Effects of light and temperature on the photoautotrophic growth and photoinhibition of nitrogen-fixing cyanobacterium Cyanothece sp. ATCC 51142

The unicellular, nitrogen-fixing cyanobacterium Cyanothece sp. ATCC 51142 is a promising strain with a remarkable capability of producing large quantities of hydrogen, an energy carrier long being promoted as an ideal fuel. Under extreme environmental conditions, significant reduction of cellular photosynthetic capability is commonly observed in algae and cyanobacteria. Even less severe conditions can induce photo-inhibitive growth dynamics, which in turn result in a marked decrease in biomass and gas productivities. In this study a detailed analysis of the effect of two extrinsic parameters, namely light intensity and temperature, on the photoautotrophic growth of Cyanothece was performed in order to reveal critical conditions that would lead to undesired photoinhibition. A high degree of coherence between cyanobacterial growth and nutrient uptake kinetics was observed, as well as a strong dependence on the change of the two parameters. Nitrogen depletion was confirmed as a trigger, which transforms an exponential into a stationary growth phase. A non-linear relationship between the maximum specific growth rate and the irradiance up to 320 μE m− 2 s− 1 was identified and found to be dominated by light saturation rather than photoinhibition. The relationship between the specific growth rate and the temperature was found to be linear until a remarkable drop in the final biomass productivity and cyanobacterial photosynthetic capability was observed at 40 °C. The cause of this is a high temperature-induced photoinhibition effect.