Fig. 3

Microbial interactions. Engineered consortia demonstrate un-engineered interactions that can be classified into two categories: negative effects that cyanobacteria have on heterotrophs (a) and positive effects heterotrophs have on cyanobacteria (e). B. subtilis 3610 (b), W303^Clump S. cerevisiae (c), and E. coli W ΔcscR (d) were co-cultured with various concentrations of S. elongatus and heterotroph CFU/mL were determined after 12 hours of cultivation in either light or dark. Ratios of CFU in light compared to CFU in dark are reported (b-d). Additional strains were tested in Additional file 1: Figure S4. P-values of two-tailed t-tests with Welch’s correction are denoted with asterisks: * 0.01 to 0.05, ** 0.001 to 0.01, *** 0.0001 to 0.001, **** <0.0001. Positive effects of heterotrophs on cyanobacteria (e) were observed in liquid (f), evidenced by the number of cyanobacteria cells measured in co-cultures relative to axenic controls after 48 hours in constant light. These co-cultures were inoculated with two orders of magnitude fewer cscB ⁺ S. elongatus (~1.7x10⁶cells/mL) than the co-cultures depicted in Fig. 2 (~1.7x10⁸cells/mL), and 1 mM IPTG was added to all cultures to induce sucrose export. Thick horizontal lines represent the average measurement for each condition while thin horizontal lines represent one standard deviation from the mean. Positive effects of heterotrophs on cyanobacteria in previous liquid batch experiments is summarized in Additional file 1: Figure S5. The influence of heterotrophs on cyanobacterial growth on solid media (g) was determined by plating a dilute lawn of cscB ⁺ S. elongatus on ^CoBBG-11 agar plates. The cyanobacterial lawn was overlaid with the specified strain in ten-fold serial dilutions of heterotroph and in constant light with or without IPTG