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. Author manuscript; available in PMC: 2020 Sep 25.
Published in final edited form as: Cell Syst. 2019 Sep 4;9(3):229–242.e4. doi: 10.1016/j.cels.2019.06.008

Figure 2. Investigating positive and negative microbial interaction networks using MINI-Drop.

Figure 2.

(a) Schematic of the expected network for a synthetic consortium composed of an RFP-labeled E. coli methionine auxotroph (EC Met-) and a GFP-labeled B. subtilis tryptophan auxotroph (BS Trp-) (Table S1, E1). (b) Fluorescence microscopy image of representative single-species (EC Met- or BS Trp-) or two-member droplets. (c) Categorical scatter plot showing the number of BS Trp- or EC Met- cells in each droplet. The black horizontal line represents the mean and the error bars denote bootstrapped 95% confidence intervals for the mean. Gray lines denote statistically significant difference in means based on the Mann-Whitney U test (n=87, p=1.5e-6, left and n=372, p=3.8e–26, right). (d) The inferred interaction network for the EC Met-, BS Trp-consortium. The edge width is proportional to the log2 ratio of the average cell count in the presence of a partner to the average cell count in single strain droplets. Node size is proportional to the average cell count of each strain in single strain droplets. (e) Schematic of the expected network of an E. coli community that exhibits a strong unidirectional negative interaction. A GFP-labeled strain (sender) expresses LuxI, a synthetase for the quorum-sensing signal C6 acyl homoserine lactone (AHL). AHL binds to the receptor LuxR in an RFP-labeled strain (receiver) and activates the expression of a toxin MazF, generating a strong negative interaction (Table S1, E2). (f) Fluorescence microscopy image of representative droplets containing the sender strain, receiver strain or community. (g) Categorical scatter plot of the number of sender or receiver cells in each droplet in the presence or absence of a partner. The black line represents the mean and the error bars denote bootstrapped 95% confidence intervals for the mean. Gray lines denote statistically significant differences in the means (n=1512, p=2.2e–4, left, n=421, p=3.8e–14, right). (h) The inferred interaction network for the quorum sensing regulated toxin consortium.