Influence of changes in microbial cell membrane composition on isotopic fractionation of nitrate during denitrification

Abstract

Pure cultures of Thauera aromatica were stressed by the addition of the toxic solvents 1-octanol and 4-chlorophenol causing adaptive modifications in their cell-membrane fatty acid composition. At the same time, we investigated the isotopic fractionation in δ15N-NO3- during denitrification. We observed a change in the degree of saturation (DoS) of the bacteria as a reaction to solvent stress and a higher degree of saturation was directly correlated to the concentration of solvents in the cell membrane. The enrichment factor ε15N-NO3- during denitrification showed a linear dependency to the DoS as well as to the membrane solvent concentration. Denitrifying bacteria thus may express less negative ε15N-NO3- when they are exposed to environmental stress that changes their cell membrane composition.