Analysis of the light intensity dependence of the growth ofSynechocystisand of the light distribution in a photobioreactor energized by 635 nm light

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.

Quantitative insights into the cyanobacterial cell economy

“…Under the highest intensity of 1100 μmol(photons) m -2 s -1 , the specific growth rate decreased to true0μ=0.093±0.011thinmathspacenormalh−1, corresponding to a doubling time of true0TD=7.5thinmathspaceh (Figure 1C–D). The growth curve is consistent with previous measurements of cyanobacterial growth (Zavřel et al, 2015b; Cordara et al, 2018) and can be subdivided into three phases: light-limited, light-saturated, and photoinhibited growth.…”

“…The increase in gas exchange (O 2 release and basal respiration) has been observed previously (Zavřel et al, 2015b; Zavřel et al, 2017). Likewise, the increase in cellular size with growth rate (Figure 2A) has been reported in Synechocystis (Zavřel et al, 2017; Cordara et al, 2018) as well as in heterotrophic bacteria, yeast or mammalian cells (Aldea et al, 2017). Light was also shown to affect DNA content (ploidy level) in Synechocystis (Zerulla et al, 2016), however, no study of DNA content change with growth rate is available to date.…”

Quantitative insights into the cyanobacterial cell economy

“…Under the highest intensity of 1100 µmol(photons) m −2 s −1 , the specific growth rate decreased to µ = 0.093 ± 0.011 h −1 , corresponding to a doubling time of T D = 7.5 h ( Figure 1C-D). The growth curve is consistent with previous measurements of cyanobacterial growth (Zavřel et al, 2015b;Cordara et al, 2018) and can be subdivided into three phases: light-limited, lightsaturated, and photoinhibited growth.…”

“…The increase in gas exchange (O 2 release and basal respiration) has been observed previously. Likewise, the increase in cellular size with growth rate (Figure 2A) has been reported in Synechocystis (Zavřel et al, 2017;Cordara et al, 2018) as well as in bacteria, yeast or mammalian cells (Aldea et al, 2017). Light was also shown to affect DNA content (ploidy level) in Synechocystis (Zerulla et al, 2016), however, no study of DNA content change with growth rate is available to date.…”

The potential of quantitative models to improve microalgae photosynthetic efficiency

“…The latter models, which are capable of capturing the key photosynthetic dynamics, can be exploited to estimate how photosynthetic activity changes in distinct parts of the culture, starting from the light distribution and the dependence of photosynthetic performances from illumination (Simionato et al , Alboresi et al , Meneghesso et al , Cordara et al ; Fig. ).…”