Fig. 2. SpoTH gene activation increases growth rate.

a P_GFP_SpoTH plasmid used to activate the SpoTH gene via the inducible pTet promoter. b Circuit describing how SpoTH induction via aTc affects ribosomes and growth rate. Addition of aTc increases SpoTH concentration, which lowers ppGpp concentration and consequently upregulates both free ribosome concentration and growth rate³⁵. The dashed flat headed arrow from SpoTH to ribosomes represents the load that SpoTH expression places on ribosomes as SpoTH’s mRNA is translated. c The growth rate as SpoTH is increased in the wild-type MG1655, CF944, CF945, and CF946 strains³⁵ growing in glycerol as the sole carbon source. d Growth rate normalized by the growth rate at aTc = 0 nM, as SpoTH is expressed in CF945 growing in lactose, glycerol, fructose, or glucose as the sole carbon source. The maximum normalized growth rate for each carbon source is marked by open squares. e The maximum normalized growth rate versus the growth rate at aTc = 0 nM for each carbon source. Data are shown as the mean ± one standard deviation (N = 4, two biological replicates each with two technical replicates). Individual experimental values are presented as gray dots. The complete experimental protocol is provided in the Materials and Methods section. Plasmid description, plasmid map, and essential DNA sequences are provided in Supplementary Information section Plasmid maps and DNA sequences.