Kelly 19 - Cyanobacteria Flashcards
Give 4 properties of cyanobacteria
- fix CO2 in the Calvin cycle - photoautotrophs (photosynthetic)
- complex differentiation & polymorphic cell cycles that are determined by nutrient availability (Nitrogen)
- gliding motility w/ no flagella
- ## fix atmospheric N2 to NH4+ ions using nitrogenase enzyme
How many major groups of cyanobacteria are there and name the most complex group
4
heterocystous
Draw a the filamentous structure of the heterocystous group (include a heterocyst)
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When are heterocysts produced and what are their function
under low environmental conditions of NH4+
convert atmosphere N2 to NH4+ ions using nitrogenase
NH4+ produced then passes into surrounding vegetative cells
Give 3 properties of the heterocyst
- terminally differentiated - will not divide any more
- do not fix CO2 in Calvin cycle
- use nitrogenase to fix N2
Given that cyanobacteria perform oxygenic
photosynthesis, how can nitrogenase function in heterocysts?
heterocysts have thick outer envelopes that resists the entry of O2 into the heterocyst by diffusion
only have PSI , no O2 production
Draw the schematic diagram that highlights how the Photosystems of heterocysts differ from vegetative cels
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Where does nitrogenase obtain its ATP and e- from?
either from vegetative/heterocyst & which part of process
ATP - heterocyst - formation of ATP via formation of PMF from cyclic e- transport chain
e- - vegetative cell, PSI donates e- to ferredoxin e- carrier and donates to nitrogenase
How would we get a synchronous population of heterocyst formation?
transfer cyanobacteria from high NH4+ conc medium to a low NH4+ conc medium
get formation of new heterocysts @ same time
Name the genetic tools that can be used to study heterocyst differentiation
- Tn5/chemical mutagenesis
- gene fusions
- genome sequencing
- conjugation (NOT transformation)
Describe the difference between conjugation @ transformation
conjugation involves formation of pilli to connect cells and transformation does not
Describe the process of creating a gene fusion to study levels of gene expression in heterocyst formation
- cyanobacteria POI is fused upstream of reporter gene on plasmid vector
- reporter gene eg LuxAB encodes LUCIFERASE (uses a substrate & reductant to emit green light - however relies on cell being metabolically active) also eg = gfp (GREEN FLUORESCENT PROTEIN)
- conjugation of plasmid vector into cyanobacteria
- using light microscopy, look for any colour being emitted @ if ONLY in heterocysts then we know this gene only expressed in heterocysts
Describe how heterocysts form and the genes that regulate its production
NtcA senses low NH4+ in envionment (low ratio of NH4+:2-oxoglutarate)
Activates HetR protein & both proteins increase their levels of expression in a feedback mechanism
HetR (DNA binding protein) binds to het gene promoters including HetN - stops heterocyst production in nearby vegetative cells
het genes also involved in producing the envelope proteins surrounding the het to limit O2 diffusion in
now we have a functioning heterocyst that exports NH4+ and import C sources
Describe how the production of nitrogenase is regulated in VEG/HET cells
nifKDH operon encodes nitrogenase
FdxN encodes Fd and can interact w/ nitrogenase
in veg;
- 11kb insertion in nifD gene
- 55kb insertion in FdxN gene
in het:
- XisF and XisA are encoded which excise the inserted DNA and create functional NifD and FdxN genes
What is the difference between FdxN ferredoxin and the major Ferredoxin found in veg cells
Fd from veg cells transfers the electrons to FdxN in heterocysts which can then interact with the nitrogenase
