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See detailPaleobiology of an Ediacaran acanthomorphic acritarch
Domino, Samuel ULiege; Loron, Corentin ULiege; Sforna, Marie-Catherine ULiege et al

Poster (2021, July)

The Ediacaran is a crucial time of changes in climatic and redox conditions, nutrient availability, and diversification of eukaryotes, including planktonic algae and the first unambiguous metazoans ... [more ▼]

The Ediacaran is a crucial time of changes in climatic and redox conditions, nutrient availability, and diversification of eukaryotes, including planktonic algae and the first unambiguous metazoans. During this period, new and highly diverse organic-walled eukaryotic microfossils appear worldwide, but their identity remains enigmatic. They are called the “Doushantuo-Pertatataka type Acanthomorphic acritarchs” (DPA). Their morphological complexity (diverse types of processes expanding from the vesicle wall) evidences their eukaryoticity. Several hypotheses for their affinity have been proposed, tentatively interpreting a few of these microfossils as eggs of metazoans [1,2] or cysts of chloroplastid green algae [2-5], but they remain ambiguous. To test these hypotheses, we present a morphological, ultrastructural and spectroscopic characterisation of one of the most emblematic DPA acritarchs, Gyalosphaeridium pulchrum. Such analytical combination has never been performed all together on a DPA taxon. The fossils come from the Munta-1 drillcore from the Tanana formation in the eastern Officer basin in Australia. Quantitative analyses [6] of microfossils through the drillcore revealed assemblages dominated by simple smooth-walled sphaeromorphs, and less abundant but very diverse and exquisitely preserved acanthomorphs, previously reported [7]. Drawing on our analyses and previous work, we discuss the possible diagnostic combinations of characters to pinpoint the clade to which the microfossils may belong. This approach, extended to more DPA taxa, will permit to constrain the appearance of eukaryotic clades in the Ediacaran and their role in the complexification of late Precambrian ecosystems. It will also provide guidelines for future identification of similarly enigmatic microfossils, frequent in Precambrian and Paleozoic strata. [1] Cohen, Knoll & Kodner (2009), Proceedings of the National Academy of Sciences 106, 6519–6524. [2] Willman (2009), Geobiology 7, 8–20. [3] Marshall, Javaux, Knoll & Walter (2005), Precambrian Research 138, 208–224. [4] Moczydłowska & Liu (2021), Geological Magazine, doi:10.1017/S0016756820001405. [5] Willman & Moczydłowska (2007), Lethaia 40, 111–123. [6] Calers (2020), Diversification de la biosphère après un impact de météorite (Acraman, Australie) au Néoprotérozoïque, M. Sc. thesis, Université de Liège. [7] Grey (2005), Memoirs of the Association of Australasian Palaeontologists 31, 439 pp. [less ▲]

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See detailTesting the cellular nature of large (>10µm) spheroids in the ~3.4 Ga Strelley Pool Formation
Coutant, Maxime ULiege; Lepot, Kevin; Fadel, Alexandre et al

Conference (2021, July)

The oldest traces of life on Earth are still highly debated and both biotic and abiotic arguments are proposed for isotopic, mineral and morphological biosignatures1,2. The ca. 3.4 Strelley Pool Formation ... [more ▼]

The oldest traces of life on Earth are still highly debated and both biotic and abiotic arguments are proposed for isotopic, mineral and morphological biosignatures1,2. The ca. 3.4 Strelley Pool Formation (SPF), in Western Australia, is well-known for its stromatolites and for its diverse assemblages of carbonaceous microstructures. Some of these microstructures have been claimed as the oldest microfossils2,3,. The SPF lies in greenstone belts of the Pilbara craton, and comprises (volcano)clastic material, silicified sediments, dolomite (including stromatolites) and precipitated cherts (including stromatolites). Metamorphism grades from to greenschist to amphibolite facies and it is cut across by siliceous and siliceous-carbonaceous veins4. Such veins may have transported carbonaceous matter into hydrothermally-influenced sediments2,3. For example, microstructures in silicified volcanic clasts of the SPF exhibit morphologies resembling mineral textures associated with organic matter5, such as simple spheres or lenses. Here we rigorously describe unusual spherical microstructures which differ from the abundant, smaller (≤10 µm) spheres previously reported in cherts of the SPF3. These microstructures are imaged and analyzed through a combination of in situ techniques, including optical microscopy and confocal laser scanning microscopy (CLSM), electron backscattered diffraction (EBSD), and transmitted electron microscopy (TEM) on ultrathin (focused ion beam) sections (FIB). This approach yields an effective visualization of carbonaceous microstructures and their relationships with quartz crystal grains down to the nanoscale. It revealed a wealth of textural features that allow us to classify the spheroids into three new types (+sub-types) and to discuss possible cellular origin versus mineral morphogenesis in presence of organic compounds. [less ▲]

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See detailEarly traces of the three domains of life : evidence and challenges
Javaux, Emmanuelle ULiege

Scientific conference (2021, April 20)

Deciphering the early record and evolution of life is crucial to characterize plausible and reliable biosignatures of microbial life and understand the evolution of the Earth biosphere. We can then ... [more ▼]

Deciphering the early record and evolution of life is crucial to characterize plausible and reliable biosignatures of microbial life and understand the evolution of the Earth biosphere. We can then address questions regarding the conditions for life to appear and develop on a planetary body (habitability), or the probability for an extraterrestrial biosphere to develop complex metabolism or complex life. This research is also critical to develop life detection strategies, instruments and missions applicable to other planets of the solar system such as the ongoing and future Martian missions, and to atmospheres of rocky exoplanets, and to samples returned to Earth, as space agencies have recently come to appreciate. Considerable debates still exist regarding the age and origins of the three domains of life (Archaea, Bacteria, Eucarya), as well as the evolution of cellular life before LUCA. Possible isotopic, biosedimentary, molecular and morphological traces of life suggest the presence of microbial communities in diverse environments. However, these traces may in some cases also be produced by abiotic processes or later contamination, leaving a controversy surrounding the earliest record of life on Earth. Before a microstructure can be accepted as a microfossil, a series of approaches need to be employed to prove its endogenicity, syngenicity, and biological origin, as well as to falsify an abiotic explanation for the observed morphologies or chemistries. These micro- to nano-scale analyses complement the macro-scale characterisation of the geological context, as the environmental conditions will determine the plausibility of ancient habitats and the conditions of fossilisation. Experimental taphonomy also helps understanding the processes of decay and preservation of biosignatures during fossilization. Interpreting the identity and paleobiology of unambiguous traces may also be challenging. However, regardless of taxonomy, the paleobiological record can provide direct evidence for extinct clades and/or for the minimum age of evolution of biological innovations. Reassessing the evidence of early life is challenging but essential and timely for the quest of life’s first traces and evolution, both on Earth and beyond. [less ▲]

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See detailThe earliest traces of the three domains of life: evidence and challenges
Javaux, Emmanuelle ULiege

Conference (2021, January 27)

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See detailUV-screening pigment enabling ancient photosynthesis
Lara, Yannick ULiege; Mc Cann, Andréa ULiege; Malherbe, Cédric ULiege et al

Conference (2021)

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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 detailThe Proterozoic Arctic Canada as a case study for the evolution and diversity of early Eukaryotes.
Loron, Corentin ULiege; Halverson, Galen; Rainbird, Rob et al

Poster (2020)

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See detailDiversification of complex life on the early Earth: the Proterozoic of Artic Canada as a case study
Loron, Corentin ULiege; Halverson, Galen; Rainbird, Rob et al

Poster (2020)

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See detailInterpreting the biological affinities of early Eukaryotes
Loron, Corentin ULiege; François, Camille; Rainbird, Rob et al

Conference (2020)

Detailed reference viewed: 49 (9 ULiège)
See detailPaleobiology and Evolution of early eukaryotes
Javaux, Emmanuelle ULiege

Scientific conference (2019, November 22)

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See detailOrigin and evolution of early eukaryotes: insight from the fossil record.
Javaux, Emmanuelle ULiege

Scientific conference (2019, October 25)

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See detailBiodiversity of Cyanobacteria and associated microbiome in the BCCM/ULC Culture Collection
Ahn, Anne-Catherine ULiege; Cornet, Luc ULiege; Beets, Kim ULiege et al

Poster (2019, October 18)

Cyanobacteria are a phylum of photosynthetic bacteria that played an important role in the evolution of the planet by oxygenating its early atmosphere and provoking the Great Oxydation Event around 2.3 ... [more ▼]

Cyanobacteria are a phylum of photosynthetic bacteria that played an important role in the evolution of the planet by oxygenating its early atmosphere and provoking the Great Oxydation Event around 2.3 billion years ago. Early cyanobacteria were the ancestors of plastids and thus, at the origin of the highly successful algae and plants. Nowadays, they still are the basis of the food chain in many biotopes, as long as there is liquid water, light, air and some minerals. Some cyanobacterial taxa are very resistant to harsh environmental conditions, and thus, grow in polar, hypersaline, alkaline and/or arid biotopes, but also in spatial conditions. Furthermore, they are also a prolific source of secondary compounds with bioactivies. The BCCM/ULC public collection funded by the Belgian Science Policy Office since 2011 presently includes 224 cyanobacterial strains, with 140 being of Antarctic origin (catalogue: http://bccm.belspo.be/catalogues/ulc-catalogue-search). The strains are unicyanobacterial but not axenic, due to the well known difficulties of purifying them. Morphological identification showed that the strains belong to the orders of Synechococcales, Oscillatoriales, Pleurocapsales, Chroococcidiopsidales and Nostocales. Furthermore, 16S rRNA and ITS sequences of the strains are being characterized. Recent sequencing efforts increased the amount of available 16S rRNA sequences of BCCM/ULC strains to 190. Those sequences belong to 75 OTUs (groups of sequences with > 99 % 16S rRNA similarity), which represents a quite large diversity. To better characterize the microbiome of the cultures, a metagenomic analysis was performed for 12 polar or subpolar strains and three temperate ones, including three early-branching organisms that will be useful for phylogenomics. The design of a specific metagenomic pipeline enabled the easy recovery of the cyanobacterial genomes from the non-axenic cultures. In parallel, 31 genomes of co-cultivated bacteria (12 nearly complete) from the same cultures were determined. They mostly belonged to Bacteroidetes and Proteobacteria, some of them being very closely related, in spite of sometimes geographically distant sampling sites (Cornet et al. 2018). In summary, the BCCM/ULC public collection serves as a Biological Resource Centre to conserve ex situ and document the biodiversity of cyanobacteria and their microbiomes, as well as a repository for discovery of novel bioactive compounds. Cornet, L., Bertrand, A., Hanikenne, M., Javaux, E., Wilmotte, A., & Baurain, D. (2018). Metagenomic assembly of new (sub)polar Cyanobacteria and their associated microbiome from non-axenic cultures. Microbial Genomics.4. DOI 10.1099/mgen.0.000212. [less ▲]

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