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Evolutionary history of blue-green algae

Earth is about 4.5 billion year old

Precambrian Eon is from 4.5 to 0.5 billion years ago (bya)

Evidence of O2-producing photosynthesis 3.7 bya

Oldest possible biological structures of blue-green origin,~3.5-2.7 bya => stromatolites

Oldest convincing fossils of individual blue-greens 2.0 bya

O2 is prerequisite for O3 (ozone), which absorbs ultraviolet

light, making possible the invasion of land Familiar plant and animal phyla have existed for only the last

10-15% of the history of the planet.

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Stromatolites

Layered mounds composed mostly of sediment

First biogenic structures known; organisms not preserved, but

structures are obviously of biological origin

Orientation toward light Layer of blue-green algae traps, then overgrows sediment

Became less abundant in fossil record as invertebrate grazers

evolved, but still are formed in a few places

Oldest known stromatolites date to 3.5 billion yrs ago

Stromatolite-like structures in your backyard

fossilized: Petrified Gardens nearSaratoga Springs, NY

living: Green Lake nearSyracuse

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Shark Bay, Australia

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Petrified Sea Gardens

Saratoga Springs, NY

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Life in extreme environments: mats of reddish blue-greens around

hot springs in Yellowstone may represent ancient environment

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Nitrogen fixation

Nitrogen is often a limiting nutrient, most organisms can useonly nitrate or ammonia; nitrogen fixation avoids N limitation.

Nitrogenase (essential enzyme in N2 fixation) is poisoned by O2-photosynthesis inhibits N fixation

Solutions to oxygen problem:

heterocyst: thick-walled vegetative cell that ceases O2generation and carries on N2 fixation

some unicells without heterocysts fix N2 only in the dark

some filaments without heterocysts form bundles of parallel

filaments; shaded central filaments fix N2 Symbiotic relationships promoted by N2 fixations

cycads

Azolla (water fern)

blue-green lichens

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heterocysts

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Autofluorescence ofphotosynthetic pigments: no

pigment in heterocysts, thereforeno photosynthesis, no O

2generation

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Physiological

specialization andintegration in one

filament:

- nitrogen fixation by

heterocyst

- tapering, hair-likefilament has high

surface to volume

ratio for phosphate

uptake

- akinete (restingspore) stores both N

and P

heterocyst - akinete - normal cells - hairheterocyst - akinete - normal cells - hair

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Coralloid roots of cycads house

blue-greens

Symbiotic nitrogenfixation

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Azolla

blue-greens

Floating fern,Azolla, has a pouch on

the underside of each leaf in whichAnabaena grows.

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Azolla in agriculture

In pureNostoc orAnabaena culture, 6-10% of the cells in the

filament are heterocysts, frequency increases under nitrogen

deprivation (no available N compounds in water).

InAzolla leaf, 20-30% of algal cells become heterocysts.

Rates of N2 fixation can be 2 kg of N per hectare per day.

Azolla is used in China on 1.5 million hectare annually.

New community products.

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Problem blue-green

algal blooms

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Cyanotoxins

microcystin (Microcystis): hepatotoxin

acute poisoning can cause death; prolonged non-lethaldoses linked to liver cancer

over 50 died in hemodialysis facility in Brazil from

microcystin poisoning

anatoxin (Anabaena): neurotoxin

mimics acetylcholine but cannot be degraded so musclescontinue to contract, paralysis, suffocation

aphanotoxin [saxitoxin-PS

P] (Aphanizomenon): neurotoxin

blocks sodium ion channels, inhibits nerve impulse

dermatoxins - skin rash from swimming

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The usual suspects:

Annie, Fannie, and

Mike

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Black band disease ofcorals is caused by a

blue-green alga

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Stains on roofs are caused by 'black algae' => blue-green alga

Gleocapsa.

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Stains on polar bears in zoos is caused by blue-greens

living inside broken off hollow hairs.

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Blue-greens in commerce:

food supplements

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Spirulina and commercial aquaculture ponds in Hawaii

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Aphanizomenon harvester in Klamath Lake, Oregon -

harvesting wild populations