Paleopleurocapsa Wopfnerii gen. et sp. nov.: A Late Precambrian Alga and Its Modern Counterpart

Silicified dolomite of the approximately one billion year old Skillogalee Dolomite of the Adelaide Geosyncline, South Australia, contains organically preserved microfossils of a structurally complex, crustose pleurocapsalean cyanophyte, herein described as Paleopleurocapsa wopfnerii. Although actual cell contents have been degraded, lamellar sheath material faithfully preserves the morphology of the alga. Comparison with specimens of the modern genus Pleurocapsa Thuret demonstrates affinities at the family level and quite possibly even generic identity.Organismic and Evolutionary Biolog

Le phycologiste Pierre Compère: sa contribution aux études des cyanobactéries

At the occasion of the 80th birthday of Pierre Compère, his rich career as a phycologist and cyanobacteriologist is placed in the context of the advances of the scientific theories, the evolution of the cyanobacterial taxonomy and the nomenclatural discussions linked to the utilization of two different Codes of nomenclature.Taxonomie des cyanobactérie

Dinitrogen-Fixing Cyanobacteria in Microbial Mats of Two Shallow Coral Reef Ecosystems

Dinitrogen-fixing organisms in cyanobacterial mats were studied in two shallow coral reef ecosystems: La Reunion Island, southwestern Indian Ocean, Sesoko (Okinawa) Island, and northwestern Pacific Ocean. Rapidly expanding benthic miniblooms, frequently dominated by a single cyanobacterial taxon, were identified by microscopy and molecular tools. In addition, nitrogenase activity by these blooms was measured in situ. Dinitrogen fixation and its contribution to mat primary production were calculated using 15N2 and 13C methods. Dinitrogen-fixing cyanobacteria from mats in La Reunion and Sesoko showed few differences in taxonomic composition. Anabaena sp. among heterocystous and Hydrocoleum majus and Symploca hydnoides among nonheterocystous cyanobacteria occurred in microbial mats of both sites. Oscillatoria bonnemaisonii and Leptolyngbya spp. occurred only in La Reunion, whereas Hydrocoleum coccineum dominated in Sesoko. Other mats dominated by Hydrocoleum lyngbyaceum, Phormidium laysanense, and Trichocoleus tenerrimus occurred at lower frequencies. The 24-h nitrogenase activity, as measured by acetylene reduction, varied between 11 and 324 nmoles C2H2 reduced µg−1 Chl a. The highest values were achieved by heterocystous Anabaena sp. performed mostly during the day. Highest values for nonheterocystous cyanobacteria were achieved by H. coccineum mostly during the night. Daily nitrogen fixation varied from nine (Leptolyngbya) to 238 nmoles N2µg−1 Chl day−1 (H. coccineum). Primary production rates ranged from 1,321 (S. hydnoides) to 9,933 nmoles C µg−1 Chl day−1 (H. coccineum). Dinitrogen fixation satisfied between 5% and 21% of the nitrogen required for primary production.Ocean Development Sub-Committee of France–Japan S&T Cooperation; Mitsubishi cooperation; The Ministry of Education, Science, Sport, and Culture of Japan; Hanse Wissenschaftskolleg; Delmenhorst and Alexander-von-Humboldt Foundation; Bad Godesberg; Germany supported collaborative research on cyanobacterial diversit

Decastronema kotori n. gen., n. comb., une cyanobactérie des tapis algaires des plates-formes carbonatées crétacées, et ses analogues modernes

Ce fossile fut décrit pour la première fois en 1959 sous le nom d'Aeolisaccus kotori RADOIČIĆ, une nouvelle espèce rapportée à un vers fossile énigmatique, Aeolisaccus ELLIOTT. En 1975, DE CASTRO reconnaissait la nature microbienne de ce fossile, une cyanobactérie très proche du genre actuel Scytonema. Cet organisme est fréquemment observé dans les séries carbonatées des plates-formes mésozoïques d'Europe méridionale. Le présent travail confirme l'interprétation de DE CASTRO. L'examen au MEB montre la remarquabe préservation de l'architecture originelle de ces fossiles et permet d'établir des rapprochements significatifs avec les nombreuses espèces modernes de Scytonema participant à l'élaboration des tapis algaires dans les zones d'estran de l'île d'Andros sur la plate-forme carbonatée des Bahamas. L'établissement des affinités taxinomiques des fossiles et la reconstitution des environnements qu'ils occupaient ont été effectués en comparant les morphologies des fossiles et de leurs analogues actuels, et en prenant également en considération leurs contextes sédimentaires respectifs. En s'appuyant sur ces comparaisons, nous concluons que ces organismes vivaient dans un milieu péritidal et qu'ils ont été enfouis, puis fossilisés en eaux peu profondes sur une plate-forme carbonatée ancienne. Nous proposons le transfert formel de ce fossile dans un nouveau genre de cyanobactéries fossiles créé pour cette occasion et nommé Decastronema n. gen. en l'honneur du Professeur Piero DE CASTRO pour sa contribution à la paléontologie.The fossil renamed here was first described in 1959 as Aeolisaccus kotori RADOIČIĆ, a new species of a problematic fossil worm, Aeolisaccus ELLIOTT. In 1975 DE CASTRO recognized the true relationships of this microbial fossil: a cyanobacterium related closely to the modern genus Scytonema. The fossil is common in the sediments of the Mesozoic carbonate platforms of southern Europe. This contribution confirmed DE CASTRO's interpretation, determined, using the high resolution of the SEM, the extent to which these fossils have preserved their original architecture, and investigated their presumed modern counterparts among the abundant mat-forming species of Scytonema on the intertidal flats of Andros Island, a part of the Bahama carbonate platform. The systematic affinities of the fossil and the environments it inhabited were reconstructed by comparing the morphology of the fossils to that of their modern counterparts, along with their respective sedimentary contexts. Based on these comparisons, we conclude that the organism lived in a peritidal environment and was buried and fossilized in the shallow waters of an ancient carbonate platform. A formal transfer of the fossil to a new genus of fossil cyanobacteria thereby designated as Decastronema gen. nov. is proposed, honoring the contribution of Prof. Piero DE CASTRO to paleontology

Contribution of cyanobacteria to the building of travertines in a calcareous stream

The ambient temperature travertine deposits of the calcareous Hoyoux River (Modave, Belgium) and several tributaries are organized and promoted by the filamentous cyanobacterium identified by its morphotype and ecological properties as Phormidium cf. incrustatum. A combination of techniques was used to study this biotope: physico-chemical parameters and CO2 measurements, Scanning and Transmission Electron Microscopy, RAMAN microspectroscopy. A molecular diversity study with pyrosequencing of the cyanobacterial 16S rRNA is in progress. A potential candidate was isolated in culture.Caractérisation des processus de fossilisation dans les roches calcaires et évolution des cyanobactéries impliquées dans la biominéralisatio

First Evidence of Palytoxin and 42-Hydroxy-palytoxin in the Marine Cyanobacterium Trichodesmium

Marine pelagic diazotrophic cyanobacteria of the genus Trichodesmium (Oscillatoriales) are widespread throughout the tropics and subtropics, and are particularly common in the waters of New Caledonia. Blooms of Trichodesmium are suspected to be a potential source of toxins in the ciguatera food chain and were previously reported to contain several types of paralyzing toxins. The toxicity of water-soluble extracts of Trichodesmium spp. were analyzed by mouse bioassay and Neuroblastoma assay and their toxic compounds characterized using liquid chromatography coupled with tandem mass spectrometry techniques. Here, we report the first identification of palytoxin and one of its derivatives, 42-hydroxy-palytoxin, in field samples of Trichodesmium collected in the New Caledonian lagoon. The possible role played by Trichodesmium blooms in the development of clupeotoxism, this human intoxication following the ingestion of plankton-eating fish and classically associated with Ostreopsis blooms, is also discussed

Critères génétiques et morphologiques dans la taxonomie des Cyanophytes/Cyanobactéries

Molecular techniques have introduced new approaches to the phylogeny and taxonomy of Cyanophyta/Cyanobacteria. One method, the sequencing of the 16S ribosomal RNA, has been applied to 29 cyanophyte strains and produced interesting results (TOMIOKA & SUGIURA 1983, GIOVANNONI et al. 1988). Integration of this new, taxonomically useful information with the results of the classical morphological analyses traditionally used in the taxonomy of cyanophytes is the subject of this paper. Advantages and limitations of different approaches are discussed, and conflicts as well as consensus between morphological properties of the strains under study, and their position in the phylogenetic tree of GIOVANNONI et al. (1988) are reviewed

Biochemical control of calcium carbonate precipitation in modern lagoonal microbialites, Tikehau atoll, French Polynesia

Hemispheroidal domes (microbialites) produced by natural populations of filamentous cyanobacteria belonging to four distinct Phormidium species, and one probable new species of Schizothrix were collected alive from 0-25 m depth habitates in the lagoon of Tikehau atoll (Tuamotu, French Polynesia). This study aims to establish the biochemical control on in-situ carbonate precipitation processes ("organomineralization" processes) occuring merely in the alveolate network of non-coalescent microfibrils that characterizes the degraded parts of the microbialite domes. The comparison between amino acid and monosaccharide composition of purified cyanobacterially produced organic matter and that of intramineral (soluble and insoluble) organic matrices associated with carbonate precipitates emphasizes the importance of dicarboxylic (aspartic and glutamic) acids, released by the decay of cyanobacterial sheaths, in CaCO3 formation and demonstrates that the in situ precipitation of ultra-fine micrites is a highly selective process regarding the available external organic matter. This diagenetic process is thought to result from incipient hydrolysis of cyanobacterial S-layer proteins attached to extracellular polysaccharide fibrils composing the sheath. Taxonomic affinity of cyanobacterial populations responsible for microbialite construction is one of the major factors allowing biochemical discrimination of in-situ precipitated carbonates, indicating that specific mucilages or their degradational products are guiding forces for the calcification processes. Another possible source for the formation of carbonate-associated organic matrices is derived from metabolites (e.g. mucus) released in water by lagoonal dwelling benthic organisms