Yeast has been engineered for cost-effective organic acid production
through metabolic engineering and synthetic biology techniques. However,
cell growth assays in these processes were performed in bulk at the
population level, thus obscuring the dynamics of rare single cells
exhibiting beneficial traits. Here, we introduce the use of monodisperse
picolitre droplets as bioreactors to cultivate yeast at the single-cell
level. We investigated the effect of acid stress on growth and the
effect of potassium ions on propionic acid tolerance for single yeast
cells of different species, genotypes and phenotypes. The results showed
that the average growth of single yeast cells in microdroplets was
identical to those of yeast populations grown in bulk, and microdroplet
compartments do not significantly affect cell viability. This approach
offers the prospect of detecting cell-to-cell variations in growth and
physiology and is expected to be applied for the engineering of yeast to
produce value-added bioproducts.