Osmoregulation in the Extremely Euryhaline Marine Micro-Alga Chlorella autotrophica

Abstract

C. autotrophica (Clone 580) grows over the external salinity range of 1-400% artificial sea water (ASW), can photosynthesize over the range from 1-600% ASW and survives the complete evaporation of seawater. The alga grown at high salinities shows an increase in cell volume and a small decrease in cell water content. Measurements of ion content were made by neutron activation analysis on cells washed in isoosmotic sorbitol solutions which contained a few mM of major ions to prevent ion leakage. Cells grown at various ASW concentrations contain large quantities of Na, K and Cl ions. Measurements of cations associated with cell wall and intracellular macromolecules were made to determine intracellular concentration of free ions. The proline content of cells increases in response to increases in external salinity. Cells in 300% ASW contain 1500-1600 mM proline.