Microbial photosynthesis presents a valuable opportunity to capture abundant light energy to produce renewable bioenergy and biomaterials. To understand the factors that control the productivity of photosyntheticmicroorganisms, we conducted a series of semi-continuous experiments using bench-scale photobioreactor (PBR) systems, the cyanobacterium Synechocystis PCC6803 (PCC6803), and light conditions imitating actual day-night light irradiance (LI). Our results demonstrate that using normal BG-11 medium resulted in severe phosphate (Pi) limitation for continuous operation. Mitigation of Pi-limitation, by augmenting the Pi content of BG-11, allowed higher biomass productivity; however, once Pi-limitation was alleviated, limitation by inorganic carbon (Ci) or LI occurred. Ci-limitation was detected by a low total Ci concentration (<5mgC/L) and high and fluctuating pH. Ci-limitation was relieved by delivering more CO2, which led to a stable pH in the range of 7-9 and at least 5mg/L of Ci in HCO3-. LI limitation, evidenced by an average LI <14W/m2 for PCC6803, was induced by a high biomass concentration of 1,300mg/L. Thus, this work provides quantitative tools of stoichiometry and kinetics to evaluate limitation on PBRs.
- Inorganic carbon limitation
- Light irradiance limitation
- Phosphorus limitation
- Photoautotrophic biomass production
- Rate-limiting factors
ASJC Scopus subject areas
- Applied Microbiology and Biotechnology