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

Anja Wunderlich,Martin Elsner,Hermann J Heipieper,Florian Einsiedl,O Chudaev,Y Kharaka,O Shouakar-Stash,R Harmon,R Millot

doi:10.1051/e3sconf/20199801051

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.

Highlights

Isotope enrichment factors ε15N and ε18O of nitrate during denitrification are used to determine the presence of this process in anoxic environments
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
A positive linear relationship was observed between the calculated membrane concentration MMC of solvent in the cell and the calculated DoS of the cell membrane fatty acids

Summary

Introduction

Isotope enrichment factors ε15N and ε18O of nitrate during denitrification are used to determine the presence of this process in anoxic environments. More detailed knowledge of the enrichment factors under environmental conditions could be used to quantify denitrification or to model processes like coupled denitrification with anammox or other processes affecting nitrate pools in the water. Enrichment factors for both isotopes have been found to vary greatly in laboratory and field experiments. We found that the presence of bacteria with a NXR nitrate reductase enzyme can foster an isotope exchange of 18O -NO3- with the oxygen atoms in water, under anoxic conditions providing one possible explanation for the varied ε18O-NO3- values observed during denitrification, the difference between field observations and laboratory experiments [1].

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Conclusion