196
J.-F. Cornet et al.
3.6 Dark Cycle: Respiration
Equation (38) enables one to calculate the decrease rate in Spirulina biomass by
respiration in the dark at 36 ~ which is equal to 9" 10-4 kg.kg biomass- 1.h- 1
This rate has been confirmed by experiments in bioreactors. It has been shown
that the micro-organism can be maintained for 24 h in darkness without the
growth rate in the light being subsequently impaired [7]. Equation (38) can then
be used if Spirulina is cultivated under dark cycle conditions.
4 Growth Kinetics Under Mineral Limitations
4.1 Physiological Effects of Nitrogen, Sulphur and Phosphorus
Mineral Limitations on Spirulina Growth
4.1.1 Nitrate Limitation
Initial studies on the cyanobacterium Anacystis nidulans [74] showed that
during nitrate depletion, growth stops, apoproteins of phycocyanins are degraded without significant changes in chlorophyll [75, 76] and carotenoid, and
intracellular glycogen concomitantly accumulates E77]. Re-addition of nitrates
to deficient cultures reverses these trends. These observations were confirmed in
Synechocystis [78] and Agmenellum quadruplicatum [79]. Allen et al. [80]
recently suggested that some inactivation of photosystem II could result in
a decrease in photosynthesis efficiency.
The cyanobacterium Spirulina seems to follow this general response to
nitrogen deprivation E81] though carbohydrate accumulation has not been
extensively studied. Little information is available on intracellular glycogen [-6]
and exocellular polysaccharides [9], which are both sulfated.
Figure 10 shows a batch culture performed in a rectangular photoreactor
with nitrate limitation. Growth and accumulation of major cell components in
the presence of nitrates are initially exponential and rapidly become linear when
light limitation is introduced by increasing shadowing. As soon as nitrates are
exhausted, total amounts of proteins and chlorophyll a in the culture stabilize to
steady-state levels. As expected, phycocyanins begin to be degraded and are
used as a nitrogen reserve for the continued synthesis of other proteins, the
amount of total proteins remaining constant. Intense synthesis of intracellular
sulfated glycogen [6,77-80] results in a marked accumulation of residual
biomass. This intracellular glycogen accumulation is accompanied by an abundant excretion of sulfated exopolysaccharide.
Nitrate replenishment induces a rapid restoration of high levels of total
proteins, which originates in a very strong and rapid increase of phycocyanins,
J.-F. Cornet et al.
3.6 Dark Cycle: Respiration
Equation (38) enables one to calculate the decrease rate in Spirulina biomass by
respiration in the dark at 36 ~ which is equal to 9" 10-4 kg.kg biomass- 1.h- 1
This rate has been confirmed by experiments in bioreactors. It has been shown
that the micro-organism can be maintained for 24 h in darkness without the
growth rate in the light being subsequently impaired [7]. Equation (38) can then
be used if Spirulina is cultivated under dark cycle conditions.
4 Growth Kinetics Under Mineral Limitations
4.1 Physiological Effects of Nitrogen, Sulphur and Phosphorus
Mineral Limitations on Spirulina Growth
4.1.1 Nitrate Limitation
Initial studies on the cyanobacterium Anacystis nidulans [74] showed that
during nitrate depletion, growth stops, apoproteins of phycocyanins are degraded without significant changes in chlorophyll [75, 76] and carotenoid, and
intracellular glycogen concomitantly accumulates E77]. Re-addition of nitrates
to deficient cultures reverses these trends. These observations were confirmed in
Synechocystis [78] and Agmenellum quadruplicatum [79]. Allen et al. [80]
recently suggested that some inactivation of photosystem II could result in
a decrease in photosynthesis efficiency.
The cyanobacterium Spirulina seems to follow this general response to
nitrogen deprivation E81] though carbohydrate accumulation has not been
extensively studied. Little information is available on intracellular glycogen [-6]
and exocellular polysaccharides [9], which are both sulfated.
Figure 10 shows a batch culture performed in a rectangular photoreactor
with nitrate limitation. Growth and accumulation of major cell components in
the presence of nitrates are initially exponential and rapidly become linear when
light limitation is introduced by increasing shadowing. As soon as nitrates are
exhausted, total amounts of proteins and chlorophyll a in the culture stabilize to
steady-state levels. As expected, phycocyanins begin to be degraded and are
used as a nitrogen reserve for the continued synthesis of other proteins, the
amount of total proteins remaining constant. Intense synthesis of intracellular
sulfated glycogen [6,77-80] results in a marked accumulation of residual
biomass. This intracellular glycogen accumulation is accompanied by an abundant excretion of sulfated exopolysaccharide.
Nitrate replenishment induces a rapid restoration of high levels of total
proteins, which originates in a very strong and rapid increase of phycocyanins,