FIG 6.

Synechocystis sp. wild-type and ΔcphA mutant cells starved of nitrogen for 9 days and resuscitated under continuous light on BG-11 agar plates supplying fluctuating or limiting nitrogen levels. Chlorotic cultures were adjusted to an OD₇₅₀ of 1.0 and diluted in series. To enable fluctuating nitrogen supplementation, each cell suspension was dropped onto a transfer membrane, which was periodically moved to another plate containing a different nitrogen concentration. Photos were taken starting after 2 days of cultivation. Assays were performed using three biological replicates per strain. (A) Cells were exposed to 17.3 mM nitrate for 6 h per day and to no nitrogen for 18 h. (B) Cells were continuously exposed to a low concentration of nitrate (1.73 mM); to avoid nitrogen starvation, the transfer membrane was moved daily to a fresh plate containing 1.73 mM nitrate. (C) Both nitrogen limitation and fluctuating nitrogen availability were combined by exposing the cells to 1.73 mM nitrate for 4 h per day.