http://www.biofilm.montana.edu/resources/theses/.html-3
"The algae produce O2 and soluble organic carbon and consume CO2. Their energy source is sunlight.
Bacteria consume the algal products and produce CO2 for the algae. The exchange of these products takes place within the film.
The kinetics of these aggregates are not describable with traditional models for algal processes which only predict growth in pure culture, and not organic product formation rate. However, this rate is necessary to describe the interaction and the growth of both algae and bacteria.
Algal cells build their carbon skeleton with organic carbon formed from CO2 using light energy. The enzyme ribulose diphosphate (RuBisCO) controls the first step of carbon fixation. RuBisCo has two unique properties: its molecular weight is over 500,000 and it has an active site for both O2 and CO2. The reaction with water and CO2 (the substrate) yields two phosphoglycerates, one for carbon fixation and one that goes into the Calvin cycle. With O2 as the substrate, the reaction yields one phosphoglycerate that goes into the Calvin cycle and one phosphoglycolate that is released from the cell. Glycolate has recently been identified as a major algal product. The reaction rate of RuBisCO-CO2 and RuBisCO-O2 is controlled by a competitive inhibition of CO2 versus O2. Thus the ratio of [CO2]/[O2] is an important factor influencing the rate of fixation versus the rate of organic carbon release.
Once the rates of carbon fixation and carbon release have been determined, the growth rate of the algal biomass can be predicted.
Traditional kinetic expressions can then predict bacterial growth and respiration (CO2) rate. The resulting integrated model can be used to predict the kinetics of algal-bacterial aggregates".