Submitted to: Cost Workshop on Biocontrol Symbiosis
Publication Type: Proceedings
Publication Acceptance Date: 5/23/2003
Publication Date: 6/11/2003
Citation: Viragh, E., Fodor, E., Chitwood, D.J., Farkas, T., Fodor, A. 2003. The role of membranes, polyunsaturated fatty acids and sterols in the thermoadaptation of entomopathogenic nematode (steinernema) species. On-line website: htttp://www.cost850.ch/publications/20020404_debrecen/20020404_12.pdf Interpretive Summary: Insect-parasitic nematodes are microscopic worms that are potential alternatives to chemical insecticides. One problem with agricultural use of these nematodes is that they poorly survive cold or hot environments. Because the types of fats in the membranes of the nematodes affect the ability of the membranes to remain fluid when exposed to cold temperatures, the fats affect the survival of the nematodes when exposed to extreme temperatures. This review summarizes research performed in an ARS-Hungarian collaboration, in which scientists are attempting to modify nematode fats in order to improve their resistance to harsh environmental temperatures. The various kinds of fats in the membranes of nematodes from two different environments were compared, as was the fluidity of membranes prepared from nematodes grown at different temperatures. The results indicated that the strains generally modified their fats and membrane fluidities in the same manner when grown at warm temperatures. The cold-environment nematode species had a fat composition different from that of the warm-environment nematode species. These discoveries about insect-parasitic nematodes will be used by researchers and industrial microbiologists interested in developing cold- and heat-tolerant strains of nematodes for use in biological control of insects. The public will eventually benefit when this technology provides safe control of insect pests.
Technical Abstract: A series of investigations examined the chemical composition and specific biophysical parameters of phospholipids from numerous Steinernema isolates from different geographical origins. Interestingly, phospholipids of steinernematids of the long dauer phenotype contained higher proportions of saturated fatty acids and lower proportions of polyunsaturated acids than did phospholipids from S. carpocapsae and S. feltiae. When four nematode strains of different geographic origins belonging to S. feltiae and S. carpocasae were propagated at low and warm temperatures, the warm climate strains increased the proportion of eicosapentaenoic acid (EPA) more than the boreal ones. This result may indicate that membranes of strains inhabiting colder regions do not require as much EPA to maintain structural and functional integrity as do those from warmer areas when grown at lower temperature. In two different measures of membrane fluidity¿Fourier transform infrared spectroscopy and fluorescence depolarization¿membranes prepared from phospholipids form the boreal nematode S. feltiae VIJE (from Norway) were more fluid than those from S. feltiae IS6 (from Israel), regardless of the nematode culture temperature. The results indicate that the survival of entomopathogenic nematodes depends on the ability of membrane fluidity to adjust appropriately to changes in environmental temperature.