Synechococcus sp. (PTCC 6021) cultivation under different light irradiances-Modeling of growth rate-light response

Synechococcus sp. (PTCC 6021), a cyanobacterium species, was cultivated in an internally illuminated photobioreactor. The reactor was designed to achieve a monoseptic cultivation of the species. The goal was to study the growth-irradiance behavior of Synechococcus sp. (PTCC 6021). To accomplish this, different initial light irradiances were implemented inside the photobioreactor and the growth of the cells was monitored. It was observed that cell growth increased with higher light intensity until the photoinhibition occurrence at light irradiance higher than 250 μE m(-2) s(-1). The maximum OD600, maximum growth rate, and biomass productivity increased, and hence the extinction coefficient decreased, with the increase in light irradiance before photoinhibition. The maximum optical density (OD600) of 5.91 was obtained with irradiance below 250 μE m(-2) s(-1) during a growth period of 80 days. The modified Monod function could model the growth-irradiance of cells with satisfactory agreement with the experimental data. The comparison of growth-irradiance of the studied species with other photosynthetic organisms showed the same trend as for cyanobacteria with photoinhibition.