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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
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.
- Microscopic organisms
- Found in marine sediments and pelagic
zone, freshwater lakes, soils,
- Live in extreme environments – chemically
and temperature.
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 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
Habit – success due to ability
tolerate a wide range of conditions
Marine – littoral and pelagic
Fresh Water
Hot Springs
Terrestrial – soil flora
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
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
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
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
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.
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