  The ability to cultivate the cyanobacterium Arhtrospira platensis in
artificially lightened photobioreactors using high energetic efficiency
(quasi-monochromatic) red LED was investigated. In order to reach the same
maximal productivities as with the polychromatic lightening control conditions
(red + blue, P/2e- = 1.275), the need to work with an optimal range of
wavelength around 620 nm was first established on batch and continuous
cultures. The long-term physiological and kinetic behavior was then verified in
a continuous photobioreactor illuminated only with red (620 nm) LED, showing
that the maximum productivities can be maintained over 30 residence times with
only minor changes in the pigment content of the cells corresponding to a
well-known adaptation mechanism of the photosystems, but without any effect on
growth and stoichiometry. For both poly and monochromatic incident light
inputs, a predictive spectral knowledge model was proposed and validated for
the first time, allowing the calculation of the kinetics and stoichiometry
observed in any photobioreactor cultivating A. platensis, or other
cyanobacteria if the parameters were updated. It is shown that the photon flux
(with a specified wavelength) must be used instead of light energy flux as a
relevant control variable for the growth. The experimental and theoretical
results obtained in this study demonstrate that it is possible to save the
energy consumed by the lightening device of photobioreactors using red LED, the
spectral range of which is defined according to the action spectrum of
photosynthesis. This appears to be crucial information for applications in
which the energy must be rationalized, as it is the case for life support
systems in closed environments like a permanent spatial base or a submarine.
