Animal Microbe Interaction

8/8/2019 Animal Microbe Interaction

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I. General: Interactions can beA. mutualistic

microbe provides nutrients

- digestion of substances difficult for animal to degrade

- fixed carbon

- vitamins, cofactorsanimal provides habitat

B. commensal

animal provides habitat

C. predatory

animals preying on microbes - grazing, filter feeding

microbes preying on animals - disease (parasitism),

true predation

Animal-Microbe Interactions


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II. Animal consumption of microorganisms

A. Grazing

1. scrape film of microorganisms (may be

decomposers, may be autotrophs, especially

cyanobacteria) off of surfaces

e.g., snails, urchins

2. consumption of microbes on decomposing feces

- incomplete digestion, especially of cellulose

- microbial breakdown of these undigested compounds

continues after excretion

- reingestion allows more efficient use of food- microbes also provide some vitamins

coprophagy (soil microarthropods, rodents (rabbits), snails)


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3. consumption of microbes on decomposing detritus

microbes convert cellulose and other refractory

compounds into microbial biomass

also immobilize N in the process higher

quality food source (from cellulose, low N:C, to microbialprotein, high N:C)

undigestible detritus is not consumed, microbes recolonize

e.g., earthworms, many aquatic invertebrates (snails, midges)


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Daphnia eats Sphaerocystis, but most of

the Sphaerocystis cells actually survive

passage through the gut ofDaphia

other algae, such as Chlamydomonas,

dont survive and are digested and

assimilated

when in theDaphnia gut, Sphaerocystis

actually absorbs nutrients (such as

phosphorus) from the remains of otheralgae

Thus, grazing actually enhances the

growth ofSphaerocystis in the

community; without Daphnia,

cyanobacteria outcompete Sphaerocystis

4. Effects on communities: grazing by invertebrates can affect

microbial community structure


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5. Grazing, Pollution, and

Evolution

c. They hatched the

eggs and tested their

abilities to eat the toxic

cyanobacteria.

Daphnia swimming amid

toxic cyanobacteria in Lake

Constance

b. Nelson Hairston et al.

collectedDaphnia eggs

in a state of diapause

from the sediments, layer

by layer

a. P pollution over the past30 years has caused a

proliferation of toxic

cyanobacteria in Lake

Constance


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d.Daphnia with 1960s genes were unable to eat the cyanobacteria,

while modern Daphnia were

e. The crustaceans adapted to the less nutritious diet, which not only

ensured their survival, but has also served as a natural control for the

cyanobacteria in the lake.

f. DNA tests further showed that Daphnia evolved from a species thatcould not cope with the toxic bacteria to a species that could.

"It appears that ecological events that we think of as occurring

relatively quickly such as nutrient enrichment of a lake can beinfluenced by the rapid evolution of the animals that are affected...

Strong natural selection can lead to rapid changes in organisms,

which can, in turn, influence ecosystem processes" Nelson Hairston.


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B. Filter Feeding

aquatic animals, sessile benthic invertebrates: sponges, barnacles,polychaete worms, bivalves, etc.

constant flow of water through organism constant supply of

microbes suspended in the water column

microorganisms filtered through gills, tentacles, mucous nets

microbes are autotrophs, heterotrophs, detritus

sea squirts (tunicates, ascidians) and bivalves can capture particles

as small as viruses


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tunicates, so named because the outer layer of the body wall is a

tough "tunic", made of a substance that is almost identical tocellulose

animal consists of a double sac with two siphons: Sea water is

pumped slowly (by cilia) through one siphon, sieved through the

inner sac for plankton and organic detritus, and the filtered seawateris pumped out again through the second siphon, the atrium.

Ascidian Tunicates are called sea squirts because when taken out of

the water they squirt the water inside their body with force throughthe atrium


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Clavelina, a group of transparent sea squirts


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Ciona, with two siphons


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cellulose monomer animal biomass

III. Cellulose digestion key process in animal/microbe mutualisms

cellulose

most abundant carbohydrate in the biosphere chain of glucose molecules linked together

most animals cant degrade it

rely on cellulolytic microorganisms

microbial biomass

degradation products

1. coprophagous and detritivorous animals (above)

2. animals that cultivate microbes externally

3. intestinal symbionts


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IV. Cultivation of Microorganisms (External), plant-eating insects:

A. leaf-cutting ants

mutualism ants excavate cavity in soil

bring leaves to fungus

inoculate leaves w/fungus

fungus grows by decomposing cellulose

ants eat fungus

cellulose --> fungal biomass --> ant biomassalso, when ants eat fungi, the acquire cellulase,

so they are able to continue degrading cellulose in their guts, using

enzyme produced by the fungus

obligate mutualism

fungal garden breaks down without ants

ants protect fungus from competitors

fungus requires ants for dispersal

ants require fungus for food


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Apterostigma

garden


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Worker ant carrying

a piece of fungus


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Atta basidiomycete (many areLepiota) relationship

fungus is deficient in proteases (enzymes that degrade protein)thus, poor competitor w/other fungi

Atta creates high-protease micro-environment

macerates leaves, mixing w/saliva (high in proteases)

adds fecal matter (high in proteases)

then inoculates w/fungal mycelia

thus, relationship maintained by complementary enzyme systems

regionally significant: introduce large amounts of organic

matter to soil


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B. Ambrosia beetles and wood-degrading fungi


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beetles carry fungus in mycetangia

(specialized mouth or leg pouch for

carrying fungi)

as beetles burrow into wood, fungal sporesare dislodged and inoculated (along with

nutrients required by the fungus)

beetles maintain appropriate moisture

conditions in the tunnel by opening and

closing passageways

beetles produce selective antibiotics,

keeping away other microbes

fungus digests cellulose (which beetle isunable to do), produces vitamins and

growth factors

beetle consumes fungus (high in protein);

often, fungus is the sole food source on

which the beetle is capable of surviving


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C. Many others: bark-feeding beetles, ship timber worms,

wood wasps, gall midges

gall midges: larvae and fungal spores deposited into leaves

fungus grows parasitically on plant

larvae eat fungus

D. Termites: external and internal cultivation of microbial

mutualists

cultivate fungi in wood degradationingest fungi to obtain cellulase

also fungal gardens


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V. Intestinal Symbionts

extremely complex gut microflora present in most

animals

monogastric (one gastric chamber)

potential benefits to host:

1) growth factors synthesis

demonstrated importance of growth factor synthesis e.g., vitamin K (deficiency in

germfree animals)

2) pathogen barrier

pathogen

host

mutualist -


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B. Ruminants who are they and why do we care?

deer, moose, antelope, giraffe, caribou, cow, sheep, goat

Ruminants are earths dominant herbivores, due in part to the

evolution within this group of a mechanism utilizing

microorganisms to digest plant components not susceptible to

attack by ruminant enzymes. (Hungate 1975)

Thus, we care for two reasons:

i. Ruminants are earths dominant herbivores in natural ecosystems

ii. Human food economy depends on ruminants


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C. Ruminant digestion diet is high in cellulose, but ruminants

cannot produce cellulase

i. Food is first chewed, then enters the rumen

ii. The rumen is a specialized chamber for microbial fermentation,

containing many bacteria and protozoa

a. rumen environment is quite uniform - anaerobic, high T (30-40

degrees C), neutral pH (5.5-7), constant substrate supply

b. in the rumen, cellulolytic bacteria and protozoa hydrolyze

cellulose to produce cellobiose and glucose


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c. these sugars are then fermented, producing volatile fatty acids

(acetic, propionic, and butyric) and CO2 and CH4

iii. food passes from the rumen into the reticulum, where it is

formed into small portions called cuds

iv. cuds are regurgitated into the mouth where they are chewed

again rumination

v. these solids are now finely divided and very well mixed with

saliva; they are swallowed again, but this time the material enters

the abomasum, an organ more like a true stomach, where truedigestion begins and continues into the small and large intestine


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Diagram of the rumen and gastrointestinal system

of a cow, showing the route of passage of food.


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D. overall fermentation reaction:

cellulose --> acetate, propionate, butyrate, CO2, CH4, H2O

three main products that benefit the animal

i) Volatile fatty acids: acetate, propionate, butyrate

these pass through the rumen wall and are absorbed

propionate used for carbohydrate biosynthesis

acetate, butyrate used for energy

ii) microbial cells contributes protein to ruminants diet

probably the main source of protein

many rumen bacteria can use urea as a sole N source; often part of

cattle feed to promote protein synthesis (cheap meat)

iii) Heat important to the ruminants thermoregulation


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Biochemical reactions in the rumen

end products shown in red (bold)


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E. rumen microflora

i. bacteria:

bacterial populations: 109 to 1011/mL very high

highly specialized bacterial community

all are obligate anaerobes

specific groups specialize in the degradation of cellulose, starch,

hemicellulose, sugar, fatty acids, proteins, fats

some autotrophically produce methane, acetate

many different bacterial genera


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Bacteriodes succinogenes, and Ruminococcus albus

globally among the most important

cellulolytic rumen bacteria

Methanobacterium ruminantium

many other methanogens

composition varies

among different ruminants

among different parts of the world

when diet changes


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ii. protozoa

primarily ciliatesobligate anaerobes

105 to 106 / mL

some degrade cellulose, starch, carbohydrates

(but compared to bacteria, not quantitatively as

important)others are predators

ruminant digests protozoa thus, some protein

contribution to ruminants diet

probably easier for ruminant to digest than

bacteria


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4. Dynamics of rumen ecosystemSudden switch from dried forage (high cellulose) to diet high in glucose or

grain (lower cellulose)

- death within 18 hours

- Streptococcus bovis explosive growth (dividing time of 20

minutes) goes from 107 to 1010 cells/mL

- lactic acid produces lots of lactic acid, which cant go through

rumen wall

- not enough lactic acid degrading bacteria to convert lactate to

VFAs

- pH drops

- tissues destroyed

Gradual diet switch to high protein diet

protozoan predators keep pace with S. bovis

lactic acid degraders also keep pace

possible to maintain balance w/o killing ruminant


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VI. Microbial Predators

Cytophaga

bacterium that eats other bacteria

Many protist grazers amoebae, cilliates, flagellates

Nematode- and Rotifer-trapping fungi


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- fungi that actually prey on nematodes and rotifers- fungi produce traps

adhesive hyphae

constrictive rings

- when nematode swims through ring, ring contracts

immediately by osmotic expansion, trapping thenematode

- hyphae then penetrate inside nematode, degrading it

enzymatically from the inside out (spider)

- trap construction induced by presence of nematodes


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Fungi with adhesive hyphae

Photo by B. A. Jaffee


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Adhesive network

hoto by B. A. Jaffee


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Constricting ring

Photo by B. A. Jaffee


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Electron micrograph of business end of the Haptoglossa Gun Cell. Photograph

by Jane Robb, University of Guelph.

harpoon-shaped projectile


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Epulopiscium fischelsoni

500Qm long, >100x longer than most bacteria

Originally thought to be a protist

Surface:volume problem, solved by membrane invaginations (The large size ofEpulopisciumbaffles people because it seems tobreak the known rules of diffusion limitation and size. However, Kochcalculated with known equations dealing with diffusion limitation andcell size and found that theoretically (according to our known model),the cells could reach a 410 micrometer diameter before diffusionlimitation if an extremely high substrate concentration occured (he

used 0.1% glucose as the substrate concentration) (Shulz andJorgensen 2001). Still, the actual substrate concentration the gut ofsurgeonfish is not known. )


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Even though Epulopiscium is not a Protista, theycontain an unusual cortex which seems to be madeof vesicles, capsules, and tubules, all of which arestructures generally found in protists rather thanbacteria. Some suggest that the vesicles play a partin excreting waste products - this, as well as anintracellular system of transport organelles, might

be what allows Epulopiscium to overcome theconstraints of diffusion limitation with a large cellsize (Shulz and Jorgensen 2001).


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Maturing daughter cells within the E.

fishelsoniparent cell.

A) The daughter cell is ~ 390 by 45micrometers in size and lacks caps -

decondensed DNA is dispersed evenly

below the cell wall.

B) The daughter cell is ~ 350 by 45

micrometers and has two caps.

C) The daughter cell is ~ 350 by 45

micrometers and has a single cap.

D) The daughter cell is ~ 360 by 45

micrometers and has two caps and almost

completely separated DNA.

E) The daughter cell is ~360 by 45micrometers with two caps and

completely separated DNA.


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Thiomargarista namibiensis cangrow to as large as 3/4 of a

millimeter across, which

means it is visible to the

naked eye as a speck

Epulopiscium fischelsoni is large, but not the largest


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Epulopiscium fishelsoni cell that is 237 micrometers long.

The arrows point to two apical nucleoids. From Bresleret al.


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W

hy so big? Some think that the large size might

correlate with its unique method of

reproduction or give it a selective advantageagainst protozoan predation.


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Diurnal Cycle

In the mornings, E.fishelsoni cells (isolated from a surgeonfish gut,not a culture) were found to contain compact, spherical nucleoids atthe apices of the cells which elongated during the day. Throughout theday, the average length of the cells increased witht he nucleoids

making up a large percentage of the parent cell volume. In the lateafternoons and evenings, these nucleoids reached a maximum ofapproximately 50 - 75% of the length of the parent cells. During thenight, over 70% of the E.fishelsoni cells found in the gut containedtwo nucleoids; the rest of the cells were smaller and lacked incipientdaughter cells. These smaller cells, which were almost always foundonly in early morning samples, were assumed to be the released

daughter cells; the parent cells are destroyed in the process of releasingdaughter cells.


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During the day when the nucleoids are elongating and the bacteria arereaching their full size, the surgeonfish would be at its most activefeeding frequently and filling its gut with algal food materials. Inaddition, the metabolism of the E.fishelsoni at this time suppress the

pH of the gut fluids.D

uring the night when the fish would be inactivein reef shelters, the modal cell size declines and the bacteria does notsuppress the pH (Bresleret. al1998).

It is not known if the abnormally large size ofEpulopiscium fishelsonihas anything to do with its unique reproduction in which one or twodaughter cells form inside of the parent cell.Metabacterium polysporais phylogenetically related to E.fishelsoni and is thought by some to

point towards the evolution of the special reproductive system ofEpulopiscium.M.polyspora live in the intestines of rodants, grow toan unusual size (not as large as Epulopiscium, but unusual nontheless),and reproduce by forming two or more refractile endospores per cell(Shulz and Jorgensen 2001).

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Animal Microbe Interaction