Chapter 27: Archaea and Bacteria (Part 2, Week 5)

Question 1

[Start 27.3 Reproduction]

T/F Bacteria and archaea do not engage in the process of sexual reproduction used by eukaryotes, involving specialized gametes, gamete fusion, and
meiosis.

Answer 1

True

Question 2

How do bacteria and archaea usually reproduce?

Answer 2

Asexually.

Generally by means of a type of cell division known as binary fission, but sometimes by forming small
cells, known as buds, from one end.

In addition, some bacteria produce tough cells that can withstand deleterious conditions for long
periods in a dormant condition.

Question 3

What is binary fission?

Answer 3

The process of cell division in bacteria and archaea in which one cell divides into two cells.

When sufficient nutrients are available, an entire population of identical cells can be
produced from a single parental cell by repeated binary fission.

This growth process allows microbes to become very numerous in water, food, or animal tissues, potentially causing harm.

Question 4

How is the division of a bacterial cell viewed by?

Answer 4

Scanning electron microscopy

When samples are spread onto the surfaces of laboratory dishes containing nutrients, single
cells of bacteria or archaea may divide repeatedly to form visible colonies, which can be easily counted.

The number of colonies is an estimate of the number of culturable cells in the original sample.

If a fluorescence microscope is available, cells can be counted directly by applying a fluorescent stain that binds to their DNA. Each cell glows brightly when illuminated with UV light.

Question 5

What is the basis of a widely used method for detecting and counting bacteria in food, water samples, or patients’ body fluids?

Microbiologists who study the spread of disease need to quantify bacterial cells in samples taken from the environment.

Medical technicians often need to count bacteria in body fluid samples to assess the likelihood of infection.

Answer 5

Binary fission

Question 6

Since bacterial cells are small and often unpigmented, they are difficult to count directly, what is one way microbiologists count bacteria?

Answer 6

Place a measured volume of sample into
laboratory dishes filled with a semisolid nutrient medium.

Bacteria in the sample undergo repeated binary fission to form colonies of cells visible to the unaided eye.

Because each colony represents a single cell that was present in the original sample, the number of colonies in the dish reflects the number of living bacteria in the
original sample.

The other way is the use of stains and UV light previously talked about.

Question 7

When is the flourescense method used?

Answer 7

The fluorescence method must be used when the microbes of interest cannot be cultivated in
the laboratory. For many bacteria and archaea, the conditions needed to foster population growth in the laboratory are not known.

Question 8

When do some bacteria produce thick-walled cells that are able to survive unfavorable conditions in a dormant state?

Answer 8

These specialized cells develop when bacteria have experienced stressful conditions, such as low nutrients or unfavorable temperatures.

Such dormant cells may be able to germinate
into metabolically active cells when conditions improve again.

For example, aquatic filamentous cyanobacteria often produce akinetes, thick-walled, food-filled cells, when winter approaches.

Akinetes are able to survive winter at the bottoms of lakes, and they produce new filaments in spring when they are carried by water currents to the
brightly lit surface.

Persistence of such akinetes explains how
harmful cyanobacterial blooms can develop year after year in overly fertile lakes.

Question 9

What is a structure with a tough coat that is produced inside of certain bacteria and then released when the enclosing bacterial cell dies and breaks down?

What are two examples of bacteria that creates endospores?

Answer 9

Endospores.

This typically contains DNA and other materials.

Endospores can remain alive, though in a
dormant state, for long periods, then reactivate when
conditions are suitable.

For example, Bacillus anthracis causes the disease anthrax and is thus a potential agent in bioterrorism and germ warfare. Most cases of human anthrax result when endospores of B. anthracis enter breaks in the skin, causing skin infections that are relatively easily cured by antibiotic treatment.

Clostridium botulinum can contaminate improperly canned food that has not been heated
to temperatures high enough to destroy its tough endospores.

When the endospores germinate and bacterial cells grow in the food, they produce a deadly toxin, as well as NH3 and CO2 gases, which cause can lids to bulge. If humans consume the food, the toxin causes botulism, a severe type of food poisoning that can lead to respiratory and muscular paralysis.

Question 10

What is a really interesting fact about botulism toxin created by the bacteria, Clostridium botulinum?

Answer 10

The botulism toxin is marketed commercially as Botox, which is injected into the skin, where it paralyzes facial muscles, thereby reducing the appearance of wrinkles.

The toxin has also been used as a migraine treatment.

Clostridium tetani produces a nerve toxin that causes lockjaw, also known as tetanus, when bacterial cells or endospores from soil enter wounds. The ability of the genera Bacillus and Clostridium to produce resistant endospores helps explain their widespread
presence in nature and their effect on humans.

Question 11

[Start 27.4 Nutrition and Metabolism]

T/F All living cells require energy and a source of carbon to build their organic molecules.

Answer 11

True

Question 12

T/F Bacteria and archaea use one strategy to obtain energy and carbon for growth.

Answer 12

False. They use many.

Question 13

How are the microbes classified?

Answer 13

• Their energy source
• Carbon source
• Response to oxygen
• Presence of specialized metabolic processes

Question 14

What is an organism that has metabolic pathways that use energy from either inorganic molecules or light to make organic molecules?

Answer 14

Autotrophs (Greek meaning self feeder)

Organisms that are able to produce allor most of their own organic molecules from inorganic sources.

Question 15

What are the two categories that autotrophs fall under?

Answer 15

Photoautotrophs and Chemoautotrophs

Question 16

What is a type of autotroph that is an organism that uses the energy from light to make organic molecules from inorganic sources?

Answer 16

Photoautotroph

Including cyanobacteria, use light as a source of energy for the synthesis of organic molecules from CO2 and H2O or H2S.

Question 17

What is a type of autotroph that is an organism able to use energy obtained by chemical modifications of inorganic compounds to synthesize organic compounds?

Answer 17

Chemoautotrophs

Such chemical modifications include nitrification (the conversion of ammonia to nitrate) and the oxidation of sulfur, iron, or hydrogen.

For example, archaea of the genus Sulfolobus
can oxidize certain sulfur-containing minerals.

Question 18

What are organisms that cannot produce their own organic molecules by using energy from inorganic sources or light; they must obtain one or more organic compounds from their environment?

Answer 18

Heterotrophs

Question 19

What are the two types of heterotrophs and what do they mean?

Answer 19

Photoheterotrophs - An organism that is able to use light energy to generate ATP but must take in organic compounds from the environment as a source of carbon.

Chemoheterotrophs - An organism that must obtain organic molecules both for energy and as a carbon source.

Question 20

What are organisms that require oxygen for survival?

What about organisms that don’t require oxygen for survival?

Answer 20

Obligate aerobes (most eukaryotes to include humans)

Obligate anaerobes, such as the Firmicutes genus
Clostridium, are poisoned by O2.
.

Question 21

How are people suffering from gas gangrene (caused by Clostridium perfringens and related species) treated?

This species is a obligate anaerobe.

Answer 21

Usually treated by placement in a chamber having a high oxygen content (calleda hyperbaric chamber), which kills the organisms and deactivates the toxins.

Question 22

What is a microorganism that does not use oxygen but is not poisoned by it either?

Answer 22

Aerotolerant anaerobe

These organisms obtain their energy by fermentation or anaerobic respiration.

Anaerobic metabolic processes includedenitrifi cation (the conversion of nitrate into N2 gas) and the reduction of manganese, iron, and sulfate, which are all important in the Earth’s cycling of minerals.

Question 23

What is a microorganism that can use oxygen in aerobic respiration, obtain energy via anaerobic fermentation, or use inorganic chemical reactions to obtain energy?

Answer 23

Facultative anaerobe

One fascinating example of a facultative anaerobe is the species Thiomargarita namibiensis, a large proteobacterium.

This chemoheterotroph obtains its energy in two ways: by oxidizing sulfide with oxygen when oxygen is available or, when oxygen is low or unavailable, by oxidizing sulfide with nitrate.

In either case, the cells convert sulfide to elemental sulfur, which is stored within the cells in large globules.

Question 24

What is a specialized metabolic process in which certain prokaryotes use the enzyme nitrogenase to convert inert atmospheric nitrogen gas (N2) into ammonia (NH3); also, the industrial process by which humans produce NH3 fertilizer from N2?

Answer 24

Nitrogen fixation

The removal of nitrogen from the gaseous phase is called fixation, and microbes that perform this process are known as nitrogen fixers.

Question 25

What do plants and algae use to produce proteins and other essential nitrogen-containing molecules that is an important component of the cycling of nitrogen on a global basis?

Answer 25

Ammonia (NH3; not N2 (inert nitrogen gas))

This is why nitrogen fixation is so important.

As a result, many plants have developed close relationships with nitrogen fixers, which provide ammonia fertilizer to their plant partners.

In addition to the aquatic photosynthetic cyanobacteria mentioned in the chapter opening, many types of heterotrophic soil bacteria also fix nitrogen.

Question 26

What is nitrogenase inhibited by?

Answer 26

O2 or oxygen.

Most nitrogen fixers conduct nitrogen fixation only in low-oxygen conditions. Many cyanobacteria generate low-oxygen conditions in specialized cells known as heterocytes, allowing nitrogen fixation to occur in these cells.

Question 27

How do heterocytes display adaptions that reduce nitrogenase exposure to oxygen?

Answer 27

These include thick walls that reduce inward O2
diffusion, increased occurrence of cellular reactions that consume oxygen, and down-regulation of the oxygen-producing components of photosynthesis.

The latter adaptation, involving reduction in chlorophyll synthesis, explains why heterocytes are paler in color than neighboring photosynthetic cells.

Question 28

[Start 27.5 Ecological Roles and Biotechnology Applications]

Who produces and breaks down organic carbon which is important in the global carbon cycle?

Answer 28

Archaea and bacteria.

Bacteria function as beneficial symbionts in plants and animals and as disease agents.

Question 29

What is the Earth’s carbon cycle?

Answer 29

Sum of all the chemical changes that occur among compounds that contain carbon.

Question 30

What is one way bacteria and archaea influence the Earth’s carbon cycle?

Answer 30

By producing and consuming methane.

Question 31

What is the major component of natural gas, which is a greenhouse gas, and is more powerful than CO2?

Answer 31

Methane (CH4)

CH4 increases global warming over 20 times more per molecule than does CO2

Therefore, atmospheric CH4 has the potential to alter the Earth’s climate, and in recent years the level of CH4 has been increasing in Earth’s atmosphere as the result of human activities.

Question 32

What are several groups of anaerobic archaea that convert CO2, methyl groups, or acetate to methane, and release it from their cells?

Answer 32

Methanogens

These typically live in swampy wetlands, in deep-sea habitats, or in the digestive systems of animals, including cattle and humans.

Marsh gas produced in wetlands is largely composed of CH4, and large quantities of CH4 produced long ago are trapped in deep-sea and subsurface Arctic deposits.

Question 33

What are aerobic bacterium that consumes methane?

Answer 33

Methanotrophs

They reduce the concentration in the atmosphere.

In the absence of methanotrophs, Earth’s atmosphere would be muchricher in the greenhouse gas CH4, which would substantially increase global temperatures.

Question 34

T/F Bacteria and archaea are also important in producing and degrading complex organic compounds.

Answer 34

True

Question 35

What is an organism that synthesizes the organic compounds used by other organisms for food?

Answer 35

Producers

Cyanobacteria and other autotrophic bacteria.

Such bacteria, together with algae and plants, remove CO2 from the atmosphere and, via photosynthesis, synthesize the organic compounds that are used by themselves and other organisms for food.

Question 36

What is an organism that gets its energy from the remains and waste products of other organisms?

Answer 36

Decomposers (AKA saprobes)

Heterotrophic microorganisms (as well as fungi and animals)

These organisms break down dead organisms and organic matter, releasing minerals for uptake by living things. Astonishingly, many bacteria are able to break down antibiotics for use as a source of organic carbon

Question 37

What is an intimate association between two or more organisms of different species?

Answer 37

Symbiosis (like many bacterial species)

Many live in mutualism. Some cause death or harm to each other.

Bioluminescent bacteria that have the ability to produce and emit light often form symbiotic relationships with squid and other marine animals.

Question 38

What is a virus or microorganism that causes disease symptoms in its host?

Answer 38

Pathogen

Cholera, leprosy, tetanus, pneumonia, whooping cough, diphtheria, Lyme disease, scarlet fever, rheumatic fever, typhoid fever, bacterial dysentery, and tooth decay are among the many examples of human diseases caused by bacterial pathogens.

Bacteria also cause many plant diseases of importance in agriculture, including blights, soft rots, and wilts.

Question 39

What are the four steps that Germin physician Robert Koch developed to determine whether a particular organism causes a specific disease? (4)

What is the name of these steps?

Answer 39

1. The presence of the suspected pathogen must correlate with occurrence of symptoms.
2. The pathogen must be isolated from an infected host and grown in pure culture if possible.
3. Cells from the pure culture should cause disease when in oculatedinto a healthy host.
4. The same pathogen should be isolatable from the second infectedhost.
5. Koch’s postulates - A series of steps used to determine whether a particular organism causes a specific disease.

Question 40

What do you call the proteins that are injected by gram-positive pathogenic bacteria in plant and animals cells as part of the infection process by using needle -like systems?

Answer 40

Injectisomes (made of components also found in flagella)

Examples of bacteria whose injectisomes allow them to attack human cells are Yersinia pestis (the agent of bubonic plague), Salmonella enterica (which causes the food poisoning called salmonellosis), and Burkholderia pseudomallei (the cause of melioidosis,a deadly disease of growing concern in some parts of the world).

More than 20 million people are infected by means of injectisomes every year. Several plant pathogenic bacteria also infect cells by means of injectisomes.

Question 41

What other gram-negative bacteria synthesize a of system which functions as a channel to deliver toxins or DNA into cells?

Answer 41

Type IV secretion system

Question 42

What is the leading cause of acute kidney failure in children?

Answer 42

E. coli

Question 43

Fun Fact:

Several industries have harnessed the metabolic capabilities of microbes obtained from nature.

The food industry uses bacteria to produce chemical changes in food—for example, to make dairy products, including cheese and yogurt, from milk.

Cheese makers add pure cultures of certain bacteria to milk. The bacteria consume milk sugar(lactose) and produce lactic acid, which aids in curdling the milk.

The chemical industry produces materials such as enzymes, vinegar, amino acids, vitamins, insulin, vaccines, antibiotics, and other useful pharmaceuticals by growing particular bacteria in giant vats.

For example, the hot springs bacterial species
Thermus aquaticus is a source of a form of DNA polymerase widely used in biology laboratories to amplify DNA in polymerase chain reaction (PCR).

Industrially grown bacteria produce the antibiotics streptomycin, tetracycline, kanamycin, gentamycin, bacitracin, polymyxin-B, and neomycin.

Answer 43

The field of synthetic biology utilizes bacteria as chemical factories by genetically modifying bacterial genomes so that the bacteria produce particular useful compounds, such as pharmaceuticals and renewable biofuels.

For example, biologists have modified the genome of the bacterium Caldicellulosiruptor bescii so it can transform switchgrass into ethanol.

The ability of some microorganisms to break down organic compounds or precipitate metals makes them very useful in treating wastewater, industrial discharges, and harmful substances such as explosives, pesticides, and oil spills.

Agriculture employs several species of Bacillus, particularly B.thuringiensis (Bt), which produce toxins that kill the insects that ingest them but are harmless to many noninsect species.

Tent caterpillars, potato beetles, gypsy moths, mosquitoes, and black flies are among the pests that can be controlled by the Bt toxin. For this reason, toxin-encoding genes from B. thuringiensis
have been cloned and introduced into some crop plants, such as corn and cotton, to reduce conventional pesticide use and increase crop yields.

Question 44

What is the use of living organisms, usually microbes or plants, to detoxify polluted habitats such as dump sites or oil spills?

Answer 44

Bioremediation