Cyanobacteria use micro-optics to sense light direction

Area of Science:

• Microbiology
• Biophysics
• Cell Biology

Background:

• Bacterial phototaxis, the directed movement of bacteria in response to light, has been known for over a century.
• The precise mechanism by which small cells like cyanobacteria sense light direction remained unclear.
• Synechocystis sp. PCC 6803, a unicellular cyanobacterium, utilizes Type IV pili for motility and possesses various photoreceptors.

Purpose of the Study:

• To elucidate the mechanism of directional light sensing in individual Synechocystis cells.
• To determine if cells respond to light gradients or directly sense light source position.
• To investigate the role of cell structure in phototaxis.

Main Methods:

• Observing individual Synechocystis cell behavior in response to controlled light stimuli.
• Analyzing cellular responses to different light intensity patterns and source positions.
• Microscopic imaging to understand light focusing within the cell.

Main Results:

• Synechocystis cells do not respond to spatiotemporal light intensity gradients.
• Cells directly and accurately sense the position of a light source.
• The spherical shape of Synechocystis cells functions as a microlens, focusing light.
• Focused light on the cell edge opposite the source triggers movement away from the focal point.

Conclusions:

• Synechocystis cells employ a unique 'camera eye' mechanism for directional light sensing.
• The cell's spherical geometry is crucial for focusing light and enabling phototaxis.
• This finding represents a novel biological mechanism for light detection in microorganisms.