Symbiosis Flashcards
What is the Black queen hypothesis?
Organisms loose genes over time and rely on those produced in the community, individual cells depend on each other (symbiosis).
Can become obligate symbionts i.e. they can’t survive without each other.
What are endosymbionts? And what is SET theory?
Some symbionts internal
Coevolution of host and endosymbiont can result in the endosymbiont loosing genes.
SET theory:
Ancestral prokaryote engulfed an aerobic heterotrophic Prokaryote which became the Mitochondria.
What are consortia?
Occur in freshwater
Microbial mutualisms
Consist of photosynthetic cells surrounding a motile cell - The two cell types are unrelated species.
What is Chlorochromatium aggregatum
(consortia)?
Green sulfur bacteria and a flagellated rod-shaped bacterium
Found in stratified sulfidic lakes.
Motile cell allows them to move up and down the water column. Finding the optimum light, oxygen and sulphur levels at various times of day.
Green sulfur bacteria make up 67% percent of the bacterial biomass in these lakes, and 90% of green sulfur bacteria live in this symbiotic form.
Lichen structure
Algal Layer
Fungal Hyphae - increases surface area
Root-like (fungal) connection to substrate
Lichen symbiosis
Grow on bare rocks, tree trunks, house roofs, and the surfaces of bare soils.
Mutualistic relationship between a fungus and an algae (or cyanobacterium).
Can contain bacterial and archaeal microbiota.
‘Algae’ is photosynthetic and produces organic matter; many are nitrogen-fixing as well.
Fungus provides a structure within which the phototrophic partner can grow protected from erosion and with dissolved inorganic nutrients
What is nitrogen fixing?
Atmospheric nitrogen insoluble to plants
Bacteria tranforms nitrogen to soluble
Nitrate and ammonium
What is Rhizosphere?
The region of soil in the vicinity of
plant roots in which the chemistry and microbiology
is influenced by plants growth respiration, and nutrient exchange.
There are 10-100 times more bacteria around roots.
Up to 20% of sugars created through photosynthesis go to ‘feeding’ microbes.
How to legumes demonstrate symbiosis?
Legumes are the 3rd most abundant group of flowering plants.
Include commercially important crops such as beans, peas, chickpeas, lentils, soybeans, and peanuts.
Root nodules designed for growing bacteria in root systems
Different rhizobia bacteria infect different species of legumes
Nitrogen-fixing bacteria need O2 to generate energy for N2 fixation, but the enzymes that fix nitrogen, the nitrogenases, are inactivated by O2.
In the nodule, free oxygen is bound up by O2-binding protein leghemoglobin that serves as an “oxygen buffer” to protect nitrogenases from free oxygen
What is Mycorrihizal? What are the two types?
Fungi - at least 460 million years ago and might have helped plants colonize land.
Ectomycorrhizae (10%).
Endomycorrhizae (85%)
(Arbuscular mycorrhizae).
> 90% of ALL plants have mycorrhizae.
How do fungi benefit plants? What does the fungi get in return?
Increase surface area.
Increase water absorption.
Release nutrients.
Plants couldn’t have colonised land without fungi.
In return fungi get sugars from plant. Up-to 20% of all sugar generated from photosynthesis is ‘fed’ to soil microbes.
How many insects support symbiotic microbes?
20%
How are insect microbial symbionts acquired?
Environmental reservoir (horizontal transmission).
Parent (vertical or heritable transmission).
Heritable symbionts of insects are obligate (lacking a free-living replicative stage).
What are primary symbionts?
Essential for hosts to reproduce
Primary symbionts have reduced genome – no longer able to live in environment.
Retain only genes needed for host fitness.
What is secondary symbiosis?
Not required for reproduction.
Not always present in every individual.
Can invade different cells and live extracellularly.
Must provide a benefit e.g. nutritional, protection from environment, protection from pathogens
