Fig. 5. Droplet flow cytometry for cell-to-cell interaction. (A) Screening of bacteria inhibiting S. aureus growth using DE-FACS. (1) Target S. aureus cells with a GFP reporter were encapsulated with either antibiotic producer, S. venezuelae (secreting red fluorescent metabolites) or mate E. coli (with a far-red fluorescent reporter). (2) The inhibition of S. aureus with the growth of S. venezuelae, and the growth of both E. coli and S. aureus, which yielded different combinations of fluorescent signals. (3 and 4) Selection of DE droplets with the lowest fluorescence level caused the enrichment of killers S. venezuelae (3) rather than mates E. coli (4). Adapted with permission from ref. 32. Copyright 2017 National Academy of Sciences. (B) The workflow of high-throughput screening and selection of the co-culture of recombinant E. coli and S. aureus for antibiotic drug discovery via the integration of agarose droplets and FACS. (1) environmental DNA was subjected to a limited DNasel digestion, (2) metagenomic DNA was cloned and then transferred into E. coli, (3) individual recombinant E. coli were co-encapsulated with live S. aureus (small yellow spheres), (4) microdroplets were labelled with a fluorogenic viability probe and then selected by FACS to isolate E. coli secreting bacterial natural products. Adapted with permission from ref. 33. Copyright 2013 John Wiley & Sons, Inc.