25th International Meeting on Organic Geochemistry IMOG 2011

P-446
Distribution of ammonia-oxidizing archaea and anammox
bacteria in the Arabian Sea OMZ using a combined approach
based on intact polar lipids and abundance/expression of
specific genes
Laura Villanueva, Angela Pitcher, Ellen Hopmans, Stefan Schouten, Jaap Sinninghe
Damsté
Royal Netherlands Institute for Sea Research, Den Burg, Texel, Netherlands (corresponding
author:laura.villanueva@nioz.nl)
Oxygen Minimum zones (OMZs) play a critical role in
the marine microbial community structuring and global
biochemical cycles [1]. Two microbial groups
inhabiting OMZs are receiving special attention
because of their role in the marine carbon and
nitrogen cycles: Anammox Bacteria and ammoniaoxidizing
Archaea (AOA, Thaumarchaeota). AOA
oxidize ammonia aerobically to nitrite by the ammonia
monooxygenase enzyme (amoA) and they play a
major role in oceanic nitrification due to their high
affinity for ammonia [2]. Anammox Bacteria display an
chemoautotrophic metabolism combining ammonia
and nitrite to form N2 (N-loss to the atmosphere) [3].
Both groups of microbes also produce specific
biomarker lipids, i.e. AOA produce crenarchaeol while
anammox Bacteria produce ladderane lipids. Previous
studies have suggested that AOA and nitrifiers can
provide nitrite for anammox Bacteria. However, little is
known about their distribution and interaction.
In this study, we investigated the distribution,
abundance and activity of AOA and anammox
Bacteria in the OMZ of the Arabian Sea. We applied a
combined approach based on quantification of both
intact polar lipids (IPLs) and DNA/RNA (functional)
genes. IPLs consist of the core membrane lipids still
covalently linked to polar head groups which are
relatively labile, and thus represent lipids synthesized
by living, or recently living cells. We used a newly
developed HPLC/MS 2 method to target AOA-specific
crenarchaeol IPLs as well as a previously published
method targeting C20-[3]-monoether ladderane lipid
with a phosphatidylcholine headgroup (PC-monoether
ladderane) specific for anammox Bacteria. Targeting
genes at the level of DNA (16S rDNA gene and
metabolic genes such as AOA amoA gene and
hydrazine oxidoreductase (hzo) anammox) provided
information on the abundance and metabolic activity
of these microbial groups. The results showed that
hexose-phosphohexose (HPH)-crenarchaeol showed
a substantial increase from the surface waters with a
maximum relative abundance at 170 m depth, which
was coincident with copy numbers and expression
(RNA) of thaumarchaeotal 16S rDNA and amoA
genes. On the contrary, lowest values of AOA genes
and IPLs were detected in the core of the OMZ (600–
750 m) where oxygen concentrations are minimal.
Anammox bacterial markers (PC-monoether
ladderane, 16S rRNA anammox and hzo gene) covaried
well throughout the water column and, in
contrast to AOA, maximum abundances were
observed in the core of the OMZ.
Our results thus show that specific phospholipids can
be excellent tracers of active anammox bacteria and
AOA. The occurrence of HPH-crenarchaeol in all AOA
samples screened to date, the labile nature of the
phosphate-ester bond, and the correlation with
nucleic acid-based profiles, render HPH-crenarchaeol
as the most fitting biomarker to track living AOA in
comparison with hexose-based IPLs. Furthermore,
our findings indicate that the distribution and activity
of anammox Bacteria is concentrated at the core of
the OMZ, which can be an indication of their
importance in removing nitrogen in anoxic waters.
Although AOA could theoretically provide substrates
for anammox and thus occupy similar niches, our
results indicate that this is not the case evidenced by
the large vertical segregation (>400 m) of their niches.
Ref: [1] Diaz & Rosenberg (2008) Science 321:926.
[2] Arrigo (2005) Nature 437:349. [3] Kuypers et al
(2003) Nature 422:608. [4] This work published :
Pitcher et al. (2011) ISME Journal
572