Cells were passaged every 3 7 days by passaging 1 : 3 to 1 : 6 to maintain culture densities between 30 and 80% confluent.
During continuous PBR operation, it is necessary to periodically remove algae to control culture density to minimize self-shading and maintain culture health.
An infrared sensor measures the amount of light absorbed by the culture and feeds the measurement to a proportional-integral feedback controller implemented on a microcontroller, which computes the necessary dilution rate to maintain a given culture density.
To measure the instantaneous growth rate, we made use of the fact that when culture density is maintained constant inside the turbidostat, the supply rate of the influx pump is directly proportional to the growth rate (Fig. 4b and see the 'Methods' section).
The culture density of the spheroid bodies was maintained at 10 20 cells/cm2 to prevent self aggregation.
The medium was added to the suspension cell culture to maintain a density of 2 6 × 10 cells/ml.
All species were maintained at culture densities between 1 × 105 and 1 × 107 cells/ml by repeated subculture, culture density was measured with a CASY model TT cell counter (Roche Diagnostics, Burgess Hill, UK).
Parasites were counted every 24 hr using a Coulter Counter (Beckman Coulter, Brea, CA), and cultures were diluted to maintain cell density between 10 and 2 × 10 cells/ml.
Parasites from stationary-phase culture were sub-cultured to maintain an average density of 2×106 cells/ml [29].
Cultures were split in two to maintain cell density below 1 × 10/mL.
