Cell Biology of Cyanobacteria

Conrad Mullineaux
Professor of Microbiology
School of Biological and Chemical Sciences
Queen Mary, University of London
Mile End Road,
London E1 4NS
UK

The cyanobacterium Synechocystis 6803 is a favourite model organism for genetic manipulation. It is naturally transformable, it can grow heterotrophically as well as phototrophically, and it was the first photosynthetic organism to have its genome completely sequenced. It has roughly spherical cells about 2 - 3.5 microns across


Thin-section electron micrograph of Synechocystis 6803. Note the thylakoid membranes (irregular loops of membrane in the cytoplasm). The dark spots on the membrane surface are phycobilisomes.


Scanning electron micrographs of Synechocystis 6803. All electron micrographs courtesy of Anna Law and Iain Wilson, NIMR Mill Hill


Although the cells of Synechocystis (and most other cyanobacteria) are relatively small, it is still possible to use fluorescence microscopy to get information on the distribution of cell components in living cells. Genetic tagging of specific proteins with Green Fluorescent Protein (GFP) allows the distribution and mobility of those proteins to be visualised in living cells, in real time. This gives us an exciting new way to study the biochemistry and cell biology of cyanobacteria. Currently using this approach in my lab are:

  • Dr Samantha Bryan, who is funded by BBSRC to investigate the biogenesis of thylakoid membranes
  • Dr Lu-ning Liu who holds a Marie Curie fellowship and is working mainly on the localisation of electron transport complexes
  • Joanna Sacharz, a PhD student and early-stage researcher funded by the HARVEST network, who is working on proteins involved in the repair of Photosystem II.
    See also our work on cell communication and dynamics of photosynthetic membranes in cyanobacteria.

    Confocal fluorescence micrographs of Synechocystis cells in which the FtsH (slr0228) protease has been tagged by gene fusion. Scale-bars are 5 microns. Green fluorescence is from GFP, red fluorescence is from the photosynthetic pigments in the thylakoid membranes and a merged image is shown below. The overlap of red and green fluorescence shows that FtsH is located in the thylakoids, where it plays a key role in the repair of Photosystem II. Collaboration with Myles Barker and Peter Nixon (Imperial college) Ref: Komenda et al (2006).



    Confocal fluorescence images of Synechocystis cells expressing GFP fused to a TAT signal sequence (collaboration with Colin Robinson, University of Warwick). GFP fluorescence in green, fluorescence from the photosynthetic pigments in red. A merged image is shown on the right. The TAT pathway exports GFP to the periplasm (shown by the green "halo" of fluorescence surrounding the cytoplasm). Ref: Spence et al (2003)

    Some key publications on this topic:
    Spence, E., Sarcina, M., Ray, N., Møller S.G., Mullineaux, C.W.and Robinson, C. (2003) Membrane-specific targeting of green fluorescent protein by the Tat pathway in the cyanobacterium Synechocystis PCC6803. Mol Microbiol. 48, 1481-1489.

    Komenda, J., Barker, M., Kuvikova, S., De Vries, R., Mullineaux, C.W., Tichy, M. and Nixon, P.J. (2006) The FtsH protease, slr0228, is important for quality control of the thylakoid membrane of Synechocystis PCC6803. J. Biol. Chem. 281, 1145-1151.