The primary goal of the project is to study the photosynthesis of marine diazotrophic cyanobacteria, with particular focus on i) daily and depth-dependent changes in underwater light conditions, and ii) the dependence of photosynthetic and closely related cellular activities on light wavelength. We have chosen the single-celled model cyanobacterium Crocosphaera watsonii as the subject of our investigations.
Under natural conditions, due to the natural movement of the water column, C. watsonii cells occur at constantly changing water depths (0-50 m) – and the intensity of the light reaching them changes accordingly: for example, only about 10% of the light reaching the surface reaches a depth of 50 m. The intensity of light reaching C. watsonii cells thus depends both on the time of day and water depth. To model this under laboratory conditions, we regulate the illumination accordingly using a custom written software. The control cultures are illuminated with constant light so the average daily light intensity is the same in both cases.
Not only the intensity of light, but also its color changes significantly with water depth. The red and violet components of light are absorbed at shallower depths, with only blue and green light reaching the deeper water layers. The change in light color depending on water depth is also modeled under laboratory conditions using a so-called multicultivator system, where C. watsonii cells are grown under different colored lighting.