25th International Meeting on Organic Geochemistry IMOG 2011

P-441
Investigating relationships between OM and diatom frustules
and their implications in the export of organic carbon in the
ocean
Maxime Suroy 1 , Brivaëla Moriceau 2 , Madeleine Goutx 1
1 Laboratoire de Microbiologie, Géochimie et Ecologie Marines, Université de la Méditerranée, CNRS UMR
6117, Marseille, France, 2 Laboratoire des Sciences de l’Environnement Marin, CNRS, UMR 6539, Site du
technopôle Brest-Iroise, Plouzané, France (corresponding author:maxime.suroy@univmed.fr)
One of the major processes of the biological carbon
pump (BCP) is the colloquially known ―ballasting‖ that
involves the association of mineral ballast with sinking
particles. Those minerals increase the density of
particles and the settling velocity leading to a
temporary or permanent sequestration of carbon into
the deep ocean. Among those minerals, three have
important role in ballasting because of their
concentrations and their abundance. These minerals
are biogenic silica, calcium carbonate and lithogenic
silica. The weak relationships between organic carbon
and biogenic silica at 1800m depth have led many
authors to hypothesize a lowest carrying capacity for
the biogenic silica of frustules compared to the
calcium carbonate of coccoliths. To understand
relationships between phytoplanktonic organic matter
(OM) and silica, at first, we conducted a degradation
experiment of a Thalassiosira weissflogii culture.
During 21 days, we measured lipid classes, sugars,
biogenic (BSi) and dissolved silica (DSi), and) for
modelling relationships between OM and BSi under
two growth conditions. A model taking into account 2
phases of silica with different polymerization degrees
(M3) gave a better fit with the BSi dissolution and
could explain the shape of some sugars and lipids
degradation curves.
Fig1. BSi dissolution rate of a degradation experiment
of a diatom culture and 2 model curves with one
phase (M1) or two phase of BSi (M3).
In a second step, we developed a method to identify
lipids within frustules. Indeed, proteins and
carbohydrates have been extensively studied in
diatom frustules showing molecular bindings between
some molecular species and silica phases into the
frustule. Lipid content of frustules is far less
understood. (Kates and Volcani, 1968) [1]. More
recently, Tesson et al (2008) [2] using X-Ray
photoelectron spectroscopy and Soler et al (in review)
[3] using FTIR reported the presence of lipids within
the frustule. Though these methods use the same first
steps (a separation of the frustule and the protoplast
using differential centrifugation after a vigorous
sonication [1,4]), they cannot identify the OM at the
molecular level and especially lipids. The assessment
of OM quality embedded within the frustule requires
the dissolution of this frustule and, therefore,
denaturing conditions. Kröger et al (1997) [4] have
developed a method to isolate a new family of
proteins using hydrofluoric acid (HF) which dissolve
the frustule after isolation. We will present a
development of this method applied to lipid analysis
by GC/MS. and will discuss its ability to bring new
insight into the lipid content of the diatom frustule and
to decipher the role of the interactions between
organic carbon and biogenic silica in the BCP.
[1] M. Kates, B. E. Volcani, Zeitschrift
Pflanzenphysiol. 1968, 60, 19.
[2] B. Tesson, M. J. Genet, V. Fernandez, S. Degand,
P. G Rouxhet and V. Martin-Jézéquel. 2009.
ChemBioChem. 10: 2011–2024
[3] C. Soler, B. Moriceau, C. Amiel, M. Goutx, O.
Ragueneau, P. Claquin. In review.
[4] N. Kröger N. Kröger, G. Lehmann, R. Rachel, M.
Sumper. 1997. Eur.J. Biochem. 250, 99.
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