Abstract
Synechocystis gathered momentum in modelling studies and biotechnological applications owing to multiple factors like fast growth, ability to fix carbon dioxide into valuable products, and the relative ease of genetic manipulation. Synechocystis physiology and metabolism, and consequently, the productivity of Synechocystis-based photobioreactors (PBRs), are heavily light modulated. Here, we set up a turbidostat-controlled lab-scale cultivation system in order to study the influence of varying orange–red light intensities on Synechocystis growth characteristics and photosynthetic activity. Synechocystis growth and photosynthetic activity were found to raise as supplied light intensity increased up to 500 μmol photons m−2 s−1 and to enter the photoinhibition state only at 800 μmol photons m−2 s−1. Interestingly, reverting the light to a non-photo-inhibiting intensity unveiled Synechocystis to be able to promptly recover. Furthermore, our characterization displayed a clear correlation between variations in growth rate and cell size, extending a phenomenon previously observed in other cyanobacteria. Further, we applied a modelling approach to simulate the effects produced by varying the incident light intensity on its local distribution within the PBR vessel. Our model simulations suggested that the photosynthetic activity of Synechocystis could be enhanced by finely regulating the intensity of the light incident on the PBR in order to prevent cells from experiencing light-induced stress and induce their exploitation of areas of different local light intensity formed in the vessel. In the latter case, the heterogeneous distribution of the local light intensity would allow Synechocystis for an optimized usage of light.
Highlights
Monitoring Synechocystis physiological state under varying light regimes, we found that growth rate, cell size and Photosystem II (PSII) activity were influenced by light intensity, albeit in slightly different ways
We measured Synechocystis growth rate to evaluate its generation time, and the amount of oxygen dissolved in the medium, which provides an indication of the PSII activity within cell (Schuurmans et al, 2015)
Since this efficiency largely depends on the cyanobacteria ability to manage the light collected in the cultivation apparatus, in this work we thoroughly investigated the impact of the setup of the light conditions in the PBR on Synechocystis growth and photosynthetic activity
Summary
Synechocystis has attracted much interest as model organism in product-oriented industrial biotechnology due to the ability to effortlessly recycle carbon dioxide (CO2) into valuable fuels and chemicals, the simplicity of its culture conditions, the ease of genetic manipulation and its relatively fast cell growth compared to higher plants (Janssen et al, 2003; Angermayr, Hellingwerf & Teixeira De Mattos, 2009). Synechocystis has served in many genetic engineering studies as biofactory for the production of a variety of products (Yu et al, 2013; Singh et al, 2017), such as ethanol (Gao et al, 2012), isobutanol (Varman et al, 2013), lactate (Angermayr, Paszota & Hellingwerf, 2012; Joseph et al, 2013) and polyhydroxyalkanoate (Luengo et al, 2003), which can be widely utilized in biotechnology and industrial fields
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