The adaptation of fatty acid composition of Chromohalobacter israelensis, a euryhalophilic bacterium, grown at different salt concentrations was studied. C. israelensis tolerated NaCl up to concentrations of 20% (w/v) and showed optimal growth at 7% (w/v). Major fatty acids of this bacterium were palmitic acid (16:0), stearic acid (18:0), palmetoleic acid (16:1cisΔ9), and cis-vaccenic acid (18:1Δ11). The salt concentration strongly influenced the fatty acid composition. In the presence of sub-optimal salt concentrations, the degree of saturation decreased, suggesting the importance of salt in maintaining the osmotic balance of the cell with its environment.

Halophilic bacteria require the presence of high concentrations of NaCl for their survival. This group of bacteria also includes halotolerant bacteria which can tolerate a wide range of salt concentrations [9, 20]. Salt-tolerant bacteria can be divided into euryhaline and stenohaline. Euryhaline bacteria have no compulsory requirement for NaCl, whereas stenohaline bacteria have an absolute need of NaCl for growth [22]. The adaptation to varying salt concentrations forces the bacteria to develop specialized molecules and physiological mechanisms to cope with the above-mentioned environmental stress [19]. A change in NaCl concentrations involves corresponding changes in both osmotic pressure and the water activity of the suspending solution. In low salts a cell is faced with too much water and must prevent or slow down water influx, whereas in high salts the cells are water-poor and must prevent dehydration [15]. In each situation creation of a more hydrophobic membrane environment would be advantageous to the cells since it would create situations in which water movement would be thermodynamically unfavorable [21]. Bacteria that are exposed to low matrix water potentials may adjust membrane fatty acid composition or make other adaptations to offset the lipid-solidifying effects of dehydration in a fashion that is analogous to the homeoviscous adaptation of membrane fluidity to changes in temperature [10]. It has been reported that the total unsaturated fatty acid content decreases when the osmolality of the growth medium is increased [11].

The bacteria adjust to the varying water activity either by accumulating compatible solutes or by altering the fatty acid composition of the cytoplasmic membrane in order to assist in the maintenance of a bilayer configuration [14, 16, 17].

The present study investigated the effect of adaptation of the euryhalophilic bacterium Chromohalobacter israelensis to a wide range of salt concentrations (NaCl) on the level of the fatty acid composition of the cells.