lecture 3 (cyanobacteria)

Question 1

some cyanobacteria form large mound shaped structures. what are these called? what are they made of?

Answer 1

they are called stromatolites (can also get microbialites and strombolites)
made of layers of calcareous materials

Question 2

what is characteristic of the environment where these modern cyanobacteria formations are found?

Answer 2

marine, hyper saline, low latitudes and lakes

Question 3

how old is the oldest microfossil and what was it

Answer 3

cyanobacteria, 2.3-2.45 bya

Question 4

describe the different types of cyanobacteria thallus structure (7)

Answer 4

unicells, colonies, unbranched filaments, unbranched forms with specialized cells, aggregations of multiple trichomes in a common sheath, false branched, true branched

Question 5

what is a trichome

Answer 5

an unbranched filament

Question 6

what was the first cyanobacteria discovered (when and how)?

Answer 6

coccoid cyanobacteria (synechococcus): solitary or clusters, very abundant, large cells. discovered in 1980’s from intense orange phycoerythrin fluorescence

Question 7

what was the second cyanobacteria discovered (when and how)?

Answer 7

prochlorophytes (prochlorococcus) smallest known photoautotroph. smaller and fainter fluorescence. detected later in 1980’s from dim red fluorescence emitted by unique pigments

Question 8

define multicellularity

Answer 8

complexity/specialized cells, intercellular communication

Question 9

exospores

Answer 9

spore generated on the end of a filament on the outside

Question 10

endospores

Answer 10

spore generated on the inside of end of a filament (opens up to release)

Question 11

separation disks

Answer 11

cells that die to seperate filaments

Question 12

akinetes

Answer 12

large, oval shaped resting cell

Question 13

heterocyte

Answer 13

round, small cell, site of nitrogen fixation

Question 14

draw a diagram with the different layers of cyanobacterial cell wall

Answer 14

surrounded by lipopolysaccharide envelope. outer most is protein fibrils, then s-layer, , outer membrane, peptidoglycan layer, inner membrane, cytoplasm

Question 15

what does mucilage sheath do for cyanobacteria?

Answer 15

capture scare micronutrients, aid in buoyancy, deter herbivores, harbor bacterial associates, absorba UV radiation/allow them to live in exposed environments

Question 16

describe cyanobacteria thylakoids arrangement and location

Answer 16

not stacked, arranged concentrically at cell perifery

Question 17

describe the 3 known modes of motility in cyanobacteria

Answer 17

no flagella, can swim using surface proteins(no phototaxis), gliding by extrusion of mucilage/protein extensions (phototaxis), buoyancy regulation through gas vesicles

Question 18

what photosynthetic pigments are present in cyanobacteria?

Answer 18

chl a, chl d, carotenoids (xanthophylls and beta carotene) and phycobilins in all but prochlorophytes

Question 19

what are the three phycobilins and where are they found?

Answer 19

found in phycobilisomes
phycoerythrin, phycocyanin and allophycocyanin (in this order)

Question 20

what is chromatic acclimation

Answer 20

altering pigment composition in response to light quality

Question 21

why are cyanobacteria so successful at all PAR levels?

Answer 21

they have phycobilins and can do chromatic acclimation

Question 22

what is the mode of reproduction in filamentous cyanobacteria?

Answer 22

(no sexual reproduction), produce hormogonia (short, motile filaments from breakup of longer filaments)

Question 23

what is the storage product in Cyanobacteria?

Answer 23

cyanophycean starch

Question 24

what triggers and inhibits N2 fixation?

Answer 24

triggered by low NH4 and NO3 (energetically expensive process, only done when needed)
inhibited by high O2

Question 25

what is the name of the cells specialized for N2 fixation and their roles in this process?

Answer 25

heterocytes, these reduce O2 toxicity effects on nitrogenase by reducing oxygen levels

Question 26

describe two adaptations/strategies that cyanobacteria without specialized cells can use to fix N2

Answer 26

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)

Question 27

breifly explain the process of N2 fixation in cyanobacteria with heterocytes:

Answer 27

heterocyte reduces O2, has no photosystem 2 expression. uses photosystem 1 to produce ATP, importing carbohydrates through microplasmodesmata (no C fixation here).

Question 28

describe differences and similarities between akinetes and heterocytes

Answer 28

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

Question 29

morphological figures used to define cyanobacteria taxonomy

Question 30

examples of extreme environments cyanobacteria can grow in

Answer 30

hot springs/thermal pools, alkaline waters, cold deserts, frozen waters, porous sandstone/limestone rocks in arid, hot deserts, soil surfaces, hypersaline waters etc.