1. Structure
    1. Relatively large for bacteria
    2. Variety of organizations, including unicells, filaments, or packets of cells in mucilage.
      1. May form sheaths
    3. Gliding mobility, gas vesicles
    4. Some show marked cellular differentiation
      1. Heterocysts
        1. Thickened cell wall
        2. Often polar nodules at ends
        3. Site of Nitrogen fixation
        4. Cyclic phosphorylation only (keeps Oxygen concentration low)
        5. Iron is an essential cofactor for nitrogenase
      2. Akinetes
      3. Necridia
        1. Cell undergoes apoptosis Gives rise to hormogonia (short filaments for dispersal)
    5. Most have thylakoids (infoldings of the cell membrane)
    6. Most have phycobilisomes
    7. Cellular inclusions
      1. Gas vesicles
        1. Two proteins, GvpA & GvpC
        2. Form hollow shell
        3. Gas permeable, but not water permeable
        4. Collapse under pressure shock, but remain intact under vacuum
      2. Cyanophycean starch alpha-1,4 linked glucan (similar to glycogen & amylopectin)
      3. Cyanophycin granules
        1. Polymer of aspartate, with each aspartate linked to argenine
        2. Broken down under nitrogen limiting conditions
      4. Polyphosphate granules
        1. Storage of phosphate
        2. Stain with Toluidine Blue
      5. Carboxysomes
    8. Peptidoglycan cell wall (gram -)
  2. Photosynthesis
    1. Oxygenic Phototrophs
      1. Two photosystems, both Fe-S type and Quinone type
    2. At least two distinct pigmentation patterns are known:
      1. Chlorophyll a and phycobiliproteins (most cyanobacteria)
        1. Phycobiliproteins are arranged in phycobilisomes, hemispherical structures attached to photosystem II
          1. Phycoerythrin (Absorbtion maximum at 550 nm)
          2. Phycocyanin (Absorbtion maximum at 620 nm)
          3. Allophycocyanin (Absorbtion maximum at 650 nm)
          4. Photosystem I has membrane-integral LHCs
          5. Thylakoids are not stacked
        2. Chlorophyll a and b (Prochloron, Prochlorothrix, Prochlorococcus)
          1. Phycobilisomes are lacking, and thylakoids are stacked
          2. Originally mistaken for a separate group of bacteria, and mistakenly believed to be related to plastids
          3. Raven's hypothesis
      2. Can concentrate carbon with a carbonate pump (C1 pump)
        1. Use ATP to pump HCO3-, then convert HCO3- to CO2 (the form required by rubisco)
        2. Carboxysomes probably have both Carbonic Anhydrase and Rubisco
      3. Carbon fixation is by Calvin cycle
        1. Rubisco is form I (plant-like L8S8); form II rubisco is unknown in cyanobacteria
          1. Rubisco accumulates in polyhedral carboxysomes
        2. Food storage as cyanophycean starch
      4. Anoxygenic photosynthesis, using H2S as an electron donor, is also seen in some cases
      5. Microcoleus chthonoplastes
    3. Classification
      1. Now generally treated by bacterial code
        1. Originally treated by botanical code ("Blue-green Algae")
        2. It is very important to specify strain number
      2. Gloeobacter and Pseudoanabaena groups
        1. Gloeobacter
        2. Small, bacilliform
        3. Neither thylakoids nor phycobilisomes
        4. Phycobiliproteins line the inside of the plasma membrane, reminiscent of green bacteria
        5. Pseudoanabaena
      3. Plastid group
      4. Thermophilic unicellular group
        1. Synechococcus
      5. Synechocystis/Pleurocapsa/Microcystis group
        1. Prochloron (Chlorophylls a, b)
      6. Oscillatoria group
        1. Oscillatoria (grossly polyphyletic)
      7. Nostoc group
        1. Capable of nitrogen fixation
        2. Heterocyst - specialized cell type involved in N2 fixation
        3. Anabaena
        4. Nostoc
      8. Leptolyngbia group
      9. Phormidium group
      10. Synechococcus group
        1. Prochlorococcus marinus
      11. Incertae sedis
        1. Recently discovered cyanobacterium with Chlorophyll D -- looks like an intermediate between chlorophyll and bacteriochlorophyll
    4. Ecology
      1. Extremely important group
      2. Extraordinarily ancient fossil record
      3. Oxygenic photosynthesis
      4. Nitrogen fixation
        1. Trichodesmium - major N-fixer in open ocean
      5. Bloom forming
        1. Anabaena, Aphanizomenon, Microcystis
        2. Phosphate is typically the limiting nutrient in freshwater
        3. The most effective way of reducing cyanobacterial blooms is to reduce phosphate input
        4. Under some conditions, nitrogen supplements can shift balance toward more desirable algae
      6. Potentially toxic
      7. Found in a tremendous variety of environments
        1. Marine
        2. Freshwater
        3. Hotsprings (although only at relatively cool temperatures when compared with other photosynthetic bacteria)
        4. Found in fairly broad range of pH, but not in extremely acidic environments
        5. Soil
        6. Epiphytic
        7. Endolithic
        8. Symbiotic with lichens, protozoa

    Required Reading: M&K Chapter 1, VdH Chapters 2 and 3

    Supplementary Reading:

    The Prokaryotes; chapters 97, 98, 99.

    Raven, P.H. 1970. A multiple origin for plastids and mitochondria. Science 169:641-646.

    Turner, S. 1997. Molecular systematics of oxygenic photosynthetic bacteria. Pl. Syst. Evol. [Suppl] 11:53-86. (This article is Chapter 2 in D. Bhattacharya (ed.) 1997. Origins of Algae and their Plastids. Springer Wien/New York.)

    Wilmotte, A. 1994. Molecular evolution and taxonomy of the cyanobacteria. Pp. 1-25 in D.A Bryant (ed.), The Molecular Biology of the Cyanobacteria. Kluwer.