Biomedical Engineering Reference
In-Depth Information
WT strain
Light Intensity
Heat
Dissipation
Heat
Dissipation
Metabolic
Metabolic
activity
activity
Strain with reduced antenna
Light Intensity
Heat
Dissipation
Heat
Dissipation
Metabolic
Metabolic
activity
activity
Fig. 2.3.
The limits of light distribution in photobioreactors yields. In photobiore-
actors, a high cell concentration should be maintained to obtain a reasonable yield.
This leads to unequal light distribution. In fact, more exposed cellular layers (
left
)
absorb a very high light, which can be used only partially for metabolism. A large
fraction is also dissipated thermally to avoid establishing oxidative stress in cells.
Internal layers (
right
) are illuminated by a very poor light, insu
cient to support
intense metabolic activity. If a strain with reduced antenna is used in the photo-
bioreactor, with an equal cellular concentration, the optical density of the culture is
lower and light is more e
ciently distributed. External cells absorb a lower propor-
tion of available light, which thus reaches more internal layers supporting metabolic
activity.
Among the different mechanisms, it is important to increase the capacity to
respond to fast alterations in light intensity.
The only strategy attempted so far to increase the light distribution in pho-
tobioreactors has been the use of mutants lacking all the antenna proteins, a
class of proteins that are responsible of a large fraction of light harvesting in
photosynthetic eukaryotes. With this approach, light distribution has been in-
deed improved. However, cells suffered for strong photo-sensitivity and did not
survive when exposed to full sunlight. This puzzling phenotype ( lower antenna
size is expected to decrease the number of photons funnelled to RCII-reaction
