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See detailPhototrophic green algae in Mid-Proterozoic oceans
Sforna, Marie-Catherine ULiege; Loron, Corentin ULiege; Demoulin, Catherine ULiege et al

Poster (2020, January)

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See detailAntarctic cyanobacteria sources of biosignatures
Lara, Yannick ULiege; Demoulin, Catherine ULiege; Lambion, Alexandre ULiege et al

Conference (2019, September 05)

The high UV intensities and extreme seasonality make some of Antarctic habitats interesting to the study life adaptive strategies in extreme conditions, and the biosignatures that can be preserved. In ... [more ▼]

The high UV intensities and extreme seasonality make some of Antarctic habitats interesting to the study life adaptive strategies in extreme conditions, and the biosignatures that can be preserved. In Antarctica, most of the surface, lacustrine and endolithic photosynthetic niches are occupied by cyanobacteria, which are well equipped to survive cold, desiccation or UV exposure. To provide a better understanding of the cyanobacteria survival strategies to extreme conditions, we used transmitted light and TEM microscopy as well as high-throughput sequencing technologies on the Antarctic lineage Phormidesmis priestleyi. We observed and characterized the production of a gloeocapsin-like UV-screening pigment and compared it to the pigment produced by Gloeocapsa alpina. Cyanobacteria are considered to be the inventors of oxygenic photosynthesis and therefore played a pivotal role in early Life and Earth evolution during the Precambrian. However, to perform photosynthesis in the UV exposure of the Early Earth unprotected by an ozone layer, their ancestors must have developed multiple molecular strategies. The presence of a gloeocapsin-like pigment in different cyanobacterial lineages may suggest its early production by their common ancestor, potentially present before the oxidation of the atmosphere. In Polar regions, low temperatures lead to the success of particular organisms featuring adaptations to molecular and cellular disturbances such as rigidity of membranes, reduction of enzyme-catalyzed reactions, and solute transport. Our results underline the importance of functional categories of genes involved in the production of key molecules for the survival of polar P. priestleyi (e.g. exopolysaccharides, chaperone proteins, fatty acids and phospholipids). The study of Antarctic cyanobacteria is promising to find new analog biosignatures for Life in rocky habitable planets. This project is supported by the mini-ARC PUMA (ULiège, Belgium). [less ▲]

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See detailCyanobacteria evolution: Insight from the fossil record
Demoulin, Catherine ULiege; Lara, Yannick ULiege; Cornet, Luc ULiege et al

in Free Radical Biology and Medicine (2019), 140

Cyanobacteria played an important role in the evolution of Early Earth and the biosphere. They are responsible for the oxygenation of the atmosphere and oceans since the Great Oxidation Event around 2.4 ... [more ▼]

Cyanobacteria played an important role in the evolution of Early Earth and the biosphere. They are responsible for the oxygenation of the atmosphere and oceans since the Great Oxidation Event around 2.4 Ga, debatably earlier. They are also major primary producers in past and present oceans, and the ancestors of the chloroplast. Nevertheless, the identification of cyanobacteria in the early fossil record remains ambiguous because the morphological criteria commonly used are not always reliable for microfossil interpretation. Recently, new biosignatures specific to cyanobacteria were proposed. Here, we review the classic and new cyanobacterial biosignatures. We also assess the reliability of the previously described cyanobacteria fossil record and the challenges of molecular approaches on modern cyanobacteria. Finally, we suggest possible new calibration points for molecular clocks, and strategies to improve our understanding of the timing and pattern of the evolution of cyanobacteria and oxygenic photosynthesis. © 2019 The Authors [less ▲]

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See detailBiosignatures of modern and fossil cyanobacteria
Demoulin, Catherine ULiege; Lara, Yannick ULiege; François, Camille ULiege et al

Poster (2018, March 21)

The Proterozoic is an important eon for the evolution of early life on Earth, and especially for the diversification of cyanobacteria, a major group of photosynthetic microorganisms. In paleontology, much ... [more ▼]

The Proterozoic is an important eon for the evolution of early life on Earth, and especially for the diversification of cyanobacteria, a major group of photosynthetic microorganisms. In paleontology, much effort and work are devoted to the study of cyanobacteria, due to their key-role in the oxygenation of the atmosphere and oceans during the GOE (Great Oxidation Event, around 2.4 Ga). Moreover, the development of oxygenated ecological niches is one of the factors linked to the diversification of eukaryotes. However, identifying extremely old microfossil structures as cyanobacteria remains often disputed. The oldest fossil cyanobacterium (~ 1.9 Ga) determined so far with certainty is Eoentophysalis belcherensis Hofmann, a microorganism forming mats and colonies in silicified stromatolites from the Belcher Islands, Hudson Bay, Canada [1]. Its identification as a cyanobacterium relies mainly on morphological comparison to a modern cyanobacterium, Entophysalis Ercegović [2]. In this context, our research project, financed by the ERC StG ELiTE, mainly aims at characterizing the biosignatures of Proterozoic cyanobacteria in order to get new insights into the origin and early evolution of cyanobacteria and oxygenic phtosynthesis. Methodologically, we are using optical microscopy, electron microscopy (SEM and TEM) and Raman and FTIR microspectroscopy techniques, applied on modern specimens and microfossils. This approach is expected to test the biological nature of Paleoproterozoic and younger microstructures, to resolve the affinities of possible prokaryotic microfossils and, thus, to assess their taxonomic placement among cyanobacteria. [less ▲]

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See detailBiosignatures of modern and fossil cyanobacteria
Demoulin, Catherine ULiege; Lara, Yannick ULiege; François, Camille ULiege et al

Conference (2018)

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See detailFeeding and ecological diversity of Tournaisian holocephalans: insights from dental microwear
Demoulin, Catherine ULiege; Derycke, Claire; Michel, Christian ULiege et al

Conference (2017)

At the end of the Devonian, several profound extinctions affected a large number of marine groups. However, some of them, such as holocephalan chondrichtyans, showed a great diversification during the ... [more ▼]

At the end of the Devonian, several profound extinctions affected a large number of marine groups. However, some of them, such as holocephalan chondrichtyans, showed a great diversification during the recovery of the ecosystems, during the Tournaisian. Despite the fact that a large taxic diversity has been documented for these holocephalans; their ecological diversity is however poorly known, because the shape of isolated teeth can be a poor predictor of the ecology of these animals. Microwear analysis has the potential to reveal distinct diets and actual use of teeth in these extinct animals during the Tournaisian. We analysed the microwear of Tournaisian holocephalans from the Tournai and Ourthe formations of Belgium. Dental microwears were observed qualitatively on 20 teeth with a scanning electron microscope and mapped and analysed in detail for 7 of them with ArcMap software. While pits are almost totally absent in our sample, our microwear dataset revealed two populations of scratches with distinct length distributions. We suggest that these populations were produced by two different mechanisms. The first population contains mainly long scratches (>0.2 mm, up to 2.0 mm) that are often oriented 40° to 70° compared to the anteroposterior axis of the tooth. We propose that these scratches would have been produced by trituration. The second population comprises almost exclusively of short scratches (<0.2 mm) especially abundant on the mesial face of the teeth and preferentially oriented subparallel to the anteroposterior axis. They would have been produced when the holocephalans dug into sea bottom sediments while searching for food. To identify materials that might have caused the observed microwear, we compared the hardness of the holocephalan orthodentine, making the bulk of the crown of holocephalan teeth, and materials present in their environment. The skeleton of a wide series of marine organisms (crinoids, brachiopods, molluscs) is composed of calcite or aragonite, which appears to be slightly harder than holocephalan orthodentine. These materials may thus scratch holocephalan teeth but are hardly able to produce pits because of the small difference in hardness. Tournaisian holocephalans were thus probably feeding on benthic faunae and they likely dug in the sediment at the search of food. If correct, this might rule out prey items located clearly above the sea floor, such as ammonioids or high-stalked crinoids. However, most of our specimens showed similar microwear features, which prevents us to highlight ecological differences between the taxa we sampled. [less ▲]

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See detailFeeding and ecological diversity of Tournaisian holocephalans: approach through the study of dental microwear
Demoulin, Catherine ULiege; Derycke, Claire; Michel, Christian ULiege et al

Scientific conference (2017)

At the end of the Devonian, several profound extinctions affected a large number of marine groups. However, some of them, such as holocephalan chondrichtyans, showed a great diversification during the ... [more ▼]

At the end of the Devonian, several profound extinctions affected a large number of marine groups. However, some of them, such as holocephalan chondrichtyans, showed a great diversification during the recovery of the ecosystems, during the Tournaisian. Despite the fact that a large taxic diversity has been documented for these holocephalans; their ecological diversity is however poorly known, because the shape of isolated teeth can be a poor predictor of the ecology of these animals. Microwear analysis has the potential to reveal distinct diets and actual use of teeth in these extinct animals during the Tournaisian. We analysed the microwear of Tournaisian holocephalans from the Tournai and Ourthe formations of Belgium. Dental microwears were observed qualitatively on 20 teeth with a scanning electron microscope and mapped and analysed in detail for 7 of them with ArcMap software. While pits are almost totally absent in our sample, our microwear dataset revealed two populations of scratches with distinct length distributions. We suggest that these populations were produced by two different mechanisms. The first population contains mainly long scratches (>0.2 mm, up to 2.0 mm) that are often oriented 40° to 70° compared to the anteroposterior axis of the tooth. We propose that these scratches would have been produced by trituration. The second population comprises almost exclusively of short scratches (<0.2 mm) especially abundant on the mesial face of the teeth and preferentially oriented subparallel to the anteroposterior axis. They would have been produced when the holocephalans dug into sea bottom sediments while searching for food. To identify materials that might have caused the observed microwear, we compared the hardness of the holocephalan orthodentine, making the bulk of the crown of holocephalan teeth, and materials present in their environment. The skeleton of a wide series of marine organisms (crinoids, brachiopods, molluscs) is composed of calcite or aragonite, which appears to be slightly harder than holocephalan orthodentine. These materials may thus scratch holocephalan teeth but are hardly able to produce pits because of the small difference in hardness. Tournaisian holocephalans were thus probably feeding on benthic faunae and they likely dug in the sediment at the search of food. If correct, this might rule out prey items located clearly above the sea floor, such as ammonioids or high-stalked crinoids. However, most of our specimens showed similar microwear features, which prevents us to highlight ecological differences between the taxa we sampled. [less ▲]

Detailed reference viewed: 89 (24 ULiège)