Browsing by Author "Ertefai, T"

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    Lipid abundance and stable isotopic composition of photosynthetic microbial mats in hypersaline embayments at Shark Bay, Western Australia
    (Australasian Environmental Isotope Conference, 2009-12-03) Ertefai, T; Jahnert, R; Grice, K; Dodson, JR; Collins, L
    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.