(680d) High-Throughput Screen of Extracellular Metabolites Using Microfluidics

Cellular metabolism is defined by the biochemical reactions taking place within the cell as well as the uptake and secretion of metabolites in the extracellular medium.  Combinatorial approaches for strain improvement aim to randomly modulate the metabolic profile within a population followed by selection of a clone with enhanced phenotype.  However, conventional methods for the high-throughput screening of cellular metabolism (e.g. FACS) are unable to retain the association between a particular clone and its extracellular metabolites.  In an industrial setting, the metabolites of interest are frequently extracellular (e.g. substrate or secreted product).  As such, the ability to screen populations based on their extracellular metabolism is highly desirable.

We have developed a high-throughput screening method based on the measurement of the extracellular metabolites of single cells.  Using microfluidics, we encapsulate single cells in the droplets of a water-in-oil emulsion.  The electromagnetic properties of these emulsions allow us to coalesce droplets containing cells with assay droplets and later sort the combined droplets based on the assay result.  We have demonstrated this technology for the measurement of glucose, xylose, and lactate, though other analytes are possible.  Sorting populations for xylose uptake has provided us with crucial insight regarding the metabolism of recombinant xylose-consuming Saccharomyces cerevisiae.  This platform can be extended to various cell types, as we have demonstrated with mammalian cells (Jurkat, clone E6-1).  In this latter context, lactate measurement may provide insight regarding cancer cell metabolism that would otherwise be difficult to access.  We have also shown the ability to distinguish between enantiomers, an important capability with regards to pharmaceutical production.   The broad range of detectable analytes and cells that can be cultured using this powerful approach promises to significantly enhance metabolic engineering efforts.