Under glucose abundant conditions (see Figure 1A), the following trends can be observed. Both the arcA and iclR knockout strains show an increased biomass yield. When combining see more these deletions (i.e. in ΔarcAΔiclR) the yield is further increased to 0.63 ± 0.01 c-mole/c-mole glucose, which approximates the theoretical biomass yield of 0.65 c-mole/c-mole glucose (assuming a P/O-ratio of 1.4) [28, 29]. The higher biomass yield is accompanied

by a 70 and 16% reduction in acetate and CO2, respectively. The results of the glucose limited cultures are shown in Figure 1B. The ΔarcAΔiclR strain exhibits an increased biomass yield compared to the wild type strain (0.52 ± 0.01 c-mole/c-mole vs. 0.46 ± 0.01 c-mole/c-mole), but the increment in biomass yield (i.e. 13%) is less distinct

as observed under glucose abundant conditions (47%). The increment in biomass yield is less pronounced under glucose limitation, because glucose limited cultures of the strain ΔarcAΔiclR show a decreased Selleckchem ARS-1620 biomass yield while the wild type shows an increased biomass yield compared to if these strains are cultivated under glucose abundant conditions. This can be easily explained: under glucose abundance, the wild type strain converts 16% of the carbon source to acetate as a result of overflow metabolism [30]. At a fixed, low growth rate and consequently under glucose limitation, the cell can easily cope with the delivered carbon and very little carbon is dissipated through formation

of byproducts. However, energy losses also occur in continuous cultures because of the existence of futile cycles [31]. In addition, as shown by Pirt and many others, an excessive fraction of the energy source is reserved for growth-independent maintenance, a factor which is relatively higher under glucose limitation [32–36]. For the wild type cultivated ALOX15 at a low growth rate (D = ±0.1 h -1), the absence of energy spilling by overflow metabolism compensates and even exceeds the energy spilling by futile cycling and the energy reserved for maintenance, explaining the higher biomass yield observed. In contrast, the ΔarcA ΔiclR strain does not show overflow metabolism under glucose abundance, and therefore the effects of energy loss by futile cycles and maintenance are more visible in this strain leading to a lower biomass yield under glucose limitation. For all experiments in which significantly higher biomass yields were observed, i.e. for ΔiclR in glucose abundant conditions and for ΔarcAΔiclR in glucose abundant and limiting conditions, the high yield is linked to a reduction in CO2 yield.