25th International Meeting on Organic Geochemistry IMOG 2011

P-442
Deep-sea benthic archaea recycle relic membrane lipids: insight
from ―in situ 13C-incubation experiment‖ and its lipidomics
Yoshinori Takano 1 , Yoshito Chikaraishi 1 , Nana O. Ogawa 1 , Hidetaka Nomaki 1 , Yuki
Morono 2 , Fumio Inagaki 2 , Kai-Uwe Hinrichs 3 , Nao Ohkouchi 1
1 Japan Agency for Marine-Earth Science & Technology (JAMSTEC), Yokosuka, Japan, 2 Kochi Inst. Core
Research, JAMSTEC, Kochi, Japan, 3 MARUM & Dept. Geosciences, University of Bremen, Bremen,
Germany (corresponding author:takano@jamstec.go.jp)
Introduction
Deep-sea sediments harbour a vast and unusual
biosphere with as yet undetermined importance in the
global carbon cycle. Carbon isotopic signatures of
archaeal intact polar lipids from sediments dominated
by benthic archaeal communities indicate utilization of
sedimentary organic carbon [1]. Since most benthic
archaea are viable but non-culturable microbes and
difficult to study in the laboratory [2], we conducted in
situ 13 C-tracer experiments to determine the metabolic
activity, especially for deep-sea benthic archaea
focused on the biogeochemical processes of specific
membrane lipids.
Experimental
In situ 13 C-tracer experiments during 0-405 days were
performed with the incubation chamber [3] operated
by ROV Hyper-Dolphin and its mother research
vessel Natsushima at Sagami Bay, Japan (35˚00.7‘N,
139˚22.5‘E, depth 1,453 m). 13 C-labeled glucose
(99%, 13 C6H12O6: hereafter, G-n) or 13 C-Chlorella
(99%: ibid, C-n) were injected by the 5mL syringe
attached on the top. The incubation cores and a
reference core were recovered after 9 and 405 days
deployment. After in situ tracer experiments, archaeal
GDGTs (glycerol dialkyl glycerol tetraethers) were
extracted from the core samples and purified by
HPLC/APCI-MS combined with a fraction collector
(Agilent 1100) for compound-specific carbon isotopic
analyses of GDGTs. After ether-bond cleavage
treatment, the intramolecular carbon isotopic
compositions of each isoprenoid (biphytanes; BP[0],
BP[2], BP[3]) and their 2,3-sn-glycerols were also
directly measured by online GC/C/IRMS [4].
Results and Discussion
We found that the 13 C was peculiarly enriched into the
2,3-sn-glycerol backbone (< 2200‰ in G-405; <
3020‰ in C-9) of archaeal membranes during 405
days, while the isoprenoid chain of the membranes
remained unlabelled (i.e., natural abundance). 16S
rRNA and quantitative PCR (qPCR) analysis indicated
a community shift in the composition of the benthic
archaeal community and its abundance (10 5 -10 7
copies g-sed -1 ) during the course of the experiment,
whereas the relative abundances (%) of archaeal
GDGT compositions were almost constant during 405
days. On the basis of the differential uptake of 13 Ctracer,
we suggest that only the glycerol unit is
synthesized de novo, whereas the isoprenoid unit is
recycled from relic archaeal membranes and detritus,
because of the prevalence of these compounds in
marine sediments. We therefore suggest that benthic
archaea build their membranes by recycling
sedimentary relic membrane lipids in order to
minimize the energy expenditure for de novo lipid
synthesis.
References
[1] Biddle, J.F. et al. (2006) PNAS, 103, 3846-3851.
[2] Teske, A. & Sorensen, K.B. (2008) ISME Journal,
2, 3-18. [3] Nomaki, H. et al. (2006) Mar. Ecol. Prog
Ser., 310, 95-108. [4] Takano et al. (2010) Nature
Geosci., 3, 858-861.
Figure 1 Carbon isotopic compositions of
caldarchaeol, crenarchaeol and its intramolecular
moieties (2,3-sn-glycerol and biphytanes: ‰ PDB
scale) at core top section (0-1cm) by in situ 13 Cglucose
experiments during 405 days.
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