I' General: Interactions can be

1
Animal-Microbe Interactions
I. General Interactions can be A.
mutualistic  microbe provides nutrients -
digestion of substances difficult for animal to
degrade - fixed carbon - vitamins,
cofactors animal provides habitat B. commensal
animal provides habitat C. predatory animals
preying on microbes - grazing, filter
feeding   microbes preying on animals - disease
(parasitism), true predation
2
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)
3
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 NC, to microbial protein,
high NC)   undigestible detritus is not
consumed, microbes recolonize e.g., earthworms,
many aquatic invertebrates (snails, midges)
4
4. Effects on communities grazing by
invertebrates can affect microbial community
structure
  Daphnia eats Sphaerocystis, but most of the
Sphaerocystis cells actually survive passage
through the gut of Daphia other algae, such as
Chlamydomonas, dont survive and are digested and
assimilated when in the Daphnia gut,
Sphaerocystis actually absorbs nutrients (such as
phosphorus) from the remains of other algae Thus,
grazing actually enhances the growth of
Sphaerocystis in the community without Daphnia,
cyanobacteria outcompete Sphaerocystis
5
5. Grazing, Pollution, and Evolution
a. P pollution over the past 30 years has caused
a proliferation of toxic cyanobacteria in Lake
Constance
b. Nelson Hairston et al. collected Daphnia eggs
in a state of diapause from the sediments, layer
by layer
c. They hatched the eggs and tested their
abilities to eat the toxic cyanobacteria.
Daphnia swimming amid toxic cyanobacteria in Lake
Constance  
6
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 that could 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 be influenced
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.  
7
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
8
tunicates, so named because the outer layer of
the body wall is a tough "tunic", made of a
substance that is almost identical to cellulose
  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 seawater is 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 through the atrium
9
Clavelina, a group of transparent sea squirts
10
Ciona, with two siphons
11
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
cellulose monomer animal biomass
degradation products
microbial biomass
1. coprophagous and detritivorous animals
(above)   2. animals that cultivate microbes
externally   3. intestinal symbionts
12
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 --gt fungal
biomass --gt ant biomass also, 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
13
(No Transcript)
14
 
Apterostigma garden
15
Worker ant carryinga piece of fungus
16
Atta basidiomycete (many are Lepiota)
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

17
B. Ambrosia beetles and wood-degrading fungi  
18
beetles carry fungus in mycetangia (specialized
mouth or leg pouch for carrying fungi) as
beetles burrow into wood, fungal spores are
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
is unable to do), produces vitamins and growth
factorsbeetle consumes fungus (high in
protein) often, fungus is the sole food source
on which the beetle is capable of surviving
19
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
degradation ingest fungi to obtain
cellulase also fungal gardens
20
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
21
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
22
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
23
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 true digestion
begins and continues into the small and large
intestine
24
Diagram of the rumen and gastrointestinal system
of a cow, showing the route of passage of food.
25
D. overall fermentation reaction cellulose
--gt 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
26
Biochemical reactions in the rumen end products
shown in red (bold)
27
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
28
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
29
ii. protozoa primarily ciliates obligate
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
30
4. Dynamics of rumen ecosystem Sudden 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
31
VI. Microbial Predators   Cytophaga bacterium
that eats other bacteria   Many protist grazers
amoebae, cilliates, flagellates   Nematode- and
Rotifer-trapping fungi
32
- 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 the
nematode - hyphae then penetrate inside
nematode, degrading it enzymatically from the
inside out (spider) - trap construction induced
by presence of nematodes
33
Photo by B. A. Jaffee
Fungi with adhesive hyphae
34
Photo by B. A. Jaffee
35
Photo by B. A. Jaffee
36
(No Transcript)
37

• Rotifer killers, Haptoglossa mirabilis
• infects rotifer host by means of a gun-shaped
  attack cell
• the anterior end of the cell is elongated to form
  a barrel
• the wall at the mouth is invaginated deep into
  the cell to form a bore
• walled chamber at the base of the bore houses a
  complex, missile-like attack apparatus
• projectile is fired from the gun cell at high
  speed to accomplish initial penetration of the
  host
• spore then develops into fungus, killing the
  rotifer

38
(No Transcript)
39
(No Transcript)
40
(No Transcript)
41

• Epulopiscium fischelsoni
• 500 mm long, gt100x longer than most bacteria
• Originally thought to be a protist
• Surfacevolume problem, solved by membrane
  invaginations
• (The large size of Epulopiscium baffles people
  because it seems to break the known rules of
  diffusion limitation and size. However, Koch
  calculated with known equations dealing with
  diffusion limitation and cell size and found that
  theoretically (according to our known model), the
  cells could reach a 410 micrometer diameter
  before diffusion limitation if an extremely high
  substrate concentration occured (he used 0.1
  glucose as the substrate concentration) (Shulz
  and Jorgensen 2001). Still, the actual substrate
  concentration the gut of surgeonfish is not
  known. )

42

• Even though Epulopiscium is not a Protista, they
  contain an unusual cortex which seems to be made
  of vesicles, capsules, and tubules, all of which
  are structures generally found in protists rather
  than bacteria. Some suggest that the vesicles
  play a part in excreting waste products - this,
  as well as an intracellular system of transport
  organelles, might be what allows Epulopiscium to
  overcome the constraints of diffusion limitation
  with a large cell size (Shulz and Jorgensen
  2001).

43
Maturing daughter cells within the E. fishelsoni
parent cell. A) The daughter cell is 390 by 45
micrometers 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 45 micrometers with
two caps and completely separated DNA.
44
Epulopiscium fischelsoni is large, but not the
largest
45
(No Transcript)
46
Epulopiscium fishelsoni cell that is 237
micrometers long. The arrows point to two apical
nucleoids. From Bresler et al.
47
Why so big?

• Some think that the large size might correlate
  with its unique method of reproduction or give it
  a selective advantage against protozoan
  predation.

48
(No Transcript)
49
Diurnal Cycle

• In the mornings, E. fishelsoni cells (isolated
  from a surgeonfish gut, not a culture) were found
  to contain compact, spherical nucleoids at the
  apices of the cells which elongated during the
  day. Throughout the day, the average length of
  the cells increased witht he nucleoids making up
  a large percentage of the parent cell volume. In
  the late afternoons and evenings, these nucleoids
  reached a maximum of approximately 50 - 75 of
  the length of the parent cells. During the night,
  over 70 of the E. fishelsoni cells found in the
  gut contained two nucleoids the rest of the
  cells were smaller and lacked incipient daughter
  cells. These smaller cells, which were almost
  always found only in early morning samples, were
  assumed to be the released daughter cells the
  parent cells are destroyed in the process of
  releasing daughter cells.

50

• During the day when the nucleoids are elongating
  and the bacteria are reaching their full size,
  the surgeonfish would be at its most active
  feeding frequently and filling its gut with algal
  food materials. In addition, the metabolism of
  the E. fishelsoni at this time suppress the pH of
  the gut fluids. During the night when the fish
  would be inactive in reef shelters, the modal
  cell size declines and the bacteria does not
  suppress the pH (Bresler et. al 1998).
• It is not known if the abnormally large size of
  Epulopiscium fishelsoni has anything to do with
  its unique reproduction in which one or two
  daughter cells form inside of the parent cell.
  Metabacterium polyspora is phylogenetically
  related to E. fishelsoni and is thought by some
  to point towards the evolution of the special
  reproductive system of Epulopiscium. M. polyspora
  live in the intestines of rodants, grow to an
  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).