Flow cytometric isolation of growth rate mutants: a yeast model

A rapid flow cytometric method for the isolation of growth rate mutants was developed. The method involves single cell entrapment within small agarose beads, microcolony formation and flow cytometric scanning and sorting of the beads based on the size of the microcolony they contain. Slow- and fast-growing yeast cells could be differentiated based on the size of the microcolonies they form. The potential of this method was first verified in a model system where a minority of cells of a fast-growing yeast strain, Candida pseudotropicalis IP-315, was enriched >250-fold from an initial mixture with a slow-growing yeast, Saccharomyces cerevisiae 352-1C. Microcolony size was reliably monitored by light scatter or light absorption signals. In addition, several slow-growing mutants of C. pseudotropicalis were isolated from a UV mutagenized population. This method could be generally applicable to other colony-forming microorganisms such as bacteria.