response of the filamentous cyanobacterium Spirulina platensis to salt stress

In recent years, considerable interest has been expressed in the outdoor cultivation of Spirulina biomass for commercial purposes. In such cultures growing under arid and semi-arid conditions, a daily evaporation rate of 1-2 cm was measured, leading to a constant increase in the salt concentration. The responses of the filamentous cyanobacterium Spirulina platensis to increased NaCl concentrations (0.25-1.0 M) in addition to the concentration of sodium in the growth medium were studied. A two stage response to the salt stress was observed. This consisted of a short shock stage, followed by adaptation process. Upon exposure to high salt concentrations of 0.5 M and above, immediate inhibition of photosynthesis and respiration, and complete cessation of growth occurred. After a time lag, the energy-yielding processes exhibited restored activity. At 0.5 and 1.0 M NaCl photosynthesis reached 80% and 50% that of the control, while respiration was enhanced by 140 and 200%, respectively. The time lags were longer when the cells were exposed to higher NaCl concentrations. The resumption of growth and the establishment of new steady state growth rates were correlated to the recovery in respiration.