than O2 accept electrons at the "downhill" end of electron transport chains.)

Part B (Interpreting Experimental Results): After 8 weeks on the different diets, the scientists collected the following data on the two groups of mice: the amount of weight gained the amount of body fat the composition of the microbial community, especially the abundance of the two types of bacteria that dominate this region of the intestine -- Firmicutes and Bacteriodetes The results are shown in this data table. --- Which three statements are valid conclusions that can be drawn from these results? a.) A relative abundance of Bacteriodetes less than 25% results in obesity. b.) A high-fat, high-sugar diet results in greater weight gain than a low-fat, high-fiber diet. c.) A high-fat diet is more likely to cause obesity than a high-sugar diet. d.) A microbial community dominated by Firmicutes is associated with increased body fat. e.) Firmicutes cause obesity. f.) A high-fat, high-sugar diet alters the composition of the microbial community. g.) People who consume a high-fat, high-sugar diet will have increased body fat.

b, d, f (In this experiment, mice that were fed a high-fat, high-sugar diet gained more weight and more body fat than did mice fed a low-fat, high-fiber diet. A high-fat, high sugar diet was also associated with increased abundance of Firmicutes in the microbial community of the large intestine.)

Bacteria that live around deep-sea, hot-water vents obtain energy by oxidizing inorganic hydrogen sulfide belched out by the vents. They use this energy to build organic molecules from carbon obtained from the carbon dioxide in seawater. These bacteria are _____.

chemoautotrophs (They use inorganic molecules (in redox reactions) for energy, and carbon dioxide for carbon.)

The prokaryotic organisms most likely to be found living in salt ponds are the _____.

halophiles (These archaea live in salty environments such as the Dead Sea.)

Photoautotrophs use

light as an energy source and CO2 as a carbon source

Genes for the resistance of antibiotics are usually located __________.

on plasmids

What characteristics were used to classify organisms before Woese's tree of life analysis?

presence of a membrane-bound nucleus (Before the tree of life analysis, organisms were classified as prokaryotes if they lacked a membrane-bound nucleus or eukaryotes if they possessed a membrane-bound nucleus.)

Which molecule did Carl Woese study to produce his tree of life?

ribosomal RNA (Ribosomal RNA was the molecule used to produce Woese's phylogeny because it evolves slowly and is critical to the function of the ribosome, which serves the same function in all three domains in the tree of life.)

An ecological relationship between organisms of different species that are in direct contact can best be described as _____.

symbiotic

Bioremediation is _____.

the use of organisms to remove pollutants from the environment

Part A (Designing a Controlled Experiment): In one experiment, scientists raised mice in germ-free conditions so the mice lacked intestinal microbes. The mice were fed a low-fat diet rich in complex plant polysaccharides, such as cellulose, that are often called fiber. When the mice were 12 weeks old, the scientists transplanted the microbial community from the intestine of a single "donor" mouse into all of the germ-free mice. Then they divided the mice randomly into two groups and fed each group a different diet. • Group 1 (the control group) continued to eat a low-fat, high-fiber diet. • Group 2 (the experimental group) ate a high-fat, high-sugar diet. --- Identify the components of this experiment by dragging the labels into the appropriate bins. • factor being tested (independent variable): • factors controlled (kept consistent): • factors being measured (dependent variable):

• factor being tested (independent variable): diet • factors controlled (kept consistent): age of the mice; initial composition of the microbial community • factors being measured (dependent variable): change in body fat; weight gain; final composition of the microbial community --- (In this experiment, the scientists intentionally varied only one factor (called the independent variable) -- diet. They standardized, or controlled, all other factors that might differ between the two groups of mice, including age and the initial composition of the microbial community (both groups of mice received microbes from the same donor mouse). Consequently, any differences in weight gain, body fat, or microbial community (the dependent variables) between the two groups can be attributed to diet.)