Responses of Synechocystis sp. PCC 6803 to total dissolved solids in long-term continuous operation of a photobioreactor.

This study evaluated how Synechocystis sp. PCC 6803 responds to high total dissolved solids (TDS) associated with eliminating nutrient limitation during long-term operation of a photobioreactor. The unique feature is that the TDS were not dominated by Na(+) and Cl(-), as in seawater, but by HCO(3)(-) and NO(3)(-) from nutrient delivery. The TDS-stress threshold was about 10 g/L. Whereas inorganic N and P limitations slowed the rate of inorganic C (C(i)) uptake in the light, TDS stress was manifested most strongly as a substantial increase of endogenous respiration rate at night. Relief from TDS stress was incomplete when lowered pH led to a HCO(3)(-) increase (560 mgC/L as a threshold). Impaired photosynthesis led to a cascade of reduced C(i)-uptake, pH decrease, HCO(3)(-) accumulation, and HCO(3)(-)-associated stress. Thus, long-term photobioreactor operation requires balancing the delivery rates of CO(2), N, P, and other TDS components to avoid general and C(i)-associated TDS stresses.