Comparative study of UV and visible light induced degradation of lipids in non-axenic senescent cells of Emiliania huxleyi
Résumé
Irradiation of killed non-axenic cells of Emiliania huxleyi (Prymnesiophyceae) by PAR and UVR resulted in a strong photodegradation of most of the unsaturated lipid components (chlorophylls, unsaturated fatty acids and brassicasterol) of this haptophyte. This degradation, which mainly involves type II (i.e. singlet oxygen-mediated) photosensitized oxidation processes, was induced by both PAR and UVR. Alkenones were the sole unsaturated components of E. huxleyi unaffected by photodegradation processes. This particular recalcitrance was attributed to the trans configuration of their double bonds, which is less reactive toward singlet oxygen than the classical cis configuration of the double bonds of the other lipids. UVR exposure also induced photosensitized stereomutation (cis-trans isomerization) of the double bonds of some lipids (e.g. monounsaturated fatty acids and chlorophyll phytyl side-chain) and of some of their oxidation products affording (after reduction) some compounds (e.g. 9-hydroxyoctadec-cis-10-enoic and 10-hydroxyoctadec-cis-8-enoic acids arising from oleic acid oxidation and 11-hydroxyoctadec-cis-12-enoic and 12-hydroxyoctadec-cis-10-enoic acids arising from cis-vaccenic acid oxidation) sufficiently specific to act as tracers of UVR-induced photodegradation in situ. A strong photodegradation of specific bacterial monounsaturated fatty acids (e.g. cis-vaccenic and 11-MeC18:1 omega 12 acids) was also observed and attributed to the migration of singlet oxygen from phytodetritus to the attached heterotrophic bacteria. (C) 2010 Elsevier B.V. All rights reserved.
Mots clés
LONG-CHAIN ALKENES
INDUCED DNA-DAMAGE
PHYTYL SIDE-CHAIN
DEPENDENT DEGRADATION
PHYTOPLANKTONIC CELLS
MARINE-ENVIRONMENT
SINGLET OXYGEN
FATTY-ACIDS
PAR
UVR
Photodegradation
Lipids
Senescent phytoplanktonic cells
Emiliania huxleyi
Alkenones
Attached heterotrophic bacteria
NORTHWESTERN MEDITERRANEAN SEA
FREE-RADICAL OXIDATION