Fatty acid composition and dynamics of selected fungal-feeding nematodes and fungi

Fatty acid profiles of fungal-feeding nematodes, Aphelenchus avenae and Aph elenchoides composticola, and selected fungi were determined in microcosm c ultures of agar, broth, or sand amended with organic matter. Fatty acids of A. avenae and A. composticola included 16:0 18:0, 18:1 omega7, 18:1 omega9 , 18:2, 20:0, 20:1, 20:2, 20:3 and 20:4 phospholipid fatty acids (PLFAs) an d neutral lipid fatty acids (NLFAs). The nematodes differed in relative amo unts of saturated and C-18 fatty acids. Similar C-16 and C-18 PLFAs and who le-cell fatty acids were found in Rhizoctonia solani, Fusarium oxysporum an d Trichoderma sp. with 18:2 omega6 as the major component. The C-20 fatty a cids were not found in these fungi. Although only present in the nematodes, C-20 PLFAs were only detected when nematode population levels were greater than or equal to 22 per gram of sand, suggesting that there is a detection threshold that might limit their use as biomarkers in the soil community. After removal of nematodes from a food source, the relative amount Of C-20 PLFAs (structural components of nematode cell membranes) decreased more slo wly than the C-16 and C-18 PLFAs, which may have reflected ingested fungal cytoplasm in the nematode intestine. In the early stage of organic matter d ecomposition, total and fungal PLFAs were lower in the presence of A. compo sticola then in its absence at C:N ratios greater than or equal to 30:1. (C ) 2001 Elsevier Science Inc. All rights reserved.