Download Cyanobacteria - U of L Class Index

Cyanobacteria
•Cells small usually < 10 m,
•lacking nucleus, chloroplasts or other
membrane bound organelles,
•Contain chlorophyll a and possibly other
Unicellular cyanobacteria
accessory chlorophylls (e.g. chl b), and
carotenoids
Synechococcus, cells 8-10 microns
•often with heterocysts or akinete spores.
•Blue green in colour due to a water soluble
Chroococcus, cells 8- 10 microns
accessory pigment (phycocyanin)
•Growth form as unicells, small clusters,
filaments, or large colonies
•photoautotrophs, aerobic
•Molecular and cytological evidence shows
them to be the ancestors of algal chloroplasts
Cyanobacteria—are true bacteria that acquired photosynthetic abilities, this trait is
monophyletic—Cyanobacteria are more closely related to each other than to other major
bacterial groups and can be traced to a common ancestor
Phylogeny based on 16D rRNA
After Olsen et al. 1994
Cyanobacteria are traditionally classified on the basis of morphology
Oscillatoriales
heterocystous forms are a monophyletic grouping within the cyanobacteria, but many
other morphological traits are polyphyletic
Contain heterocysts (N-fixing)
Prochlorophytes
Contain chlorophyll b—polyphyletic
Oscillatoria
Cladogram based on
16S rDNA sequence data
After Wilmotte 1994
filamentous forms on soft substrates,
mucillage sheaths, non-branching, capable
of oscillating motion--polyphyletic
A heterocyst (N-fixing cell) and neighboring vegetative cells
A heterocyst is a specialized thick-walled cell
with microplasmodesmata channels at each
end connecting it to neighboring cells
•Heterocyst walls reduce diffusion of gases, entry of gases occurs via channels from neighboring cells
•Glutamate enters from neighboring cells and is converted to glutamine in the presence of NH3
•The channels also allow fixed N (glutamine) to diffuse from the heterocysts to neighboring cells to be
converted back to glutamate—the amino groups can be used to form other amino acids (transamination)
•NH3 is formed from N2 by Nitrogenase using H-power from NADPH (glucose from neighboring cells)
After Haselkorn 1978.
Anabaena: cells in large colonies (filaments) with no gelatinous matrix, coiled or
straight, heterocysts and akinetes usually present, cells 3-5 microns
akinete
cell
Anabaena forms a mutualistic relationship with Azolla, an aquatic fern used in rice culture
•The leaves of this aquatic fern
have cavities that harbour
filamentous cyanobacteria
Anabaena azollae
•The large cells are heterocysts
•Traditional rice farming in many
countries involve planting Azolla to
build up N concentrations in rice
paddy.
Rivularia: cells in small whip-like tapered filaments (filaments) with no gelatinous
matrix, coiled or straight, heterocysts and akinetes usually present, cells 3-5 microns
Usually benthic or epiphytic
Akinete—resistant spore
Heterocysts
N2 fixing cell
Nostoc
Nostoc—a colonial cyanobacterium
Nostoc balls
mucilaginous matrix
http://biology.kenyon.edu/Microbial_Biorealm/bacteria/nostoc/PJnost2.jpg
Aphanizomenon Filaments aligned side-by-side to form dense sheet like
colonies, heterocysts and spores present, cells 4-6 microns
Microcystis: cells in large colonies irregularly arranged within a gelatinous matrix
Colony of Microcystis
A common bloom forming
cynabacterium that sometimes
can be highly toxic
No heterocysts, or N-fixing ability
Colonial growth pattern—cells
embedded in a gelatinous matrix
(3b)
Oscillatoria: unbranched filaments with
sheaths not conspicuous or extending
beyond the end of the filament,
heterocysts and akinetes absent
-Growing in very enriched locations
-usually on the substrate either on
rocks or in mud in lakes or rivers
-the filaments can move slowly back
and forth (oscillate) by vitue of
contractile glycoproteins—thus the
name
Lyngbya: unbranched filaments with sheaths extending beyond the filament
heterocysts or akinetes absent, cells 3-5 microns--Lyngbya
Lyngbya filaments in sheaths
often extending well beyond the
filaments
Stigonema: a cyanobacterium with true branched filaments, heterocysts present
Cells 4-6 microns
Scytonema: filaments have “false branching”—filaments emerge from the same
sheath—”false branching” eg
Scytonema is common on the
bottom of streams. Note false
branching in the filament
Heterocysts present
Cells around 10 microns
Absorbance
Chlorophyll b absorbs blue-green light the best—dominant wavelength
in deep water containing some organic matter
Phycobilins allow cyanobacteria to utilize green-yellow light
Energy from greenyellow wavelengths
is transferred to the
red absorption peak
of chlorophyll a
Each transfer step
yields a lower
energy photon
Phycobilosomes
(arrowheads)
attached to
membranes
Absorption spectra for cyanobacterial phycobilin
pigments found in phycobilosomes associated
with thylakoid membranes. From Gantt, 1975
Some important ecological attributes of cyanobacteria
Oldest photosynthetic organisms on earth still highly successful
Many can fix atmospheric Nitrogen (heterocysts), this allows them to compete well in Npoor environments, and also makes them useful in agroecosystems –eg rice culture
Most cyanobacteria grow best at fairly high temperatures and are among the best
competitors under the combination of high temperature (mid-summer) and high nutrient
conditions.
Because they do so well under nutrient rich conditions much of the periphyton
community in sewage outfalls is made up of cyanobacteria
Cyanobacteria are good at producing toxic substances. Usually this makes them
unpalatable to herbivores, and often it makes them highly toxic even to humans and
large mammals.
Cyanobacteria in lakes often cause noxious blooms. These smell bad and also cause
taste and odour problems in water supplies.
Cyanobacteria are famous for causing nuisance blooms in lakes—often float to the surface
Large planktonic Cyanobacteria colonies are sometimes buoyant—gas vesicles
Gas vesicles—
areas of low
density inside
the cytoplasm of
Nostoc spp.
From Waaland
and Branton
1969.
Gas vesicles form under low light
conditions→colonies to float upward.
Near the surface high photosynthesis
increases turgor pressure and vesicles
collapse→colonies sink downward