Lipid abundance and stable isotopic composition of photosynthetic microbial mats in hypersaline embayments at Shark Bay, Western Australia
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Date
2009-12-03
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Australasian Environmental Isotope Conference
Abstract
Photosynthetic microbial mats and living
stromatolites/microbialites in hypersaline embayments
at Shark Bay, Western Australia are significant
microbial niches. Cyanobacteria together with a
consortium of microbes form microbialites/stromatolites.
These organisms are important as it is believed they
evolved some 3.5 billion years ago. In this study,
modern analogues of the fossilised counterparts
(Pilbara, WA) are being investigated to provide clues to
the origin of life on early Earth.
The distribution and growth of different microbial
mats across the hypersaline coastal plain of Shark Bay
is thought to be attributed to a complex network of
physicochemical factors [1]. The relationship of internal
mat structures (lithification), geochemical conditions
and microbial community structure, are not well
understood. A complex interplay of different metabolic
pathways, microbial physiologies (including of
cyanobacteria, sulphur cycling organisms and Archaea)
may play a role in the differentiation of the lithifying vs.
non-lithifying mats [2].
In this study, we have applied a variety of different
analytical techniques to address the biological,
geochemical and geological makeup of microbial mats
from four embayments differing in salinity levels. We
wish to link the different morphotypes of microbial mats
with their biology and chemistry to understand the
regional occurrence and enhance our geological
interpretation.
Biomarker abundances determined by both, liquid
chromatography (LC), gas chromatography (GC) and
mass spectrometry (MS) provide clues to the microbial
community structure. Here we report for first time the
presence of intact polar lipids (IPLs) and
bacteriohopanepolyols (BHPs) by LC-MS specific to
cyanobacteria and other microbes. Compound-specific
isotope analysis (CSIA) of carbon and hydrogen reflects
the metabolic pathways and the hydrologic conditions
(including salinity). Hydro Pyrolysis (HyPy) experiments
of the non-extractable organics reveal biomarkers
similar to those reported in the rock record.
The IPLs of microbial mats collected at the internal
pond of Garden Point (salinity ~40-80‰, depending on
season and tide) shows a complex distribution of
different glyco- and phospholipids (Fig. 1). These IPLs
can be attributed to different groups of microorganisms.
Phospholipids, and specifically PG, are present in all
phototrophic bacteria [3]. The presence of ornithine
lipids and the sulpholipid SQ-DAG has been described
in oxygenic and anoxygenic phototrophs, such as
cyanobacteria and purple (non-) sulphur bacteria [3, 4].
Latter group uses sulphur, sulphide or hydrogen as an
electron donor which do not evolve oxygen as a byproduct,
and causes mat colouration.
With the analysis of carbon and hydrogen stable
isotopes of the hydrolysed biolipids, we can gain further
insights into the biogeochemical conditions and
biochemical pathways. We especially focus on the
domain Archaea, as their role in the Shark Bay
microbialites are poorly understood [e.g. 2]. The role of
methane cycling Archaea is being investigated via
labelling experiments using 13C-enriched bicarbonate
and methane. Hydrogenotrophic methanogenesis and
methanotrophy will be quantified via solvent extraction
of biolipids and the uptake of labelled substrates into
their specific biolipids by CSIA.
Description
Keywords
Lipids, Stable isotopes, Saline aquifers, Bays, Western Australia, Australia, Cyanobacteria
Citation
Ertefai, T., Jahnert, R., Grice, K., Dodson, J., & Collins, L. (2009). Lipid abundance and stable isotopic composition of photosynthetic microbial mats in hypersaline embayments at Shark Bay, Western Australia. Paper presented to The 10th Australasian Environmental Isotope Conference and 3rd Australasian Hydrogeology Research Conference, Resources and Chemistry Precinct, Curtin University Perth, Western Australia 1st – 3rd December 2009. (pp. 12).