An issue that arose with high concentrations of phosphate in Media A was precipitation of calcium phosphate. In biological phosphorus removal systems, this property is utilized to recover phosphate from wastewater. However, this property makes accurate phosphate quantification difficult when looking for maximal phosphate uptake rate. We found that reducing calcium concentration in the media from 50mM to 10mM was sufficient to make precipitation undetectable (Supp Fig 5). We called this modified formulation Media C, and all subsequent experiments were performed using the modified formulation. In early fedbatch photobioreactor runs we observed an unexpected decrease in biomass after 72 hours of growth, ultimately leading to photobleaching of the culture (Supp Fig 4). To avoid this, we terminated runs at 72 hours of growth and harvested biomass for analysis. Summarized in Figure are the results of 3 independent fermentation runs each of wild-type and PST+. Growth, shown in Figure , is comparable between strains, with optical density (OD) increasing linearly up to 72 hours. Dry cell weight (DCW) also increases linearly, though we observed a consistent but non-significant trend of higher DCW in PST+, suggesting that the mass per cell may be increased. Residual phosphate in the growth media accumulates rapidly in wild-type, as native regulation shuts off phosphate import in high P conditions (Figure ). In PST+, residual phosphate accumulates slightly before being almost fully consumed, which is reflected in the total P in the biomass fraction (Figure ). PST+ accumulates significantly more phosphate compared to wild-type, primarily stored in the form of polyphosphate (Figure ). Together, these data show that PST+ can be grown to very high P content with an elevated P uptake rate that is uninhibited by extracellular phosphorus concentration.