Methodology
Tracking marine lipid degradation trends
by latroscan analyses and by molecular
composition of fatty acids
L. Méjanelle, L. Pinturier-Geiss, J. Laureillard, A. Saliot
Université de Paris 6, laboratoire de physique et chimie marines, case 134, 4 place Jussieu,
75252 Paris Cedex 05, France - mejanel@ccr.jussieu.fr
Bacteria play a key role in the recycling of particulate organic carbon
(POC) produced within the superficial ocean. POC mineralization has
a major impact on oxygen availability and on organic carbon sequestration in sediments, therefore reliable estimates of POC degradation
extent and rate are critical for understanding the carbon cycle. Intrinsic lability of POC constituents and environmental conditions induce
wide variations in POC mineralization rate and extent; both aspects
remain poorly apprehended.
Assessing modifications in the lipid patterns during degradation can
provide valuable insight into the degradation status of the organic
matter. While this approach has been documented at the molecular
level, there is a lack of data on the degradability for a wide range of
lipid classes. In order to address this issue, we studied degradation of
organic carbon and changes in lipid composition at markedly different
time scales: during plankton decay experiments and during early diagenesis in sediments.
Planktonic material was degraded in aerobic conditions representative
of surface and deep-sea conditions, from weeks to months, respectively.
Assuming first order kinetics, degradation rates showed that organic
carbon decay is a two-fold process: an initial rapid decay is followed by
a slower one. Rates of POC mineralization in sediment are 4 to 7 orders
of magnitude smaller than those obtained from plankton decay experiments. Predepositional removal of the most labile compounds results
in a more refractory character of sedimentary organics. Both in experiments and in sediments, lipids were extensively degraded, as shown
by decrease in their concentrations. In addition, lipid degradation did
not lead to enrichment in any specific lipid class: hydrolysed lipid
forms associated with bacterial activity were not showed to accumulate.
However, during plankton decay in deep waters, an enrichment in bacterial biomarkers could be observed within phospholipid-ester linked
fatty acids, analysed by GC and GC/MS after separation by preparative
adsorption chromatography. This evolution trend was not observed in
sediments, beyond the superficial layer. Results underline that changes
in lipid composition at the molecular level appear more sensitive than
at the lipid class level to perceive biodegradation.
27
Tracking marine lipid degradation trends
by latroscan analyses and by molecular
composition of fatty acids
L. Méjanelle, L. Pinturier-Geiss, J. Laureillard, A. Saliot
Université de Paris 6, laboratoire de physique et chimie marines, case 134, 4 place Jussieu,
75252 Paris Cedex 05, France - mejanel@ccr.jussieu.fr
Bacteria play a key role in the recycling of particulate organic carbon
(POC) produced within the superficial ocean. POC mineralization has
a major impact on oxygen availability and on organic carbon sequestration in sediments, therefore reliable estimates of POC degradation
extent and rate are critical for understanding the carbon cycle. Intrinsic lability of POC constituents and environmental conditions induce
wide variations in POC mineralization rate and extent; both aspects
remain poorly apprehended.
Assessing modifications in the lipid patterns during degradation can
provide valuable insight into the degradation status of the organic
matter. While this approach has been documented at the molecular
level, there is a lack of data on the degradability for a wide range of
lipid classes. In order to address this issue, we studied degradation of
organic carbon and changes in lipid composition at markedly different
time scales: during plankton decay experiments and during early diagenesis in sediments.
Planktonic material was degraded in aerobic conditions representative
of surface and deep-sea conditions, from weeks to months, respectively.
Assuming first order kinetics, degradation rates showed that organic
carbon decay is a two-fold process: an initial rapid decay is followed by
a slower one. Rates of POC mineralization in sediment are 4 to 7 orders
of magnitude smaller than those obtained from plankton decay experiments. Predepositional removal of the most labile compounds results
in a more refractory character of sedimentary organics. Both in experiments and in sediments, lipids were extensively degraded, as shown
by decrease in their concentrations. In addition, lipid degradation did
not lead to enrichment in any specific lipid class: hydrolysed lipid
forms associated with bacterial activity were not showed to accumulate.
However, during plankton decay in deep waters, an enrichment in bacterial biomarkers could be observed within phospholipid-ester linked
fatty acids, analysed by GC and GC/MS after separation by preparative
adsorption chromatography. This evolution trend was not observed in
sediments, beyond the superficial layer. Results underline that changes
in lipid composition at the molecular level appear more sensitive than
at the lipid class level to perceive biodegradation.
27