Black boxes refer to metabolites that were found to change significantly … As shown in Figure 3, alterations in metabolic profiles are essentially associated with amino and fatty acids biosynthetic pathways and, in most cases, are more evident at lower dilution rates. For instance, the profiles of octadecanoate (ocdca), tetradecanoate (ttdca), pentadecanoate (pdca) and 10,13-dimethyltetradecanoate (1013mlt) showed weak Inhibitors,research,lifescience,medical correlations when decreasing the dilution rate (from 0.1 to 0.05 h−1). Similarly, metabolites like succinate (succ), threonine (thr) and lactate

(lac) showed opposite patterns CP-690550 purchase compared to other metabolite profiles of E. coli ΔrelA mutant cultures. The succinate (succ) profile was the most divergent, showing clear differences between E. coli cultures at lower and higher dilutions rates. 4. Discussion The growth rate-dependent regulation of the metabolism Inhibitors,research,lifescience,medical is fundamental to fine-tune the fueling and biosynthetic reactions in such a way that cells can rapidly adapt to the existing environmental conditions. Typically, the cellular metabolism increases with the growth rate to promote

biomass formation Inhibitors,research,lifescience,medical in a more efficient way, as demonstrated by biomass yields in chemostat cultures (Table 1), i.e., increased biomass yields were observed at higher dilution rates. However, it has been shown that at reduced dilution rates (e.g., 0.05 and 0.1 h−1), metabolism is not directly related to the growth rate, as cell growth becomes limited by cell-carbon supply [1]. As a result, the non-linearity observed in most metabolic profiles (Figure 2) must Inhibitors,research,lifescience,medical be an effect of the selected growth conditions that are inherently dependent on the energy-efficient use of the carbon substrate for biomass production. In this study, the majority of intracellular metabolite levels had a maximum at a dilution Inhibitors,research,lifescience,medical rate of 0.1 h−1, decreasing below and above this dilution rate. This was previously suggested

to be associated with the extremely low residual glucose concentrations in glucose-limited cultures that triggers a series of cellular responses to adapt growth to these nutritional conditions [1,23]. According to Nanchen et al. [24], at a dilution rate of 0.1 h−1, large flux variations are verified in the metabolic network, in particular at the oxaloacetate node where two anaplerotic next reactions converge. The carbon flux through the glyoxylate cycle (i.e., an anaplerotic pathway that converts isocitrate to succinate or to malate via glyoxylate) is maximum at this dilution rate and decreases at higher dilution rates [1,25,26]. It was proposed [24,26,27] that at nutrient starvation conditions the cAMP-mediated catabolite repression of enzymes in the glyoxylate cycle is limited and the activity of the competing enzyme, i.e., the isocitrate dehydrogenase, is decreased. As such, it is believed that anaplerotic reactions are stimulated in hungry E.