Micro chapter 17: Microbial Symionts

Which of these is TRUE of an ectosymbiont?

a) It is always harmful to the host.

b) It is either harmful or beneficial to the host.

c) It is always beneficial to the host.

d) It is best described as a mutualistic relationship.

e) It is best described as a commensal relationship.

b) It is either harmful or beneficial to the host.

Which of these is true of a mutualistic relationship?

a) Neither organism benefits or is harmed by the relationship.

b) One member benefits and the other member is harmed.

c) One member benefits and the other member does not receive any benefit.

d) Both organisms benefit.

e) Both members are harmed from the relationship.

b) One member benefits and the other member is harmed.

What is an endophyte?

a) A parasite of a plant.

b) A parasite of an animal.

c) A symbiont that lives inside plant cells.

d) A member of the plant root rhizosphere.

e) A member of the intestinal tract microbial community.

A symbiont that lives inside plant cells.

Which of these is characteristic of the nitrogenase enzyme?

a) It is found in both prokaryotes and eukaryotes.

b) It converts dinitrogen to nitrate.

c) It requires hydrogen gas for activity.

d) It is irreversibly inactivated by oxygen.

e) It is found in all plant symbionts.

d) It is irreversibly inactivated by oxygen.

The red color of plant root nodules is due to this oxygen binding protein.

a) cytochrome c

b) flavoprotein

c) leghemoglobin

d) menaquinone

e) nitrate reductase

c) leghemoglobin

Once rhizobia enter the plant cell through the infection thread they undergo rapid multiplication and differentiation into pleomorphic nitrogen fixing cells called _____ .

a) shizonts

b) bacteroids

c) elementary bodies

d) reticulate forms

e) nitromorphs

b) bacteroids

The host-range specificity between specific legumes with specific rhizobia involves the tran-scriptional inactivation of the bacterial nod genes through the secretion of specific ___________ by the plant.

a) flavonoids

b) sugars

c) fatty acids

d) nucleotides

e) lactones

a) flavonoids

In order to make sufficient ATP for symbiotic nitrogen fixation, the plant supplies the symbionts with ____________ for energy production.

a) NADH

b) glucose

c) C3 acids

d) fatty acids

e) C4-dicarboxylic acids

e) C4-dicarboxylic acids

Which of these is TRUE of a lichen?

a) It is classified as a plant.

b) It is comprised of a fungus and usually an green alga.

c) It is comprised of a fungus and an archaeal symbiont.

d) It is a type of slime mold.

e) It is comprised of a protozoan and anarchaeal symbiont.

b) It is comprised of a fungus and usually an green alga.

The mycobiont of a lichen receives sugars from the photobiont as a benefit from this relationship while the photobiont receives _______________ from the mycobiont as a benefit.

a) amino acids

b) ATP

c) inorganic nutrients and protection from desiccation

d) protection from predation

e) vitamins and amino acids

c) inorganic nutrients and protection from desiccation

Lichens reproduce asexually by ___________, which are hyphal -packaged algae cells.

a) soredia

b) ascus

c) conidia

d) zygospores

e) sporozoites

a) soredia

What is the human microbiome composed of?

a) Microbes that live in the intestinal tract of humans.

b) All the microbes that cause disease in humans.

c) All microbes that live on or within the human body.

d) Microbes that contribute to the health of humans.

e) Microbes that live on human skin.

c) All microbes that live on or within the human body.

The most common inhabitants of the human skin are members of which phyla?

a) Proteobacteria and Bacteroidetes

b) Proteobacteria and Firmicutes

c) Bacteroidetes and Firmicutes

d) Firmicutes and Actinobacteria

e) Actinobacteria and Proteobacteria

d) Firmicutes and Actinobacteria

The vagina of women of child-bearing age has an acidic pH. This is due to the colonization by which organisms?

a) staphylococci

b) lactobacilli

c) Candida sp

d) Bacteroides sp

e) micrococci

b) lactobacilli

Which of these is the MOST abundant bacterial group in the colon?

a) members of the phylum Proteobacteria

b) the family Enterobacteriaceae

c) obligate anaerobes

d) facultative anaerobes

e) lactobacilli.

c) obligate anaerobes

The majority of Archaea found in the human intestinal tract are _____ .

a) sulfate-reducing bacteria

b) halobacteria

c) sulfide oxidizing bacteria

d) methanogens

e) fermenters

d) methanogens

Herbivores require microorganisms to help them with the digestion of this compound.

a) starch

b) glycogen

c) cellulose

d) proteins

e) nucleic acids

c) cellulose

Some herbivorous cecal fermenters obtain additional nutrients from their food sources by this method.

a) Regurgitating their food and chewing it again.

b) Retaining it in their large intestine for long periods of time.

c) Eating their feces.

d) Selectively eating certain plants.

e) Moving the cecal-digested food back to the small intestine for absorption.

c) Eating their feces

Which of these is TRUE of ruminants?

a) They possess a single stomach chamber and long cecum.

b) They are considered to be hindgut fermenters.

c) They are inefficient in the digestion of plant material.

d) They obtain nutrients from digestion carried out by rumen microorganisms.

e) They often consume their own feces.

d) They obtain nutrients from digestion carried out by rumen microorganisms.

Many of the rumen bacteria specialize in the breakdown of these macromolecules.

a) proteins

b) cellulose polymers

c) peptidoglycans

d) nucleic acids

e) fatty acids

b) cellulose polymers

Acetogenesis is the production of acetic acid from which material(s)?

a) lactate

b) pyruvate

c) carbon dioxide and hydrogen

d) oxaloacetate

e) glucose

c) carbon dioxide and hydrogen

Microbes in the rumen are very efficient at converting ____________ and _________ into amino acids.

a) ammonia and urea

b) glucose and pyruvate

c) starch and cellulose

d) fatty acids and acetate

e) pyruvate and lactate

a) ammonia and urea

When the diet of a ruminant is drastically changed from grass to a starch rich diet, the ruminant may become very ill or die because:

a) the microbes in the rumen cannot break down starch.

b) of the production of large amounts of acid, resulting in acidosis.

c) they lack a source of protein.

d) they are unable to regurgitate the starch as cud.

e) the starch is broken down very slowly and the rumen becomes clogged.

b) of the production of large amounts of acid, resulting in acidosis.

24) Most microbial symbionts of invertebrates are in this group.

a) yeast

b) Archaea

c) protozoa

d) algae

e) Bacteria

e) Bacteria

Scientist are able to make an insect symbiont free by this method.

a) Hatching insect eggs in a sterile environment.

b) Treating the insect with an antibiotic.

c) Mating the insect with a symbiont free insect.

d) Irradiating insect eggs.

e) Putting the insect on a different diet.

b) Treating the insect with an antibiotic.

How do primary endosymbionts of insects differ from secondary endosymbionts?

a) Primary endosymbionts provide the insect with nutrients.

b) Secondary endosymbionts protect the insect from harmful bacteria.

c) Secondary endosymbionts do not remain with the host after three or four generations.

d) Primary endosymbionts show evidence of co-speciation with the host insect.

e) Secondary endosymbionts can easily be cultured.

d) Primary endosymbionts show evidence of co-speciation with the host insect.

Which of the following is NOT a feature of a primary endosymbiont?

a) They all have reduced genomes.

b) They are found in specialized cells called bacteriocytes.

c) They provide the host with nutrients.

d) They are passed on maternally.

e) They are required for survival or fertility.

c) They provide the host with nutrients.

The bacterial genus ___________ is a secondary symbiont and is capable of changing the female to male ratio of an insect to primarily female.

a) Rickettsia

b) Wolbachia

c) Pseudomonas

d) Culex

e) Bordetella

b) Wolbachia

Lower termites feed primarily on wood and contain symbiotic:

a) bacteria in their intestine.

b) bacteria and archaeons in their intestine.

c) fungi in their intestine.

d) protozoa, bacteria, and archaeons in their intestine.

e) protozoa and fungi in their intestine.

d) protozoa, bacteria, and archaeons in their intestine.

Cellulose consumed by the lower termite is hydrolyzed by cellulases produced by _____ .

a) fungi

b) bacteria

c) archaeons

d) the termite

e) yeast

d) the termite

How do termites obtain nitrogen in their diet?

a) From digestion of proteins.

b) From digestion of nucleic acids.

c) From nitrogen fixing bacteria in their gut.

d) From urea.

e) From nitrogen fixing protozoa.

c) From nitrogen fixing bacteria in their gut.

The hydrogen and carbon dioxide produced in the gut of the lower termite are used to produce __________ by symbiotic microbes.

a) methane

b) lactate

c) fatty acids

d) amino acids

e) glucose

a) methane

Which of these contains zooxanthellae as photosynthetic symbionts?

a) shipworms

b) termites

c) lichens

d) coral

e) tubeworms

d) coral

Most microbe-host relationships are harmful.

False

The nitrogenase enzyme is irreversibly inactivated by hydrogen.

False

Bradyrhizobium japonicum will form nodules on soybeans but not on peas, alfalfa, or beans.

true

Once rhizobia enter into the plant cell and differentiate they will not proliferate again.

true

Plaque on human teeth is considered a biofilm

true

The human colon contains more microbial cells than human cells that make up the entire body.

true

Intestinal microorganisms are important for the proper functioning of the immune system.

true

Hindgut fermenters have greater fermentation efficiency than ruminants.

false

Most endosymbionts of invertebrates can easily be cultured.

false

A group of microorganisms that are interdependent on one another for the stability of the com-munity is called a/an__________________

consortium

The type of symbiotic relationship in which one member benefits and the other member is not affected is called _________________.

commensalism

Endophytes are microorganisms that live within the tissue of ___________.

plants

All microorganisms that live on or within the human body are referred to collectively as the human ________________.

microbiome

The heaviest colonized area of the human body is the __________.

colon

Describe the process of rhizobial recognition of its host legume for the initiation of nodule formation.

Rhizobial species have a specific host range of legumes they can infect. The recognition process is controlled at the genetic level through plant stimulated induction of nodulation genes (nod) in the rhizobia. Specific flavonoid compounds are excreted by legumes that will be detected by their specific symbiotic rhizobial species. The flavonoid will activate the expression of nod genes. One of the nod genes encodes for the Nod factor, which is excreted by the bacterium to stimulate the plant root hair to curl around the bacterium. Once attached, the bacterium is able to invade the plant root through an infection thread that is formed by the plant.

Describe the process of rumen fermentation and nutrient acquisition by ruminants.

Ruminants are very efficient at extracting nutrients from plant material because the plant materi-al is first digested in the rumen by a consortium of microorganisms. After this initial digestion, the fermented material, including the microorganisms, moves through the stomach, small intes-tine, cecum and large intestine for further digestion and absorption of nutrients. The ruminant obtains nutrients from the digestion of rumen microbes and their fermentation products as the rumen fluid passes through the digestive system. Thus the initial fermentation in the rumen has considerable nutritional benefits for the ruminant. The ruminant does not chew, but swallows, plant material that moves to a chamber called the reticulum. Particulate material from the rumen is moved to the reticulum to form a slurry with the plant material called a cud. The cud is regur-gitated and chewed by the ruminant to form a fine paste which is swallowed and enters the ru-men for fermentation by the microbes present. After fermentation the rumen fluid flows into the omasum for quick absorption of electrolytes and water. From the omasum the fluid moves to a true stomach for digestion by acids and enzymes, before moving on to the small intestine and large intestine for further digestion and absorption of nutrients.

Describe the characteristics of a primary endosymbiont.

Primary endosymbionts have been evolving along with their host for thousands of years and show signs of co-speciation. These endosymbionts have some of the smallest genomes known and are associated with specialized host cells known as bacteriocytes. They are maternally transmitted from mother to offspring, and have an obligatory mutualistic relationship with their host for survival and fertility.