Chapter 22b

Question 1

Only microbes have genes for glycoside hydrolases and polysaccharide lyases that can

Answer 1

degrade cellulose, hemicellulose, and other insoluble polysaccharides

Question 2

Cellulose is the mos

Answer 2

abundant component of plant fibers

Question 3

Two digestive plans

Answer 3

Foregut fermentation –Hindgut fermentation–

Question 4

Rumen

Answer 4

pecial digestive organ in some herbivorous mammals (cows, sheep, elk)

Question 5

Site of cellulose digestion

Answer 5

anaerobic microbes-rumen

Question 6

Biochemical reactions in the rumen

Answer 6

1010–1011 microbes/g of rumen
•Cellulolytic microbes that hydrolyze cellulose to free glucose that is then fermented, producing volatile fatty acids (VFAs) and CH4 and CO2

Question 7

Rumen microbes

Answer 7

Synthesize VFAs • Directly digested and serve as protein

Question 8

Anaerobic microbes

Answer 8

–Bacteria –Protists –Fungi –Archaea

Question 9

Rumen microbes continued

Answer 9

• Cellulose decomposers • Starch decomposers • Lactate decomposers • Succinate decomposer • Pectin decomposer • Methanogens

Question 10

All sites on a human that contains microorganisms are part of the

Answer 10

microbiome

Question 11

Human Microbiome Project

Answer 11

Humans are monogastric and omnivorous
•1014 cells present in microbiome (= 10× more
bacterial cells than human cells)

Question 12

The Human Gut Microbial Community

Answer 12

Microbes in gut affect early development, health, and predisposition to disease
•High variability in gut communities between
different individuals

Question 13

Colonization of gut begins at birth-responsible for “maturing” of gastrointestinal tract

Answer 13

Triggering expression of human genes responsible

for nutrient uptake and metabolism –Recognition of gut microflora as nonforeign –Development of mucosal barrier

Question 14

Human gut microorganisms produce

Answer 14

Enzymes –Amino acids –Vitamins

•Firmicutes (64%) •Bacteroides (23%) •Proteobacteria (8%) •Actinobacteria (3%)

Question 15

Human gut microorganisms may play a role in

Answer 15

obesity

Question 16

Mouth and skin are also heavily colonized by microorganisms

•Mouth:

Answer 16

At least 750 species of aerobic and anaerobic

bacteria –Methanogenic Archaea and yeast

Question 17

Mouth and skin are also heavily colonized by microorganisms: skin:

Answer 17

19 bacterial phyla (over 200 genera)
•Corynebacterium (moist sites) •Propionibacterium (oily sites) •Staphylococcus (oily sites)
–Fungi (mainly yeast)

Question 18

Heritable Symbionts of Insects

Answer 18

•Microbial symbionts can be acquired from :
–Environmental reservoir (horizontal transmission) –Parent (vertical or heritable transmission) –Heritable symbionts of insects are obligate (lack a
free-living replicative stage)

Question 19

Primary

Answer 19

Primary symbionts—required for host reproduction
–Restricted to bacteriome, bacterial cells found in bacteriocytes
•Ex: Buchnera supplies amino acids to aphids

Question 20

Secondary

Answer 20

Not required for reproduction –Not always present in every individual –Can invade different cells and live extracellularly –Must provide a benefit
•Nutritional •Protection from environment •Protection from pathogens

Question 21

Some insects exploit the metabolic potential of the symbiont

•Primary symbionts exhibit extreme gene reduction

Answer 21

Genome of insect symbiont ~160 to 800 kbp –Genome of related free-living bacteria ~2 to 8 Mbp –Retain only genes needed for host fitness
•Lose catabolic genes •Pathogens normally lose anabolic genes

Question 22

Termites

Answer 22

Decompose cellulose and hemicellulose

Question 23

Termite gut consists of foregut, midgut, and hindgut

Answer 23

Posterior alimentary tract of higher termites
•Diverse community of anaerobes including cellulolytic
anaerobes
–Lower termites
•Anaerobic bacteria and cellulolytic protists

Question 24

Aquatic Invertebrates as Microbial Habitats: Hawaiian Bobtail Squid

Answer 24

Aliivibrio fischeri and the Hawaiian bobtail squid
•A. fischeri bioluminesce in light organ
•camouflages the squid from predators

Question 25

Aquatic Invertebrates as Microbial Habitats: Hawaiian Bobtail Squid continued

Answer 25

Highly specific •Benefits both partners •Horizontal transmission of
bacterial cells—colonization shortly after juvenile squid hatch
•Bioluminescence is controlled by quorum sensing
•A. fischeri is supplied with nutrients by the squid

Question 26

Marine Invertebrates at Hydrothermal Vents and Gas Seeps

Answer 26

Primary producers in hydrothermal vents are chemolithotrophic microbes
•Diverse invertebrate communities develop near hydrothermal vents, including large tube worms, clams, mussels

Question 27

Chemolithotrophic prokaryotes that utilize reduced

Answer 27

inorganic materials emitting from the vents form endosymbiotic relationships with vent invertebrates

Question 28

Vent tube worms

Answer 28

Trophosome contains symbionts –Hemoglobin binds H2S and O2 –CO2 in blood

Question 29

Leeches

Answer 29

Leeches are parasitic annelids (segmented worms)
•Feed on vertebrate blood and secrete anticoagulants and vasodilators
•Crop has Aeromonas and a Rikenella-like bacterium •Intestinum has complex community
•Bladder—Ochrobactrum

Question 30

Reef-building corals

Answer 30

Coral skeleton very efficient light-gathering structure

•Phototrophic symbionts include cyanobacterium, rhodophytes, chlorophytes, dinoflagellates, and diatoms

Question 31

Reef-Building Corals

Answer 31

Most ecologically significant between stony coral and the dinoflagellate Symbiodinium
•Reef-building corals reproduce sexually by releasing gametes into the seawater
•Algal symbionts are typically found in the egg
•Developing coral can also ingest dinoflagellates
•Cnidarians receive fixed carbon
•Dinoflagellate receives inorganic nutrients

Question 32

Reef-Building Corals: Coral bleaching

Answer 32

• Loss of color caused by lysis of symbiont

* High temperature and high light impair the photosynthetic apparatus of dinoflagellate