Liquid media development for Heterorhabditis bacteriophora: lipid source and concentration

Lipids are important entomopathogenic nematode nutritional components becau se they are energy reserves and serve as indicators of nematode quality. Th e composition and concentration of the media lipid component determine bact erial and nematode yields. Heterorhabditis bacteriophora and its symbiont, Photorhabdus luminescens, were cultured in media containing various lipid s ources. As lipid concentration increased from 2.5% to 8.0% (w/v), the final yield and productivity [calculated from the number of infective juveniles (IJ)] increased significantly from 2.1 x 10(5) IJ ml(-1) to 2.8 x 10(5) IJ ml(-1) (P < 0.05) and from 8.9 x 10(5) IJ l(-1) day(-1) to 11.8 x 10(5) IJ l(-1) day(-1) (P < 0.05), respectively. The nematode yield coefficient (IJ per gram of media), however, decreased from 2.8 x 10(6) to 2.2 x 10(6) (P< 0.05), while recovery increased from 45.3% to 58.0% (P < 0.05). Bacterial c ell mass remained constant at 4.6 mg ml(-1) with changing lipid content (P > 0.05). The largest nematode yield (2.8 x 105 IJ ml(-1)) was achieved with in 8 days, using a medium containing an 8% (w/v) olive and canola oil (50:5 0 w/v) combination. Moreover, developmental synchrony was achieved in this medium with 96% infective juveniles. In short, lipid sources rich in mono-u nsaturated fatty acids and poor in saturated fatty acids produced optimal n ematode growth.