| The interest in the use of high-density algal cultures is increasing due to their recognized biotechnological potential. The applications include: the production of valuable pharmaceutical and genetically engineered products, decomposition of organic compounds in waste water, and development of life support systems. Two major issues associated with the use of high-density algal cultures are addressed in this research.;First, a photobioreactor system has been designed, constructed, and implemented to achieve high photosynthetic rates in high-density photoautotrophic algal-cell suspensions. This unit is designed for efficient production of oxygen and biomass, but can also be used for the production of secreted products. Special features of the design include: a specific illuminating surface-area of 3.2 cm;Second, results from the photobioreactor indicated the necessity of studying the cell-cycle kinetics of Chlorella vulgaris at high and low cell concentrations. The experimental work demonstrated that at high cell concentrations (;In the presence of these compounds Chlorella vulgaris exhibits asynchronous initiation of DNA replication. The asynchronicity increases the total time of the cell cycle by apparently halting the cycle after the first round of DNA replication, as cells with three nuclei are formed in these cultures. The cell-cycle alteration can be either temporary or permanent depending on the concentration of the compounds. These compounds can be secreted to the medium both in growth and stationary phases. Other means of growth inhibition such as nutrient starvation, light limitation, and presence of non-biogenic inhibitory compounds did not affect the cell cycle in the same way as biogenic compounds, and asynchronous division was not observed under those conditions. |
