25th International Meeting on Organic Geochemistry IMOG 2011

P-429
Microbial diversity and organic matter cycling of methanerelated
seabed seepage structures in Irish waters
Shane O' Reilly 1 , Michal Szpak 1 , Xavier Monteys 2 , Christopher Allen 3 , Brian Kelleher 1
1 Dublin City University, Dublin, Ireland, 2 Geological Survey of Ireland, Dublin, Ireland, 3 Queen's University
Belfast, Belfast, United Kingdom (corresponding author:brian.kelleher@dcu.ie)
Introduction: Seabed seepage structures –
pockmarks and methane-derived authigenic
carbonate (MDAC) mounds in Irish waters have been
investigated using � 13 C monitoring of lipid biomarkers,
denaturing gradient-gel electrophoresis (DGGE) and
phylogenetic analysis of bacterial and archaeal 16S
rRNA genes. In Irish waters, pockmarks have been
documented in the Malin Sea (Monteys et al, 2008),
the Porcupine Bank (Games, 2001) and in the W.
Irish Sea. In the Irish Sea at the Codling Fault Zone
(CFZ) gas seepage, and anaerobic oxidation of
methane) has facilitated the formation of c. 30 MDAC
mounds (Croker et al. 2005). Selected data from
pockmarks in the Malin Sea and Dunmanus Bay, and
MDACs in the Irish Sea are presented here.
Methods: SEM was performed using a Hitachi
S3400-N. Lipids were extracted by modified
Bligh/Dyer or ultrasonic-assisted extraction and nonextractable
lipids were obtained from base-/acid-
hydrolysis of residues. Desulphurized extracts were
fractionated, derivitized and analysed on an Agilent
6890N/5975C GC-MS coupled to an Isoprime 100
irMS. DNA was extracted and purified according to
Zhou et al (1996). 16S bacterial and archaeal rRNA
genes were PCR-amplified using universal primers
(63f/1387r and Arch-25f/Arch-907r). DGGE was
performed on nested GC-clamp PCR products (CBS
Scientific DGGE 2401). 16S rDNA clone libraries
were created using CloneJET PCR cloning kit
(Fermentas), clustering by restriction analysis, and
representative clones were sequenced, and analysed
using NCBI BLAST, ClustalW and MEGA4 software.
Results
Figure 1: MDAC SEM Images A. Quartz cemented by aragonite &
dolomite crystals. B. Aragonite crystals & framboidal pyrite.
Total
Br- Br-
PLFA SATFA MUFA PUFA SATFA UFA δC 13
MDAC 1.83 0.49 0.43 n.d. 0.67 n.d -27.6
Pockmark 13.84 3.44 2.35 0.74 6.07 0.17 -27.7
Table 1: MDAC and Dunmanus PLFA abundances (�g g -1 ) and
average � 13 C values. (SATFA- saturated FA, MUFA- monounsaturated FA, PUFApolyunsaturated
FA, Br-SATFA- branched saturated FA, Br-UFA- branched unsaturated FA)
Figure 2: Dendrogram comparing DGGE profiles in Dunmanus Bay
pockmark field (GC04, GC09, GC10) and control (GC14)
2mbsf 6mbsf
Species
Clones
%
Total
Clones
%
Total
Psychrobacter sp. 35 54 22 44
Sulfitobacter sp. 9 14 13 26
Alcanovirax borkumensis SK2 4 6 - -
Acinetobacter baumannii 3 5 - -
Geobacillus sp. 3 5 - -
Stenotrophomonas maltophilia 2 3 - -
Aromatoleum aromaticum 1 2 - -
Marinomonas sp. 1 2 - -
Pseudoalteromonas halo. 1 2 2 4
Thiobacillus thioparus - - 2 4
Variovorax paradoxus - - 1 2
Colwellia sp. - - 1 2
Uncultured α-proteobacterium - - 2 4
Table 2: Bacterial species vertical distribution in Malin pockmark
Discussion: PLFA and DGGE profiles indicate a
more diverse bacterial population in the Dunmanus
pockmarks, compared to the MDAC site and a lower
bacterial abundance in the MDAC (Table 1.). DGGE
profiles show a statistically heterogenous bacterial,
but homogenous archaeal community in the
Dunmanus pockmarks compared to the surrounding
environment and interestingly, the opposite within the
MDAC (Figure 2.). DGGE band sequencing indicate
dominant bacteria within the Dunmanus pockmark
field are Achromobacter and Stenotrophomonas sp.
16S rRNA bacterial phylogenetic analysis in the Malin
pockmark show dominant species belong to
Psychrobacter and Sulfitobacter sp., which decrease
and increase in abundance with depth, respectively.
Notably, minor species composition is also markedly
different (Table 2.).
References
1. Croker, P.F. et al. (2005) SEA6 Report 2. Games,
K.P. (2001) Geol. Soc. Of London 3. Monteys , X. et
al. (2008) OSP-01, 33rd Inter. Geol. Congr., Oslo 4.
Zhou, J. et al. (1996) Appl. Environ. Microbiol. 62:316-
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