S8: Flow cytometry controlled continous cultures for the rapid selection of desired strains

Continuous, automated sampling with a flow cytometer from a continuous bioreactor permits operation of the reactor in ‘cytostat’ mode in which the cell concentration is kept constant through a controlled feed pump.  Because flow cytometry detects and counts individual cells the cell density can be kept so low that cell growth in the reactor does not significantly alter the feed medium. Thus, cells are always exposed to a precisely defined growth medium that can be designed to enforce a precise, constant selection pressure on the growing cell population.  We have applied this approach to rapidly isolate Saccharomyces cerevisiae strains that are resistant to technologically adverse conditions. Such strains evolved from the wildtype cell population due to the natural mutation rate.  Or the mutation rate can be induced  in the inoculum culture.  The system is also ideal to rapidly isolate genes conferring desired phenotypes to cells from cell populations that have been transformed with specific gene libraries.