Photonfluxostat: A method for light-limited batch cultivation of cyanobacteria at different, yet constant, growth rates

The growth rate and physiology of photoautotrophic bacteria are dependent on the incident light color and intensity. Here we report a widely applicable and straightforward method for light-limited batch cultivation of phototrophic bacteria at different, yet constant, growth rates. We illustrate its usage with Synechocystis sp. PCC6803, a model cyanobacterium used as a chassis for sustainable cell-factories and capable of turning CO2 into commodity products. The cultivation method we developed resembles a 'photonfluxostat'. It enables the setting of the growth rate of phototrophs during batch cultivation by adjustment of the illumination intensity ('photon dosing'). Using this method to study the growth-rate response of Synechocystis, we found that while the cell volume increased, the chlorophyll a content and the PSI/PSII ratio decreased, as growth rate increased. This method allows for a quantitative and controlled study of the light-dependent physiology of phototropic bacteria, a highly relevant group of bacteria for modern biotechnology.