Clearly, depending on culture conditions, metabolic flux distributions can differ considerably, reflecting the variable efficiency of carbon utilization either for biomass formation or starvation responses. Besides the aforementioned activities, a general increase in the central metabolism seems to occur at a dilution rate of 0.1 h−1, at which most metabolites reached its maximum levels. It is generally Inhibitors,research,lifescience,medical accepted that under steady state conditions

an increase in metabolite levels would correspond to an increase in metabolic activities, since metabolism is fully balanced and no accumulation of intracellular metabolites is expected to occur due to a tight coupling of the anabolism and catabolism [29,30]. In this work, metabolic profiles of chemostat cultures of two E. coli TGF-beta inhibitor strains (W3110 and the isogenic ΔrelA mutant) were determined by GC-MS analysis to explore

the effects of different growth rate conditions on the E. coli metabolism, as well as to verify the involvement of RelA under such conditions. It has been proposed that under low growth, Inhibitors,research,lifescience,medical the RelA-dependent stringent control of many cellular activities is promoted, including some key metabolic activities [8,31,32,33,34,35]. Yet, little is known about the RelA-dependent ppGpp control over the E. coli metabolism and its influence on central metabolic activities. Our results show that metabolite pools were strongly affected by the relA gene mutation as well as by the dilution Inhibitors,research,lifescience,medical rate. Though it was expected that metabolite levels would be altered with the dilution rate, due to the capacity of cells to alter their metabolism to cope with new growth conditions, the effect of the introduction of the single gene mutation (ΔrelA) was more difficult to predict. Inhibitors,research,lifescience,medical Differences observed in biomass yields have originally pointed to distinct metabolic behaviors between the two strains, i.e., biomass yields were higher in the ΔrelA mutant cultures and were not linearly-dependent Inhibitors,research,lifescience,medical on the growth rate at lower dilution rates (0.05 and 0.1 h−1). Additionally, metabolomics analysis revealed that approximately 50% of the whole

set of metabolites detected in this study presented significant changes between the E. coli W3110 and the ΔrelA mutant cultures (Figure 1). Most of these differences consisted in altered levels of amino acids and fatty acids indicating Ketanserin that the RelA-dependent ppGpp control of metabolic activities involving these metabolites might be affected. This seems to be the case of fatty acids like octadecanoate (ocdca), tetradecanoate (ttdca), pentadecanoate (pdca) and 10,13-dimethyltetradecanoate (1013mlt), that presented maximum levels at a dilution rate of 0.05 h−1 in the E. coli W3110 culture. Other examples include metabolites that were uniquely detected in the E. coli W3110 culture at a dilution rate of 0.1 h−1: N-acetyl-L-glutamate (acglu), lysine (lys), malate (mal), alpha-ketoglutarate (akg), itaconate (itcon) and malonate (ma) (see Figure S1).