FACS-based isolation of slowly growing cells: Double encapsulation of yeast in gel microdrops

Abstract

Isolating hyperproducing cells is important in biotechnology, but these cells usually grow slowly and can be overgrown by poorly producing cells. We describe a new method of isolating slowly growing cells from among rapidly growing cells, which has the potential for automation and high throughput (e.g., 100,000 cells/h). A model system is presented consisting of a mixed population of slowly growing mutant and rapidly growing wild-type yeast, which were encapsulated in double agarose gel microdrops (dGMDs); with most dGMDs initially containing single cells. Double encapsulation locates parent cells near dGMD centers, making microcolony measurement more accurate. After a 15-h incubation, fluorescent activated cell sorting was used to analyze and sort dGMDs with small microcolonies (slow growers) from dGMDs with large microcolonies (rapid growers). Successful isolation of slow growers from a mixed population of predominantly rapidly growing Saccharomyces cerevisiae cells was achieved.