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Biotechnol Bioeng. 2010 Jul 1;106(4):553-63. doi: 10.1002/bit.22724.

Photoautotrophic nutrient utilization and limitation during semi-continuous growth of Synechocystis sp. PCC6803.

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Center for Environmental Biotechnology, Biodesign Institute, Arizona State University, Tempe, Arizona 85287-5701, USA.


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 photosynthetic microorganisms, 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 (P(i)) limitation for continuous operation. Mitigation of P(i)-limitation, by augmenting the P(i) content of BG-11, allowed higher biomass productivity; however, once P(i)-limitation was alleviated, limitation by inorganic carbon (C(i)) or LI occurred. C(i)-limitation was detected by a low total C(i) concentration (<5 mg C/L) and high and fluctuating pH. C(i)-limitation was relieved by delivering more CO(2), which led to a stable pH in the range of 7-9 and at least 5 mg/L of C(i) in HCO(3)(-). LI limitation, evidenced by an average LI <14 W/m(2) for PCC6803, was induced by a high biomass concentration of 1,300 mg/L. Thus, this work provides quantitative tools of stoichiometry and kinetics to evaluate limitation on PBRs.

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