Culture of photomixotrophic soybean and pine in a modified fermentor using a novel impeller

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Abstract
Photomixotrophic suspensions of Glycine max (soybean) and Pinus elliottii (slash pine) have been successfully cultured in a hybrid stirred tank photobioreactor using a novel cell-lift impeller. A cell-lift impeller exhibited cell viabilities over 90% and an average cell aggregate size of 1.0 mm or less. Flat-bladed turbines produced equivalent biomass to the cell-lift impeller, but cell viability was reduced (85%) and cell aggregate size increased (3–5 mm diameter). Maximum fresh weights of 82 g L−1 (soybean) and 52 g L−1 (slash pine) were achieved in 15 days using continuous lighting (90–100 μE m−2 s−1) and supplemental 2% CO2 inlet gas. Maximum biomass was achieved using an impeller speed of 60 rpm with air-flow rate of 0.2 vvm for the cell-lift impeller and the pair of flat bladed turbines. The lag and early exponential phases were characterized by (1) rapid hydrolysis of sucrose followed by preferential use of glucose and (2) a reduction in chlorophyll levels. Carbon dioxide (2%–5%) was an essential nutrient for photomixotrophic cell culture in the bioreactors.