25th International Meeting on Organic Geochemistry IMOG 2011

P-445
The influence of geological and geochemical processes on
microbial biogeography at hydrothermal vents on the Mid-
Atlantic Ridge: evidence from the distribution of intact polar
lipids
Robert Gibson 1 , Marcel van der Meer 1 , Ellen Hopmans 1 , Anna-Louise Reysenbach 2 ,
Stefan Schouten 1 , Jaap Sinninghe Damsté 1
1 NIOZ Royal Netherlands Institute for Sea Research, 't Horntje, Netherlands, 2 Department of Biology,
Portland State University, Portland, United States of America (corresponding author:Robert.gibson@nioz.nl)
Hyperthermophilic microbes are known to
occupy the deepest branches of the 16s rRNA gene
based universal tree of life. Thus, microbial
communities associated with modern deep-sea
hydrothermal vents likely closely resemble the life
which occupied the early Earth. However, the factors
that affect the distribution and diversity of microbial
communities in modern hydrothermal settings are not
well constrained. Important questions such as what
effect does fluid chemistry have on microbial
populations and who are the key players in each
particular setting have yet to be addressed. In an
attempt to answer some of these questions, we have
investigated the intact polar lipid (IPL) composition of
twelve vent deposits from two distinct hydrothermal
vent fields located on the Mid-Atlantic Ridge (MAR).
The two locations investigated are the ‗Rainbow‘
hydrothermal vent field (RHF), an ultra-mafic system
characterised by high-temperature vent fluids (up to
365 0 C), which contain large amounts of hydrogen,
methane and other reduced carbon compounds. The
second location is the ‗Lucky Strike‘ hydrothermal
vent field (LSHF), a basalt-hosted system where vent
fluids reach up to 300 0 C and contain relatively high
amounts of H2S but lower methane and much lower
hydrogen than RHF.
Analysis of vent material from both RHF and
LSHF showed large difference in the abundance of
lipids produced by Archaea and Bacteria (Figure 1). In
the RHF samples approximately 50% of the IPLs are
from Archaeal origin, while in LSHF this is usually less
than 10%. One other clear difference between the two
vent fields is that vent deposits from RHF contain a
predominance of IPLs with archaeol and macrocyclic
archaeol core lipids, which are absent in vent material
from the LSHF.
The results of the IPL analysis are in good
agreement with those of molecular analysis of the
same samples by 454 pyrosequencing of the
hypervariable V4 region of Archaeal rRNA genes.
Members of the Methanocaldococcaceae and
Methanococcaceae were identified as important
community members in RHF, but were absent in
LSHF (Flores et al., unpublished data). The presence
of Methanocaldococcaceae, Methanococcaceae and
macrocyclic archaeol IPLs in RHF and absence in
LSHF seems to be directly linked to the hydrogen
availability at both vent fields.
Bacterial IPLs containing PE, PG and PC
headgroups were also identified and likely derive from
members of the epsilonproteobacteria, which are
known to be prevalent in hydrothermal settings.
The general matching of IPL composition
with those of community diversity studies of RHF and
LSHF (Flores et al., unpublished data) suggest IPLs
are applicable as live markers in these environmental
settings and provide complimentary information to
studies of microbial communities.
RHF
LSHF
1
3
5
6
7
8
9
11
12
0 20 40
% composition
60 80 100
Archaeal IPLs Bacterial IPLs IPLs of unknown origin
Figure 1. IPL composition, based on total peak
response area, of MAR vent deposits as percentage
of total identifiable IPLs. Three samples (2, 4 and 10)
did not contain any identifiable IPLs.
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