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 hco₃⁻ and no₃⁻ from nutrient delivery. the tds-stress threshold was about 10 g/l. whereas inorganic n and p limitations slowed the rate of inorganic c (ci) 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 hco₃⁻ increase (560 mg c/l as a threshold). impaired photosynthesis led to a cascade of reduced ci-uptake, ph decrease, hco₃⁻ accumulation, and hco₃⁻-associated stress. thus, long-term photobioreactor operation requires balancing the delivery rates of co₂, n, p, and other tds components to avoid general and ci-associated tds stresses.