Response of Spirulina platensis (= Arthrospira fusiformis) from Lake Chitu, Ethiopia, to salinity stress from sodium salts

Abstract

Spirulina platensis (=Arthrospira fusiformis) was isolated from Lake Chitu, a soda crater lake in the Ethiopian Rift Valley, where it formsa dense and almost unialgal population. Growth experiments were run in turbidostats under constant light, to assess growth response and tolerance to salinity, as well as to the component anions. Salinity was tested over the range 13–88 g L^-1 using additions of NaHCO3, NaCl or Na2SO4. A maximum specific growth rate (µ_max d^-1) of 2.14 was achieved at the lowest salinity, but quantum yield (Φ%) was highest between 33 to 51 g L^-1. Increasing salinity of the medium reduced the specific growth rate (µ) to a minimum of 0.33 d^-1, and Φ to < 0.5%. Growth response in terms of µ and Φ was best in HCO ^-₃ , less in Cl^-, and least in SO ^2-₄ series. Cultures showed obvious differences in cellular morphology, pigment, nitrogen and phosphorus contents in response to treatment with the different anions. Results indicate that the species has a wide range of tolerance to salinity from NaHCO3. Some degree of tolerance is also shown to high concentrations of Cl^- and SO ²₄ , but with an overall lower performance of cells in terms of growth rate, light utilization efficiency, and nutrient status to cells grown in high HCO ^-₃ concentrations and the same levels of salinity and light.