Microbial Symbioses with Plants and Animals

symbiosis

means living together

commensal relationship

have no effect on host

parasitic

causes disease on host

mutalistic (symbiotic)

both microbe and host benefit

most are ancient and have involved co-evolution

microbial consortium

two or more nacterial or microbial groups living symbiotically

consortia

microbial mutualisms

Chlorochromatium aggregatum

green sulfur bacteria (epibionts) and colorless flagellated rod-shaped bacterium

green bacteria will cover colorless bacteria - these bacteria can make themselves rise or fall in the lake

epibionts = obligate anaerobic phototrophs

make up 70% of the bacterial biomass in stratified sulfidic lakes

Use H2S for CO2 fixation

Once assembled, consortia repositions itself for most favorable photosynthesis and sulfide concentration

Gas vesicles help this!

microbial consortia

very successful and almost obligate relationship

gets to point where these bacteria need each other

legume root nodule symbiosis

legumes = plants with seeds in pods

nitrogen fixing bacteria and legumes is one of the most important symbioses known

rhizobia are the best known nitrogen fixing bacteria engaging in these symbioses

Alphaproteobacteria or Betaproteobacteria that can grow freely in soil or infect leguminous plants

root nodules

infection of legumes roots by nitrogen-fixing bacteria leads to the formation of root nodules

root nodules fix nitrogen

leads to increases in combined nitrogen in soil

nodulation

how a root nodule is created

there must be a receptor in root cell

root nodule formation steps

recognition and attachment of bacterium to root hairs

excretion of nod factors by the bacterium

bacterial invasion of the root hair

travel to the main root via the infection thread

formation of bacteroid state within plant cells

continued plant and bacterial division, forming the mature root nodule

the symbiosome

after infection, rhizobia rapidly divide in the root nodule

these bacteria change shape and are called bacteriods that form a symbiosome within the nodule

The legume–bacteria symbiosis is characterized by

oxygen sequestration, several metabolic reactions, and nutrient exchange

bacteriods are dependent on plant to provide what

pyruvate (fuel) for nitrogen fixation

how can microbial symbionts be acquired

vertical or horizontal gene transfer

aka environmental reservoir (horizontal transmission)

and parent (vertical or heritable transmission)

primary symbionts

required for the host to reproduce

restricted to bacteriome

bacterial cells are found in bacteriomes

vertically transmitted

symbiont

organism living in symbiosis with another organism

secondary symbionts

not required for reproduction

not always present in every individual

can invade different cells and live extracellularly

must provide a benefit

• nutritional

• protection

so basically like a fun addition that can be aqquired in life doesnt matter when

wolbachia

gram negative bacterium that live in mosquitos

vertically transferred (thru eggs laid)

sperm of wolbachia infected males can sterilize uninfected females

stop spread of dengue

how does wolbachia gets passed on

IT STERALIZES VECTOR

if a mom has it but dad doesnt - all eggs will have it

if dad has it but mom doesnt - no eggs will hatch

if both parents have it, all eggs will have it

Species involved in forming symbiosomes in corals

Phototrophic symbionts include cyanobacteria, rhodophytes, chlorophytes, dinoflagellates (symbiodinium is a type of dinoflagellates), and diatoms

symbiosomes

the coral harbors the dinoflagellates (Microbial algae) inside the special vesicles called symbiosomes

coral are really good at what

coral skeleton are very efficient light gathering structures

dinoflagellates benefit how from coral

the coral improves the light-gathering capacity of the dinoflagellates

how does coral benefit from dinoflagellates

the photosynthesis of the dinoflagellates provides organic nutrients to the coral

how are dinoflagellates passed

vertical transmission

corals reproduce sexually by releasing gametes into the seawater

or coral can ingest bacterium from environment

coral bleaching

high temperatures and high light impair the photosynthetic apparatus of dinoflagellate

lysis of dinoflagellate leads to loss of color

nearly half the great barriar reef has experienced bleaching in the past few years

aka this bacteria and color have an obilgate relationship - w/o the bacteria the coral dies

dysbiosis

imbalance in the microbial communities

scleractinia

fancy word for coral

how coral bleaching happens

HUMANS UNLEASH CO2 AND BRING ABOUT MORE MICROBES

CO2 WARMS AND ACIDIFIES THE OCEANS

CORALS EXPEL ALGAE INSIDE THEIR BODIES WHICH PROVIDE THEM WITH NUTRIENTS

CORALS BECOME WEAK AND GHOSTLY AND IMMUNO COMPROMISED SO THEY DIE OF MALNUTRITION AND INFECTION

cellulose

most abundant organic compound on earth

not all animals can digest it so a selective advantage is given to those who digest cellulose

evolved traits that allow for digestion of cellulose

large anoxic fermentation chamber

extended retention time for proper digestion

proper microbiota

foregut fermentation

fermentation chamber precedes the small intestine

hindgut fermentation

uses cecum and/or large intestine

ruminants

herbivorous mammals (cows sheeps goats) = foregut fermenters

what do ruminants possess

the rumen (special digestive organ)

microbes in rumen allow for digestion of cellulose and other polysaccharides

microbes are killed by the acidity of the stomach and become protein source for the animal

rumen is well studied bc of implanted sampling port

rumens = ?

large anoxic vessels

ruminant digestion

food enters - goes to reticulum

food particles flow between reticulum and rumen

small food particles flow thru to omasum and then to abomasum

larger food particles get regurgitated and digested with saliva in the rumen prior to continuing

food particles that are not digested can stay for up to 1 day

how many microbes per gram of rumen constituents

10^10 to 10^11

fermentation =

microbes hydrolyze cellulose to free glucose that is then fermented producing volatile fatty acids

Fatty acids pass through the rumen wall into the bloodstream and are utilized by the animal as its main energy source

What are examples of fermentation products of anaerobic bacteria in cow rumen

fatty acids

VFAs - e.g., acetic, propionic, butyric and CH4 and CO2

rumen microbes functions

synthesize amino acids and vitamins for the animal host

microbes = source of protein to the host when directly digested

how many bacterial species in rumen plus what is the dominate bacteria type

300 to 400 bacterial species

anaerobic bacteria dominate in the rumen

what is the type of nucleic acid sequenced to differentiate microbiota species

16S rRNA gene