Lipid Biomarker and Isotopic Study of Community Distribution and Biomarker Preservation in a Laminated Microbial Mat from Shark Bay, Western Australia

Modern microbial mats from Shark Bay present some structural similarities with ancient stromatolites; thus, the functionality of microbial communities and processes of diagenetic preservation of modern mats may provide an insight into ancient microbial assemblages and preservation. In this study, the vertical distribution of microbial communities was investigated in a well-laminated smooth mat from Shark Bay. Biolipid and compound-specific isotopic analyses were performed to investigate the distribution of microbial communities in four distinct layers of the mat. Biomarkers indicative of cyanobacteria were more abundant in the uppermost oxic layer. Diatom markers (e.g. C25 HBI alkene, C20:4ω6 and C20:5ω3 polar lipid fatty acids (PLFAs)) were also detected in high abundance in the uppermost layer, but also in the deepest layer under conditions of permanent darkness and anoxia, where they probably used NO3 − for respiration. CycC19:0, an abundant PLFA of purple sulfur bacteria (PSB), was detected in all layers and presented the most 13C-depleted values of all PLFAs, consistent with photoautotrophic PSB. Sulfur-bound aliphatic and aromatic biomarkers were detected in all layers, highlighting the occurrence of early sulfurisation which may be an important mechanism in the sedimentary preservation of functional biolipids in living and, thus, also ancient mats

Organic geochemical studies of modern microbial mats from Shark Bay: Part I: Influence of depth and salinity on lipid biomarkers and their isotopic signatures

The present study investigated the influence of abiotic conditions on microbial mat communities from Shark Bay, a World Heritage area well known for a diverse range of extant mats presenting structural similarities with ancient stromatolites. The distributions and stable carbon isotopic values of lipid biomarkers [aliphatic hydrocarbons and polar lipid fatty acids (PLFAs)] and bulk carbon and nitrogen isotope values of biomass were analysed in four different types of mats along a tidal flat gradient to characterize the microbial communities and systematically investigate the relationship of the above parameters with water depth. Cyanobacteria were dominant in all mats, as demonstrated by the presence of diagnostic hydrocarbons (e.g. n-C17 and n-C17:1). Several subtle but important differences in lipid composition across the littoral gradient were, however, evident. For instance, the shallower mats contained a higher diatom contribution, concordant with previous mat studies from other locations (e.g. Antarctica).Conversely, the organic matter (OM) of the deeper mats showed evidence for a higher seagrass contribution [high C/N, 13C-depleted long-chain n-alkanes]. The morphological structure of the mats may have influenced CO2 diffusion leading to more 13C-enriched lipids in the shallow mats. Alternatively, changes in CO2 fixation pathways, such as increase in the acetyl COA-pathway by sulphate-reducing bacteria, could have also caused the observed shifts in δ13C values of the mats. In addition, three smooth mats from different Shark Bay sites were analysed to investigate potential functional relationship of the microbial communities with differing salinity levels. The C25:1 HBI was identified in the high salinity mat only and a lower abundance of PLFAs associated with diatoms was observed in the less saline mats, suggesting a higher abundance of diatoms at the most saline site. Furthermore, it appeared that the most and least saline mats were dominated by autotrophic biomass using different CO2 fixation pathways

Nano-porous pyrite and organic matter in 3.5-billion-year-old stromatolites record primordial life

Stromatolites of the similar to 3.5 billion-year-old Dresser Formation (Pilbara Craton, Western Australia) are considered to be some of Earth's earliest convincing evidence of life. However, uniquely biogenic interpretations based on surface outcrops are precluded by weathering, which has altered primary mineralogy and inhibited the preservation of microbial remains. Here, we report on exceptionally preserved, strongly sulfidized stromatolites obtained by diamond drilling from below the weathering profile. These stromatolites lie within undeformed hydrothermal-sedimentary strata and show textural features that are indicative of biogenic origins, including upward-broadening and/or upward-branching digitate forms, wavy to wrinkly laminae, and finely laminated columns that show a thickening of laminae over flexure crests. High-resolution textural, mineralogical, and chemical analysis reveals that the stromatolites are dominated by petrographically earliest, nano-porous pyrite that contains thermally mature, N-bearing organic matter (OM). This nano-porous pyrite is consistent with a formation via sulfidization of an originally OM-dominated matrix. Evidence for its relationship with microbial communities are entombed OM strands and filaments, whose microtexture and chemistry are consistent with an origin as mineralized biofilm remains, and carbon isotope data of extracted OM (delta C-13(OM) = -29.6 parts per thousand +/- 0.3 parts per thousand VPDB [Vienna Peedee belemnite]), which lie within the range of biological matter. Collectively, our findings provide exceptional evidence for the biogenicity of some of Earth's oldest stromatolites through preservation of OM, including microbial remains, by sulfidization

The Maia detector and event mode

A decade ago, prototypes of the Maia detector successfully demonstrated a fresh approach to X-ray fluorescence microscopy (XFM) imaging that combined a massively parallel detector architecture with dedicated pulse shaping and capture on each channel, asynchronous acquisition of X-rays as an event stream, and real-time processing of the event data [1, 2]. Today, a number of XFM beamlines that raster scan a sample through a focused X-ray beam to construct images of element concentration and chemical state use a 384-detector array version of Maia for high-throughput, high-definition XFM. The beamlines include those at the Australian Synchrotron (AS) in Melbourne [3], the PETRA III synchrotron at DESY, Hamburg [4], the CHESS synchrotron at Cornell University in Ithaca [5], and the NSLS-II at Brookhaven National Laboratory (BNL) in New York..

Diel fluctuations in solute distributions and biogeochemical cycling in a hypersaline microbial mat from Shark Bay,WA

Studying modern microbial mats can provide insights into how microbial communities interact with biogeochemical cycles. High-resolution, two-dimensional distributions of porewater analytes were determined in the upper three layers of a modern microbial mat from Nilemah, Shark Bay, Western Australia, using colorimetric diffusive equilibration in thin film (DET) and diffusive gradients in thin film (DGT) techniques. The colorimetric DET and DGT techniques were used to investigate the co-distributions of sulfide, iron(II), and phosphate and the alkalinity. Two-dimensional distributions of sulfide, iron(II) and phosphate showed a high degree of spatial heterogeneity under both light and dark conditions. However, average concentration profiles showed a clear shift in overall redox conditions between light and dark conditions. During light deployments, iron(II) and sulfide concentrations were generally low throughout the entire microbial mat. In contrast, during dark deployments, when anoxic conditions prevailed, higher concentrations of iron(II) and sulfide were observed and the sulfide boundary migrated towards the upper layer of the mat. Similar to the iron(II) profile, the phosphate profile showed an increase in concentration at night, suggesting that phosphate was released through the dissolution of iron–phosphate complexes under anoxic conditions.However, two-dimensional distributions revealed that hot spots of phosphate and iron(II) did not coincide, suggesting that porewater phosphate was mainly regulated by diel metabolic changes in the mat. Alkalinity profiles also demonstrated an increase in concentration at night, probably related to high rates of sulfate reduction under dark conditions. Complimentary microelectrode measurements of oxygen and sulfide confirmed that light-limited microbial communities play a significant role in regulating porewater solute concentrations, especially through photosynthetic activity that supports rapid re-oxidation of sulfide during the day. Sulfide was not detected in the upper layers (ca. 4 mm) of the mat by microelectrode measurements, but was found at those depths by the time-integratedDGT measurements. Complimentary silver foil deployments also showed a 2D distribution of sulfate-reducing activity occurring under oxic conditions in the top layers. DGT, O2 and sulfide microelectrode profiles and silver foils confirmed hotspots of sulfide production coinciding with cyanobacterial photosynthesis. Two-dimensional porewater analyte distributions showed significant small-scale heterogeneity, highlighting the complexity of such dynamic ecosystems and the advantage of two-dimensional methods

Biodiversity inventories in high gear: DNA barcoding facilitates a rapid biotic survey of a temperate nature reserve

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