To test initial phosphate uptake rates, all three strains were first propagated in Media A+, which has an initial phosphate concentration of 370µM. We observed no change in biomass density between PST+ and wild-type (Supp Fig ), but, surprisingly, pitA overexpression increased final biomass density from 4.2 g/L to 5.5 g/L. Phosphate was depleted in all 3 strains within 48 hours, with a majority of uptake occurring in the first 24 hours. Due to the rapid phosphate uptake, differences between the three strains could not be observed. To look for changes in phosphate uptake rate, initial phosphate concentration was increased to 6mM by addition of KH2PO4. In these conditions, pstSCAB overexpression significantly reduced biomass density as measured by optical density (Figure ). Overexpression of pitA, however, increased growth similarly to the 370µM condition, though not significantly. Phosphate depletion occurs faster in PST+ over wild-type, with significantly lower residual phosphate levels at 24 hours and complete phosphate depletion within 72 hours (Figure ). Overexpression of pitA caused an unexpected decrease in phosphate accumulation in these conditions, from ~1.4mM residual P in the control to ~2.3mM in the pitA overexpression mutant. These results highlighted pstSCAB as the better phosphate transporter in these conditions, and so we chose the strain PST+ for further optimization.