Effects Of Temperature And Dietary Lipids On Phospholipid Fatty Acids And Membrane Fluidity In SteInernema Carpocapsae 1

Journal of Nematology 26(3):278-285. 1994. © T h e Society of Nematologists 1994.

Effects of Temperature and Dietary Lipids on Phospholipid Fatty Acids and Membrane Fluidity in
Steinernema carpocapsae 1
A.
FODOR, 2

I. DE'~,3 T.

FARKAS, 3'4 AND

D. J.

CHITWOOD 5

Abstract: T h e phospholipid composition of Steinernema carpocapsae was studied in relation to diet and culturetemperature. W h e n reared at 18 and 27.5 C on Galleria mellonella or on an artificial diet supplemented with lard, 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 fatty acid composition of the diet. Because the level of linolenic acid (18:3(n - 3))in nematode phospholipids was very low and because eicosapentaenoic acid was present even when its precursor (linolenic acid) was undetectable in the diet, S. carpocapsae likely produces n - 3 polyunsaturated fatty acids by de novo biosynthesis, a pathway seldom reported in eukaryotic animals. Reduction of growth temperature from 25 to 18 C increased the proportion of 20:5(n - 3) but not otherpolyunsaturated 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 in the outermost region of the bilayer. Dietary fish oil increased fluidity in the outermost region but increased rigidity in deeper regions. Therefore, S. carpocapsae appears tomodify its membrane physical state in response to temperature, and eicosapentaenoic acid may be involved in this response. T h e results also indicate that nematode m e m b r a n e physical state can be modified dietarily, possibly to the benefit of host-finding or survival of S. carpocapsae at low temperatures. Key words: bacterium, diet, entomopathogenic nematode, fatty acid, fluidity, fluorescenceanisotropy, Galleria mellonella, insect, lipid, membrane, nematode, phospholipid, Steinernema carpocapsae, temperature, Xenorhabdus nematophilus.

Commercialization o f e n t o m o p a t h o genic n e m a t o d e s as biological control agents of insects would be accelerated by improvements in nematode persistence after field application and by increasing the shelf life o f products containingentomopathogenic nematodes (17). Little research, however, has focused upon the biochemical, biophysical and physiological mechanisms involved in the sensitivity of entomopathogenic nematodes to low humidity, extremes of temperature, or extended periods of storage. Based upon a recent examination of the lipid and fatty acid compositions of Steinernema spp. and Heterorhabditis spp. during storage,Selvan et al. (27,28) proposed that the higher telReceived for publication 10 May 1994. i Supported by Hungarian-U.S. Joint Science and Technology Program contract number JF 138/91. 2 Institute of Genetics, E6tv6s Lorand University, Muzeiim k6rfit 4/A, H-1088 Budapest, Hungary. s Institute of Biochemistry, Biological Research Center, Hungarian Academy of Sciences, H-6701 Szeged, Hungary. 4 Authorto whom correspondence should be addressed. 5 USDA ARS, Nematology Laboratory, Building 011A, BARC-West, Beltsville, MD 20705-2350. We thank Dr. Ramon Georgis of Biosys for supplying the nematode strains used in this investigation.

ative percentage of unsaturated fatty acids found in H. bacteriophora than in S. carpocapsae or S. glaseri resulted in poorer survival. The phylum Nematoda includesspecies that are among the most adaptive animals, surviving u n d e r very extreme environmental conditions. In any organism exposed to fluctuating environmental conditions, maintenance o f the functional integrity and p r o p e r physicochemical properties of biological membranes is a prerequisite for survival. Prevention of the bilayer to non-bilayer transition of membranes in desiccating...