Kinetics and Energetics of Photosynthetic Micro-Organisms in Photobioreactors
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inhibited by light [-7, 18]. This is a crucial difference compared to eucaryotic
micro-organisms with chloroplasts for which all macromolecules are obtained
from the Calvin cycle.
Interestingly, the photorespiration is cyanobacteria seems quasi inexistant
[-19-22] and has never been demonstrated in S. platensis. Also, special attention
must be paid to the incomplete Krebs cycle in the metabolism of eyanobacteria,
resulting in the amino acid synthesis via the glyoxylic shunt pathway.
2.3.3 Nitrogen Uptake
The preferred nitrogen source for S. platensis is the nitrate ion NO3, which enters
the cells by active transport. The nitrate is then reduced to ammonium NH +
consuming 4 (NADPH, H +) and is incorporated on glutamic acid in the amino acid
metabolism. Depending on the strains, NH + may also be used as nitrogen source.
2.3.4 Respiration
In darkness, the intracellular carbon reserves are consumed for maintenance of
cells [23]. For S. platensis, this is essentially sulfated glycogen [6] and polyhydroxybutyrate [8]. Respiration uses the same electron transport chains as photosynthesis in thylakoids and plasmic membrane [17]. Thus, the respiration is
totally inhibited by light in S. platensis when the dissipated light level is greater
than 5 W.m -2 [-7].
2.4 Stoichiometry of Growth
The above metabolic pathways analysis [24-27] enables determination of the
molar quantities of ATP and reduced cofactors (NADPH, H +) required for the
synthesis of a given metabolite. When the detailed composition of each class of
macromolecules is known (e.g. the aminogram for the Spirulina proteins [4, 5]),
biochemically structured stoichiomeric equations can be established. This approach [1] is an interesting alternative to the classical unstructured single
stoichiometric equation model for growth with fixed conversion yields for
substrates and products, only valid for limited applications. It enables allowances to be made for modifications in biomass composition and conversion
yields when different limiting conditions for growth are applied, by calculating
the production rates for each biomass compound defined above [28].
2.4.1 Synthesis of Cell Material
From the general analysis of S. platensis metabolism pathways, the stoichiometric equations including ATP and cofactor balances for synthesis of the main
169
inhibited by light [-7, 18]. This is a crucial difference compared to eucaryotic
micro-organisms with chloroplasts for which all macromolecules are obtained
from the Calvin cycle.
Interestingly, the photorespiration is cyanobacteria seems quasi inexistant
[-19-22] and has never been demonstrated in S. platensis. Also, special attention
must be paid to the incomplete Krebs cycle in the metabolism of eyanobacteria,
resulting in the amino acid synthesis via the glyoxylic shunt pathway.
2.3.3 Nitrogen Uptake
The preferred nitrogen source for S. platensis is the nitrate ion NO3, which enters
the cells by active transport. The nitrate is then reduced to ammonium NH +
consuming 4 (NADPH, H +) and is incorporated on glutamic acid in the amino acid
metabolism. Depending on the strains, NH + may also be used as nitrogen source.
2.3.4 Respiration
In darkness, the intracellular carbon reserves are consumed for maintenance of
cells [23]. For S. platensis, this is essentially sulfated glycogen [6] and polyhydroxybutyrate [8]. Respiration uses the same electron transport chains as photosynthesis in thylakoids and plasmic membrane [17]. Thus, the respiration is
totally inhibited by light in S. platensis when the dissipated light level is greater
than 5 W.m -2 [-7].
2.4 Stoichiometry of Growth
The above metabolic pathways analysis [24-27] enables determination of the
molar quantities of ATP and reduced cofactors (NADPH, H +) required for the
synthesis of a given metabolite. When the detailed composition of each class of
macromolecules is known (e.g. the aminogram for the Spirulina proteins [4, 5]),
biochemically structured stoichiomeric equations can be established. This approach [1] is an interesting alternative to the classical unstructured single
stoichiometric equation model for growth with fixed conversion yields for
substrates and products, only valid for limited applications. It enables allowances to be made for modifications in biomass composition and conversion
yields when different limiting conditions for growth are applied, by calculating
the production rates for each biomass compound defined above [28].
2.4.1 Synthesis of Cell Material
From the general analysis of S. platensis metabolism pathways, the stoichiometric equations including ATP and cofactor balances for synthesis of the main