Lecture 09 Vertebrate Gut Symbioses

The symbionts of vertebrate guts are typically …

heterotrophic microbes

most symbioses are ________, but important members are ___ _________ at least

transient, semi perminent

Most vertebrate gut symbioses are ____-cellular

extra

Most vertebrate gut symbioses are obligate/ facultative and unculturable/culturabe

obligate, culturable

what are typical gut symbiosis features of the host

provides habitat and steady stream of unprocessed food ( host as habitat )

typical gut symbiosis features of the symbiont community

possesses pathways to metabolize food (source of metabolic innovation)

what hosts contain cellulose-degrading symbionts?

herbivorous vertebrates, wood-eating insects, shipworms (a marine bivalve mollusc)

Why would animals have celluose-degrading symbionts?

hosts lack enzymes to degrade complex polysaccharides

define syntrophy

metabolic interdependece

What is the metabolic premise ?

1. symbionts hydrolyze polysaccharides into simple sugars

2. other symbionts ferment sugars anaerobically into volatile fatty acids

3. Host absorbs the volatile fatty acids, using them as fuel for aerobic respiration

Symbionts contribute to hosts _______ budget by ?

nitrogen; recycling host N wastes or fixing N into proteins and amino acids some sy

some symbionts produce _________ to help maintain the anaerobic environment of the guy

methane

foregut fermenters include:

ruminant, colobine monkeys, sloth, macropod marsuipials, hoatzin.

hindgut fermenters include:

Cecal fermenters- rabbits and hares, some rodents, grouse, some reptiles

hindgut fermenters- equids, some rodents, humans, some reptiles

foregut symbioses evolved _____________ in just ___ mammals and one strange bird

independently, 4

hindgut symbioses have a wide/ narrow taxonomic range

wide

The hindgut has a _______ pH and is largely enzymatic/nonenzymatic. Why?

neutral, nonenzymatic; because it functions in absorption of water/ ions, not digestion of material

What are the 4 orders of mammalian foregut symbioses?

marsupiala - kangaroos

primatia - colobus monkey

edentata - sloths

artiodactyla - hippos, camels, ruminants

What is the bird that has a foregut symbiosis?

Opisthocomos hoazin

• diet is 80% leaves

What are the common characteristics of foregut symbioses?

• in herbivores with diet rich in plant structural polysaccharides

• foregut = enlarged, up to 30% bodyweight

• foregut has multiple chambers

• part of foregut is anaerobic and contains dense bacterial population

• pH close to neutral, maintained by bicarbonate rich saliva

• high concentration of VFAs (main products of anaerobic fermentation of sugars)

ruminants all have _________ symbioses

foregut

the common ancestors of ruminants featured a _______, which was an enlarged foregut for fermentation

rumen

what is indicated in purple and what does it do?

rumen and reticulum- symbionts occur and are active here. This is also the site of some VFA absorption

what is labelled in yellow and what does it do?

omasum- takes up VFAs and bicarbonate

what is labelled in green and what does it do?

abomasum - the true stomach that performs acidic digestion

what is a cow’s chewing cud?

where they repeatedly chew food, swallow, vomit, shew, swallow again

why do cows perform chewing cud?

adds saliva and bicarbonate to food, which breaks down food into smaller particles

what is the pathway order in the cow’s system?

mouth > rumen > repeat > omasum > abomasum

the rumen is largely _________

anaerobic

what are the layers of the rumen?

top- gases

middle- fluid of today’s hay

bottom- fluid of yesterday’s hay

why are there multiple layers in the rumen?

as new material comes in, anaerobic fermentation can continue because low O2 concentrations are maintained with high CO2 and methane concentrations

what is the fluid that food lands in to be digested?

liquor- contains symbionts

small amounts of O2 are removed by __________ anaerobes in the rumen

facultative

in the rumen, facultative means the capacity to…

perform both aerobic and anaerobic respiration

VFAs are absorbed across the ________ ____

rumen wall

gas phase of the rumen is ????

CO2 and methane

what are characteristics of obligate anaerobic eubacteria?

die if O2 present

some degrade complex plant material

some ferment only starch/simple sugars

some specialize in glycerol fermentation

several metabolize and deanimate proteins

methanogens are what type of eubacteria ?

obligate anaerobes

what are characteristics of methanogens

produce methane from H2 and host food

result in net loss of 10% energy intake

• H2 removal from system favors important reactions though

  • methanogenic ectosymbionts scrub H2 off of anaerobic ciliates

What are characteristics of facultative anaerobic bacteria?

can respire if O2 present, but switch to fermentation in its absence

some degrade urea (important for nitrogen cycling)

others degrade material using reactions that require oxygen

keep O2 levels down

Protozoa are mostly _____

ciliates

characteristics of protozoa as gut symbionts?

responsible for 30-60% fermentation

Not essential

obligate anaerobes, many specific to rumen

perform phagocytosis of particles of plant material and break down to simple sugars/ VFAs

• phagocytosis of bacteria as a source of nitrogen

• methanogens associated with their cell surface to remove H2

characteristics of fungi as gut symbionts

produce cellulases

good at breaking down lignin-rich plant cell walls

which microbes are responsible for cellulose degrading ?

eubacteria, ciliates/protozoans, fungi

which microbes are responsible for fermentation?

eubacteria and ciliates/protozoans

which microbes are responsible for nitrogen metabolism ?

eubacteria

which microbes are responsible for methane production?

archaea, eubacteria

What is the carbon budget?

since ruminant diet is almost entirely carbs, symbionts break them down to monosaccharides. They perform glycolysis to form pyruvate, in which the pyruvate synthesizes VFA’s via fermentation. VFAs absorbed and used in metabolism

what is the nitrogen budget?

ruminant diet is nitrogen poor, so the symbiosis conserves or recycles nitrogen. Symbionts break down organic nitrogen proteins to NH4, and use it in their amino acid synthesis that are absent in the food being consumed. There are also urea metabolizers that can produce NH4 for amino acid synthesis. The host digests 30% of symbionts (because it doesn’t absorb nitrogen until the stomach) and derives a mixture of amino acids from them which ludes the essential amino acids it can’t synthesize itself.

how do rumen symbionts transmit?

horizontally; the juvenile gut lacks the digestive symbionts, and it firsts gains ones that help it break down milk. Then, cellulase-degrading bacteria/protists are obtained when a mother licks her calf or from airborne saliva that have the symbionts

What are the animals that are considered hindgut fermenters?

humans/primates

horses/rhinos/tapirs

manatees

rabbits

rodents

koalas/wombats/opossums

birds

iguanas/turtles

hindgut symbioses are similar to foregut symbioses with what exception?

where the digestion/absorption is taking place

a caecum or a colon may be used in hindgut fermentation, both are what kind of environment?

anaerobic

what is coprophagy? why do animals do it?

eating your own poop; since symbionts are found after the stomach, host cannot digest them easily, so the fecal matter is re-ingested and this aids in nutrient cycling. it is also a method of symbiont transmission (horizontally)