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CYANOBACTERIA

General characteristics:

• Prokaryote, hence absence of

organelles.

• Oxygenic Photosynthetic organism;

nitrogen fixing.

• Cell wall Gram negative bacterial.

• Live in association with other

organisms forming microbial mats,

biofilms and benthic communities.

Widespread in freshwater, marine

and terrestrial ecosystems,

•Cyanobacteria Cells small usually < 10μm,

• lacking nucleus, chloroplasts or other membrane

bound organelles, often with heterocysts or akinete

spores.

• Blue-green in colour due to a water soluble accessory

pigment (phycocyanin)

• Growth form as unicells, small clusters, filaments, or large

colonies

• photoautotrophs, aerobic

• Molecular evidence shows them to be the ancestors of

algal chloroplasts

Cyanobacteria

Cyanobacteria

Cyanobacteria

Modern day cyanobacteria include nearly 2000 species

in 150 genera in 5 orders, (Table 1), with varieties of

shapes and sizes. The major groups in the aquatic

environment are the mat forming, the bloom-formers

and the picocyanobacterias. Nutrient-rich eutrophic

lakes suffer the bloom formation due to toxic

cyanobacteria. Cyanobacterial hazards to human

health, has to be understood with, the knowledge of

behaviour in natural ecosystems, and the

environmental conditions which support the growth of

certain species is helpful.

Cyanobacteria

- Microscopic organisms

- Found in marine sediments and pelagic

zone, freshwater lakes, soils,

- Live in extreme environments – chemically

and temperature.

Cyanobacteria

Prokaryotes Eukaryotes

Cyanobacteria

BOTANY

Cyanobacteria

Importance

1) First organisms to have 2 photosystems and to produce organic material and give off O2 as a bi-product.

Very important to the evolution

of the earths’ oxidizing atmosphere .

Cyanobacteria

Importance 2) Many – fix or convert atmospheric nitrogen into

usable forms through Nitrogen Fixation when

other forms are unavailable.

IMPORTANT because atmospheric N2 is

unavailable to most living organisms because

breaking the triple bond is difficult

N N

Cyanobacteria

Cyanobacteria

Cyanobacteria Characteristics

Pigments – chl a, phycobiliproteins

- phycoerythrin

- phycocyanin * Blue-Green Color

- allophycocyanin

Storage – glycogen

Cell Walls – amino acids, sugars

Cyanobacteria

Forms Unicell – with mucilaginous envelope

Colonies –

Filaments – uniserate in a single row

- OR - multiserate – not TRUE branching

when trichomes are > 1 in rows

Cyanobacteria

Features Trichome – row of cells

Mucilaginous sheath –

layer of mucilage outside of the cell wall.

} Filament

Cyanobacteria

Features Mucilaginous Sheath –

Function – protects cells from drying

and involved in gliding.

Sheath is often colored:

Red = acidic

Blue = basic

Yellow/Brown = high salt

Cyanobacteria

Features Heterocyst – thick walled cell, hollow

looking. Larger than vegetative cells.

FUNCTION – provides the anaerobic

environment for N fixation.

H- heterocyst

Cyanobacteria

Anabaena

Heterocyst

Vegetative cells

Cyanobacteria

Cyanobacteria

Habit – success due to ability

tolerate a wide range of conditions

Marine – littoral and pelagic

Fresh Water

Hot Springs

Terrestrial – soil flora

Cyanobacteria

Cyanobacteria

Heterocyst Larger than vegetative cells

Hollow looking

Thick walled – doesn’t allow atmospheric gas to enter.

Photosynthetically inactive

No CO2 fixation or O2 evolution

Formation of heterocysts triggered by [molybdenum] and and low [nitrogen]

Cyanobacteria

Nitrogen

Nitrogen is a limiting nutrient necessary for

the production of amino acids = building

blocks of life.

Cyanobacteria

Nitrogen Fixation

ONLY cyanobacteria and prokaryotic

bacteria can FIX nitrogen.

Of these two only CYANOBACTERIA

evolve OXYGEN during photosynthesis

Important because nitrogenase (enzyme

involved in fixing nitrogen) is INACTIVATED

by O2.

Cyanobacteria

Mechanisms to Separate

Nitrogenase from Oxygen

Heterocyst (spatial)

OR

Fix Nitrogen in the DARK but not LIGHT –

found in non-heterocystic cyanobacteria

(temporal)

Cyanobacteria

AEROBIC

CO2 + H2O ----------- CH2O (sugar) +O2

Electrons for PS1 come from PS2 which evolves oxygen

(splitting of water)

LIGHT

Cyanobacteria

ANAEROBIC

in the presence of sulfer

2H2S + CO2 -------- CH2O +2S + H2O

H2S is the electron donor – so the reaction does not

produce oxygen.

Cyanobacteria

Advantage for Cyanobacteria

Can live in fluctuating environments

of aerobic and anaerobic with light

present.

Cyanobacteria

Cyanotoxins in Cyanobacteria

Neurotoxins – block neuron transmission in muscles

(Anabaena, Oscillatoria)

Hepatotoxins – inhibit protein phosphatase, cause

liver bleeding. Found in drinking water.

(Anabaena, Oscillatoria, Nostoc)

Eg. swimmers itch - Lygnbia

Cyanobacteria

Movement

No flagellae or structures to enhance

movement

A) Excrete mucilage – jet propulsion, gliding

B) Helix – fibers send waves of contraction

Spirulina

Cyanobacteria

Spirulina

• filamentous

• common in lakes with high pH

• major food for flamingo populations

• commercial food source

Cyanobacteria

Anabaena with a heterocyst

- common bloom forming species with nutrient loads

Cyanobacteria

Lyngbia martensiana

Releases chemicals causing dermatitis

Cyanobacteria

Asexual Reproduction

- Hormogonia formation -

- Endospore / Akinete formation -

- Fragmentation –

- Exospore

Cyanobacteria

Asexual Reproduction Hormogonia – short piece of trichome found in

filaments. It detaches from parent filament and glides away

Hormogonia

Cyanobacteria

Oscillatoria with hormogonia

- short pieces of a trichome that become detached

from the parent filament and glide away to form

new filament.

Cyanobacteria

Oscillatoria (filamentous) with hormogonia

Cyanobacteria

Asexual Reproduction Akinete – thick walled resting spore

A - akinete H

Cyanobacteria

Akinete

Cyanobacteria

Asexual Reproduction

Akinete – thick walled resting spore

Function – resistant to unfavorable environmental conditions.

Appear as larger cells in the chain and different than heterocyst. Generally lose buoyancy

A - akinete H

Cyanobacteria

Asexual Reproduction Fragmentation - fragmentation

Cyanobacteria

Oldest Fossils

3.5by old carbonaceous microfossils S.Africa

3.4by old filaments and microbial fossils – W.

Australia

3.4 by old stromatolites – S.Africa, Australia

Cyanobacteria

Stromatolites – Shark Bay, W. Australia

Cyanobacteria and Understanding the Past

Cyanobacteria

Cyanobacteria

Cyanobacteria

The basic features of photosynthesis in cyanobacteria

have been well described.

Cyanobacteria are oxygenic phototrophs possessing two

kinds of reaction centres, PS I and PS II, in their

photosynthetic apparatus.

With the accessory pigments mentioned above, they are

able to use effectively that region of the light spectrum

between the absorption peaks of chlorophyll a and the

carotenoids.

Cyanobacteria

The ability for continuous photo-synthetic growth in the

presence of oxygen, together with having water as their

electron donor for CO2 reduction, enables cyanobacteria to

colonise a wide range of ecological niches. Phycobiliprotein

synthesis is particularly susceptible to environmental

influences, especially light quality. Chromatic adaptation is l

attributable to a change in the ratio between phycocyanin

and phycoerythrin in the phycobilisomes. Thus,

cyanobacteria are able to produce the accessory pigment

needed to absorb light most efficiently in their habitat.

Cyanobacteria

Cyanobacteria

Cyanobacteria

External appearance of some cyanobacteria collected from paddy fields in Sri

Lanka.

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