Growth-mediated variations in fatty acids of Xenorhabdus sp.

Abstract

The bacterium Xenorhabdus sp. is symbiotically associated with the entomopathogenic nematode Steinernema riobravis. This nematode is produced in monoxenic culture with Xenorhabdus sp. and is sold as a biological insecticide. Acceptable yields in fermentors can only be achieved in the presence of vigorous growth of the bacterium. We investigated the fatty acid composition of Xenorhabdus species when grown at 15, 20, 25 or 30 degrees C on media containing one of two primary carbon sources: glucose or lipids from the insect host, Galleria mellonella. Both temperature and primary carbon source significantly affected lipid quantity and quality in Xenorhabdus sp. Bacteria grown with insect lipids as a primary carbon source accumulated more lipids with greater proportion of longer chain fatty acids than bacteria grown with glucose as a primary carbon source. Cells grown with insect lipids at 15 degrees C had a lower lipid content than cells grown on the same media at 20, 25 or 30 degrees C. Increasing growth temperature increased saturated fatty acids and decreased unsaturated fatty acids, irrespective of carbon source. We recommend addition of complex fatty acid sources that resemble natural host lipids to growth medium for mass producing entomopathogenic nematodes. This could provide nematode quality similar to in vivo-produced nematodes.