Unique odd-chain polyenoic phospholipid fatty acids present in chytrid fungi

Chytrid fungi are ubiquitous components of aquatic and terrestrial ecosystems yet they remain understudied. To investigate the use of phospholipid fatty acids as phenotypic characteristics in taxonomic studies and biomarkers for ecological studies, 18 chytrid fungi isolated from soil to freshwater samples were grown in defined media and their phospholipid fatty acid profile determined. Gas chromatographic/mass spectral analysis indicated the presence of fatty acids typically associated with fungi, such as 16:1(n-7), 16:0, 18:2(n-6), 18:3(n-3) 18:1(n-9), and 18:0, as well as, a number of odd-chain length fatty acids, including two polyunsaturated C-17 fatty acids. Conversion to their 3-pyridylcarbinol ester facilitated GC-MS determination of double-bond positions and these fatty acid were identified as 6,9-17:2 [17:2(n-8)] and 6,9,12-17:3 [17:3(n-5)]. To the best of our knowledge, this is the first report of polyunsaturated C-17 fatty acids isolated from the phospholipids of chytrid fungi. Cluster analysis of PLFA profiles showed sufficient correlation with chytrid phylogeny to warrant inclusion of lipid analysis in species descriptions and the presence of several phospholipid fatty acids of restricted phylogenetic distributions suggests their usefulness as biomarkers for ecological studies.