FIG. 6.

Regulatory mutations that reduce zwf expression increase the growth rate of Caulobacter. (A) SNP5 is located 7 bp upstream of the zwf transcriptional start site in isolate NA1000 (Crosson₁). An independently evolved allele (SNP5b) in NA1000 (Smit) is located 3 bp downstream of the zwf transcriptional start. (B) Both NA1000 promoters show reduced activity relative to those of CB15, as measured using transcriptional fusions to lacZ (one-way analysis of variance; P < 0.0001). (C) Model of carbon flux in CB15 cells (white arrows) and NA1000 cells (black arrows). Glucose (G) is phosphorylated to glucose-6-phosphate (G6P), which serves as the primary substrate for three metabolic pathways in Caulobacter. G6P can enter either the pentose phosphate (PP) or the Entner-Doudoroff (ED) pathway following dehydrogenation by the gene product of zwf, glucose-6-phosphate 1-dehydrogenase. Alternatively, G6P can be isomerized to fructose-6-phosphate (F6P) by glucose-6-phosphate isomerase. As dehydrogenation of G6P is the rate-limiting step in both the PP and ED pathways, reduced zwf expression is known to increase the amount of G6P available for isomerization into F6P and, consequently, increase the concentration of substrates used for cell membrane and cell wall biogenesis (29).