CYANOBACTERIA Flashcards
formerly called the blue green algae
Cyanobacteria
comprise a group of oxygenic photosynthetic prokaryotes
they lack membrane-bound nucleus and complex organelles.
Cyanobacteria
Cyanobacteria cell membrane is equipped with simple, flattened vesicles called
thylakoids
thylakoids contain _______ that enables them to release oxygen through photosynthesis much like algae and plants.
chlorophyll a
This release of oxygen by cyanobacteria had dramatically changed the earth’s atmosphere from a
reducing to an oxidizing
The cyanobacteria that successfully lived as symbiont in other prokaryotes also led to the evolution of photosynthetic eurkaryotes based on
endosymbiotic theory of the origin of eukaryotes
Recent molecular studies, however, now classified the prokaryotes under two domains
Bacteria and Archaea
Cyanobacteria occur in various body forms:
coccoid or unicellular, colonial and filamentous.
occur singly
coccoid or unicellular forms
voluminous and fluffy covering found surrounding the cells of cyanobacteria
mucilaginous sheath
comprises the cellulose fibers aligned reticulately within the matrix
mucilaginous sheath
multicellular form
Such filamentous forms may either have true branching or false branching filament
trichomate or filamentous forms
in colonies of two or more cells enclosed in a gelatinous or mucilaginous sheath.
Colonial
composed of a single row of cells
uniseriate
composed of several rows of cells, bracnhed
multiseriate
with similar cells
homocystous
with specialized cell called heterocyst or heterocyte for nitrogen fixation
heterocytous
cyanobacteria are traditionally classified under five orders
Order Chroococcales
Order Pleurocapsales
Order Oscillatoriales
Order Nostocales
Order Stigonematales
solitary cells, aggregations and colonies not reproducing by spores
Order
Order Chroococcales
solitary cells, aggregations and short filaments reproducing by spores
Order
Order Pleurocapsales
unbranched homocystous filaments, i.e. without heterocysts and akinetes
Order
Order Oscillatoriales
unbranched filaments with heterocysts and akinetes
order
Order Nostocales
branched filaments (sometimes multiseriate) with heterocysts and akinetes
Order Stigonematales
orders that are yet to be supported by phylogenetic studies
Order Chroococcales Order Pleurocapsales Order Oscillatoriales
but the 2 orders of heterocystous cyanobacteria have now been found to be a monophyletic group based on the 16S rRNA analysis.
(Nostocales and Stigonematales)
class of cyanobacteria
Gloeocapsa.
Oscillatoria.
Spirulina.
Anabaena.
Nostoc.
Rivularia.
relatively simple cyanobacterium
spherical cells either grow singly or in small aggregations (=colonies) held together by a firm mucilaginous sheath
The sheath is often colored and has distinct layers that delineate each cell’s contribution.
Reproduction is carried out by simple binary fission.
Gloeocapsa
filamentous cyanobacterium consists of a single series of similar cells (homocystous)
shorter than wide except for terminal cells with a modified shape.
mucilaginous sheath encloses the filament
Reproduction is achieved via fragmentation
Oscillatoria.
often grows in mats or interwoven filaments that may show active gliding or “oscillating” movement to adjust filament density in a mat in response to environmental conditions.
Oscillatoria
proposed reason of Oscillatoria movement
mucilage secretion
part of a filament Oscillatoria breaks off producing short segments
hormogonia.
oftentimes distinguishable by their cell shape, greater motility and presence of gas vesicles, detach from vegetative filaments at separation discs.
grow by adding new cells.
hormogonia.
his filamentous, homocytous cyanobacterium is easily distinguishable by its spiral trichome, which lacks a mucilagenous sheath. The high protein content merits its being a food supplement.
Spirulina.
filamentous cyanobacterium forming heterocysts
unbranched filaments appear like a string of beads.
Anabaena
specialized cells for N2 fixation
heterocysts
thick-walled cells formed after a period of active growth that survive in a dormant state when conditions are unfavorable for further growth
akinetes
Both are larger and with thicker walls than the vegetative cells.
heterocysts and akinetes
differ from heterocysts in having granular cytoplasm with an abundance of cyanophycin granules
Akinetes
This cyanobacterium is much similar with Anabaena, but has a thick and firm mucilaginous sheath which may enclose the filaments into highly visible colonies
Nostoc.
highly visible colonies of Nostoc
This particular species is highly nutritious.
Nostoc commune
This forms colonies in which the sheaths of one filament are confluent with others. The sheaths are heavily encrusted with lime and are very firm.
the filaments are polarized with a terminal heterocysts under conditions of low nitrogen concentration. When grown in media containing nitrogenous compounds, heterocysts are not formed and the trichomes are not tapered, thus, resembling species of genera such as Oscillatoria.
Rivularia.
