EFFECTS OF TEMPERATURE AND DIETARY LIPIDS ON PHOSPHOLIPID FATTY-ACIDSAND MEMBRANE FLUIDITY IN STEINERNEMA-CARPOCAPSAE

The phospholipid composition of Steinernema carpocapsae was studied in relation to diet and culture temperature. When reared at 18 and 27.5 C on Galleria mellonella or on an artificial diet supplemented with la rd, linseed oil, or fish oil as lipid sources, nematode phospholipids contained an abundance of 20-carbon polyunsaturated fatty acids, with eicosapentaenoic acid (20:5(n - 3)) predominant, regardless of the fat ty acid composition of the diet. Because the level of linolenic acid ( 18:3(n - 3)) in nematode phospholipids was very low and because eicosa pentaenoic acid was present even when its precursor (linolenic acid) w as undetectable in the diet, S. carpocapsae likely produces n - 3 poly unsaturated fatty acids by de novo biosynthesis, a pathway seldom repo rted in eukaryotic animals. Reduction of growth temperature from 25 to 18 C increased the proportion of 20:5(n - 3) but not other polyunsatu rated fatty acids. A fluorescence polarization technique revealed that vesicles produced from phospholipids of nematodes reared at 18 C were less ordered than those from nematodes reared at 27.5 C, especially i n the outermost region of the bilayer. Dietary fish oil increased flui dity in the outermost region but increased rigidity in deeper regions. Therefore, S. carpocapsae appears to modify its membrane physical sta te in response to temperature, and eicosapentaenoic acid may be involv ed in this response. The results also indicate that nematode membrane physical state can be modified dietarily, possibly to the benefit of h ost-finding or survival of S. carpocapsae at low temperatures.