Photoautotrophic Cell and Tissue Culture in a Tubular Photobioreactor

An externally illuminated tubular photobioreactor was constructed from 3.4 m stainless steel tubes and 22.1 m glass tubes for the cultivation of photoautotrophic organisms. The 30‐L reactor can be equipped with helical static mixers in order to create a uniform radial exchange within the tubes, 40 mm in diameter. A flexible construction of the reactor allows scale‐down experiments to be carried out with axial velocities between 0.3–2.5 m/s, gassing‐in rates of 0–0.5 L/min, k_L a values of 0.002–0.006 s^–1 and six metal halide lamps inducing photon flux densities in the range of 70–300 μE/m²s. Two model organisms, the green microalgae Chlorella vulgaris and the bryophyte Physcomitrella patens, were chosen to characterize cell growth and physiology in submerse cultures. Comparative experiments with Chlorella vulgaris in two configurations of the reactor with inserted helical static mixers and plates resulted in maximum growth rates of 1.6 d^–1. No growth enhancement was obtained in the case of helical static mixers at a mean PFD of 150 μE/m²s and an axial velocity of 0.4 m/s. No homogenous flow could be obtained in the case of inserted plates. Physcomitrella patens was successfully cultivated in the reactor (μ = 0.36 d^–1), whereas average axial velocities of ca. 0.6 m/s guarantee favorable gas transport without contributing to cell damage. This makes tubular photobioreactors a promising production system for the production of glycosylated recombinant proteins derived from moss.