Regulation of phototaxis in cyanobacteria and how a small cell can detect the direction of light

The unicellular cyanobacterium Synechocystis 6803 uses type IV pili for phototactic motility. Regulation of phototaxis involves many different gene products, including various photoreceptors, second messengers and the RNA chaperone Hfq. Here, I will present our recent research on phototaxis control and how Synechocystis cells directly and accurately sense the position of a light source. We use a range of optical techniques to show that directional light sensing is possible because the spherical cells of Synechocystis work like microscopic lenses focusing a sharp image of the light source at the non-illuminated side of the cell. Our investigations with other bacteria indicate that such micro-optic effects are not confined to spherical cyanobacteria, or even to phototrophs.