Flux map of TCA cycle and citrate lyase. During oxygen-limited growth on αKG maximal biomass will be made by utilizing the citrate lyase reaction. As oxygen becomes more limiting, the reactions shown in red, culminating in the production of oxaloacetate (OAA), were predicted by iJR904 to be used more heavily than the forward direction of the TCA cycle reactions (shown in black). iJE660a does not include the citrate lyase reaction so carbon flow is directed only in the forward direction of the TCA cycle; these reactions produce more reduced redox carriers, which are difficult for the cell to oxidize in an oxygen-limited environment. The '+' sign indicates that the cofactor is produced by the reaction in the direction shown and the '-' sign indicates that the cofactor is consumed. For abbreviations see Figure 5, with the following additions: ACCOA, acetyl-CoA; FUM, fumarate; MAL, malate, PYR, pyruvate.