This part includes the coding region of the Phosphate acetyltransferase gene of Synechocystis, which catalyzes the reaction converting Acetyl CoA to acetyl-phosphate in the biomass formation pathway of Synechocystis. Overexpressing this gene can be used to increase acetate production in Synechocystis PCC. 6803. in an acs mutant strain. We tested it in the acs mutant and compared its acetate expression against the stand-alone acs mutant.
The results depicted in figure 1 show that although acetate concentrations were higher in the pta strain compared to the acs mutant strain (again, all engineered pta and ack strains also had the acs KO background). Nevertheless, both the total yields and Qp's are higher for the acs mutant during the period that both strains grow. More than that, the pta strain has a lower growth rate than the acs mutant during this period, providing evidence that any non-growth coupled production strategy is ultimately out-competed during growth phases. We show that this statement holds even when the non-growth coupled strategy is implemented in a strain that already makes a product in a growth coupled fashion. The take-away here is that in order to stabilize non-growth coupled production strategies, you'd need a synthetic gene-circuits that conditionally activate production during non-growth period. In this case, a circuit activating pta under dark conditions only, i.e. when Synechocystis does not grow, would help improve production, as at that stage, it would not produce acetate otherwise via growth-coupled production.