EFFECT OF THE GROWTH-MEDIUM ON THE CELLULAR FATTY-ACID COMPOSITION OFAEROMONADS - CONSEQUENCES FOR THE CHEMOTAXONOMIC DIFFERENTIATION OF DNA HYBRIDIZATION GROUPS IN THE GENUS AEROMONAS

A total of 30 genotypically-characterized Aeromonas strains, encompass ing DNA hybridization groups (HGs) 1, 2, 3 (A. hydrophila), 4, 5A (A. caviae), and 8 (A. veronii biogroup sobria), were cultivated on two di fferent media, nutrient-rich trypticase soy agar (TSA) and nutrient-po or R2A medium, and their fatty acid methyl esters (FAMEs) were analyze d using an automated gas-liquid chromatographic system. A comparison o f the respective HG-specific FAME compositions revealed that the diffe rence in nutritional value of both media induced a pronounced quantita tive effect on the overall branched-chain fatty acid (BFA) content. St rains grown on TSA medium generally produced significant amounts of th e BFAs 13:0 iso, 15:0 iso, 15:0 iso 3OH. iso 17:1 omega 9c, and 17:0 i so, whereas these BFAs were detected in much lower concentrations or e ven were absent in R2A cultures. To compensate for this depletion, str ains cultivated on R2A agar produced higher amounts of the major fatty acids 16:1 omega 7c and 16:0. The consequences of the observed medium -dependent shift in fatty acid production for the chemotaxonomic diffe rentiation of HGs in Aeromonas were determined by constructing a simil arity matrix from the mean FAME library entries and by multivariate gr ouping via principal components analysis. Results obtained from both m athematical approaches clearly demonstrated a higher resolving power o f the TSA medium for the distinction of the six Aeromonas HGs examined in this study. In conclusion, when a standardized FAME protocol needs to be designed for taxonomic purposes, we recommend a thorough evalua tion of the influence of the growth medium on bacterial fatty acid com position. (C) 1997 Elsevier Science B.V.