THE ADAPTATION OF DUNALIELLA TO WIDELY-DIFFERING SALT CONCENTRATIONS

Methods are described for adapting pure cell-lines of Dunaliella, a green unicellular alga, to grow at concentrations between 0.5 M and 3.5 M NaCl. It is shown that, provided large abrupt changes are avoided, cells of the same cell-line can become adapted to grow over this wide range of salt concentration. Once adapted, cultures are able to continue growing at a steady rate for many generations provided that the salt concentration remains constant. Viability tests performed after abrupt changes in salt concentration have shown that survival is higher after downward than after upward changes (3.5 M to 0.5 M NaCl: 20%; 0.5 M to 3.5 M NaCl: 0.01% in D. parva 19/9). When the change in concentration from 0.5 M to 3.5 M NaCl takes place over a period of 48 h viability approaches 100%. The time needed for 100% survival for a downward change over the same range is only 1.5 h. There is no evidence for a genetic difference between cell-lines adapted to particular concentrations of salt and it is concluded that the so-called 'halophilic' and 'halotolerant' strains are interchangeable. It seems likely that the difference between the two types is a matter of gene expression. © 1990 Oxford University Press.