lecture 3 (cyanobacteria) Flashcards
some cyanobacteria form large mound shaped structures. what are these called? what are they made of?
they are called stromatolites (can also get microbialites and strombolites)
made of layers of calcareous materials
what is characteristic of the environment where these modern cyanobacteria formations are found?
marine, hyper saline, low latitudes and lakes
how old is the oldest microfossil and what was it
cyanobacteria, 2.3-2.45 bya
describe the different types of cyanobacteria thallus structure (7)
unicells, colonies, unbranched filaments, unbranched forms with specialized cells, aggregations of multiple trichomes in a common sheath, false branched, true branched
what is a trichome
an unbranched filament
what was the first cyanobacteria discovered (when and how)?
coccoid cyanobacteria (synechococcus): solitary or clusters, very abundant, large cells. discovered in 1980’s from intense orange phycoerythrin fluorescence
what was the second cyanobacteria discovered (when and how)?
prochlorophytes (prochlorococcus) smallest known photoautotroph. smaller and fainter fluorescence. detected later in 1980’s from dim red fluorescence emitted by unique pigments
define multicellularity
complexity/specialized cells, intercellular communication
exospores
spore generated on the end of a filament on the outside
endospores
spore generated on the inside of end of a filament (opens up to release)
separation disks
cells that die to seperate filaments
akinetes
large, oval shaped resting cell
heterocyte
round, small cell, site of nitrogen fixation
draw a diagram with the different layers of cyanobacterial cell wall
surrounded by lipopolysaccharide envelope. outer most is protein fibrils, then s-layer, , outer membrane, peptidoglycan layer, inner membrane, cytoplasm
what does mucilage sheath do for cyanobacteria?
capture scare micronutrients, aid in buoyancy, deter herbivores, harbor bacterial associates, absorba UV radiation/allow them to live in exposed environments
describe cyanobacteria thylakoids arrangement and location
not stacked, arranged concentrically at cell perifery
describe the 3 known modes of motility in cyanobacteria
no flagella, can swim using surface proteins(no phototaxis), gliding by extrusion of mucilage/protein extensions (phototaxis), buoyancy regulation through gas vesicles
what photosynthetic pigments are present in cyanobacteria?
chl a, chl d, carotenoids (xanthophylls and beta carotene) and phycobilins in all but prochlorophytes
what are the three phycobilins and where are they found?
found in phycobilisomes
phycoerythrin, phycocyanin and allophycocyanin (in this order)
what is chromatic acclimation
altering pigment composition in response to light quality
why are cyanobacteria so successful at all PAR levels?
they have phycobilins and can do chromatic acclimation
what is the mode of reproduction in filamentous cyanobacteria?
(no sexual reproduction), produce hormogonia (short, motile filaments from breakup of longer filaments)
what is the storage product in Cyanobacteria?
cyanophycean starch
what triggers and inhibits N2 fixation?
triggered by low NH4 and NO3 (energetically expensive process, only done when needed)
inhibited by high O2
what is the name of the cells specialized for N2 fixation and their roles in this process?
heterocytes, these reduce O2 toxicity effects on nitrogenase by reducing oxygen levels
describe two adaptations/strategies that cyanobacteria without specialized cells can use to fix N2
N2 fixation at night/under anaerobic conditions, or by downregulating photosystem 2, or division of labour (outer portion of mat photosynthesizes, inner does N2 fixation)
breifly explain the process of N2 fixation in cyanobacteria with heterocytes:
heterocyte reduces O2, has no photosystem 2 expression. uses photosystem 1 to produce ATP, importing carbohydrates through microplasmodesmata (no C fixation here).
describe differences and similarities between akinetes and heterocytes
heterocytes: small round cell, N fixation, thick mucilage and walls with polysaccharides, deactivated photosystem 2, pale green/colourless
akinetes: resting cells, thick walls with polysaccharides, large cell, abundant storage granules, no N fixation, deactivated photosystem 2
morphological figures used to define cyanobacteria taxonomy
examples of extreme environments cyanobacteria can grow in
hot springs/thermal pools, alkaline waters, cold deserts, frozen waters, porous sandstone/limestone rocks in arid, hot deserts, soil surfaces, hypersaline waters etc.
