Isolation and characterization of nonheterocystous tropical cyanobacteria growing on nitrogen-free medium

Summary Fourteen non-heterocystous cyanobacteria were selected from a continuous waterlogged biotope on a mineral medium free of combined nitrogen. Following morphological characterization, four, nine and one of the strains respectively, were assigned to sections I, II and III of a new cyanobacterial classification. Their phenotypic properties, including growth rates, photoheterotrophy, phycobiliprotein content, antibiotic resistance and toxin production were determined. Three strains were found to harbour one to three plasmids of low molecular weight.

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Resumen Mediante un medio mineral sin nitrogéno combinado se seleccionaron catorce cepas de cianobacterias no heterocísticas a partir de un biotopo permanentemente inundado. Apartir de sus carácterísticas morfológicas cuatro, nueve y una de las cepas fueron asignadas respectivamente a las secciones I, II y III de un nuevo sistema para la clasificación de cianobacterias. Se determinaron sus principales características fenotípicas, incluyendo tasas de crecimiento, fotoheterotrofia, contenido en ficobiliproteína, resistencia a antibióticos y producción de toxinas. Tres de las cepas contenían de uno a tres plásmidos de bajo peso molecular.

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Résumé Quatorze souches de cyanobactéries non-hétérocystées ont été isolées d'un biotope inondé sur un milieu minéral dépourvu d'azote combiné. Après détermination de leurs caractères morphologiques, respectivement quatre, neuf et une des souches ont été assignées aux sections I, II et III de la classification des cyanobactéries. Leurs propriétés phénotypiques telles que taux de croissance, photohétérotrophie, contenu en phycobiliprotéines, résistance aux antibiotiques et la production de toxine ont été déterminées. Trois des souches contiennent de un à trois plasmides de faible masse moléculaire.

     

Characterization of stable conformational variants of erythrocyte carbonic anhydrases.

Limiting viscosity numbers of bovine and ovine erythrocytes carbonic anhydrase variants were calculated by the objective method of comparing viscosimetric data obtained from low-activity-human erythrocyte carbonic anhydrase and its natural variant. Shifts of mobilities and isoelectric points are shown for all species variants, but variations of limiting viscosity numbers were only detected for human and bovine variants. Results of the study are consistent with the observation that variants arise by deamidation of erythrocyte carbonic anhydrases, and that deamidation is responsible for changes in structure and hydration (i. e. "conformational" modifications). Thus, all the variants so far investigated are stable conformational variants or erythrocyte carbonic anhydrases.     

Capacités reproductrices et descendance de poulets ayant subi un transfert de cellules germinales primordiales durant la vie embryonnaire

Résumé Des cellules germinales primordiales de Dindon, transférées par injection intravasculaire à des embryons de Poulet préalablement stérilisés, peuvent subir une maturation complète dans les gonades de l'hôte et fournir des gamètes plus ou moins aptes à la fécondation.Les spermatozoïdes résultants ont fécondé des oeufs de poule avec une fréquence plus grande que les spermatozoïdes normaux de Dindon, mais sans permettre un développement embryonnaire plus important ou plus normal. Cependant, on n'est pas parvenu à leur faire féconder des oeufs de dinde.Les ufs résultants ont montré parfois un vitellus anormal et n'ont été pondus que durant 7 mois. Mis en présence de spermatozoïdes de coq, ils ont été quelquefois fécondés (ou peutêtre simplement activés), mais ils n'ont jamais fourni d'embryons. Fécondés par des spermatozoïdes de Dindon, ils ont fourni des embryons, parfois anormaux, qui ont atteint dans le meilleur cas le 15è jour d'incubation (stade 38 HH). Certainespraepennae de l'embryon qui a atteint ce stade montraient une pigmentation rouge brun qui ne peut pas être déterminée par le génotype du zygote (celui d'un Dindon de race blanche) et qui rappelle le phénotype de la mère nourricière (une poule rouge brun).A la suite de transferts intraspécifiques de cellules germinales primordiales, on a pu obtenir la maturation d'ovocytes de Rhode Island Red à l'intérieur d'un ovaire de Wyandotte Blanche (chez deux poules) et vice versa (chez une poule). La ponte a également été possible, mais à une fréquence souvent inférieure à la normale.Lorsqu'une poule Wyandotte Blanche, portant des ovocytes de Rhode Island Red a été accouplée à un coq Rhode Island Red normal, le duvet de leurs descendants s'est montré plus clair que celui des poussins Rhode Island Red dans un cas, mais il a été remplacé ensuite par un plumage rouge brun conforme au génotype.Lorsqu'une poule Rhode Island Red, portant des ovocytes de Wyandotte Blanche a été accouplée à un coq Wyandotte Blanche normal, le duvet de leurs descendants n'a jamais été conforme au génotype. Il présentait toujours du pigment noir plus ou moins étendu et, dans un cas, du pigment rouge brun, qui sont tous deux présents chez la mère nourricière. On ne connaît ni l'origine ni le mécanisme d'un tel transfert de pigments, qui ne représente peut-être qu'un effet transitoire affectant le duvet de la première génération. La crête, quant à elle, s'est toujours montrée conforme au génotype d'origine.

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Reproductive capacity and offspring of chickens submitted to a transfer of primordial germ cells during embryonic life

Summary Turkey primordial germ cells transfered by intravascular injection to previously sterilized chick embryos can undergo complete maturation inside the host's gonads and can give rise to gametes which are more or less suitable for fertilization.The resulting spermatozoa fertilized hen eggs at a higher frequency than normal turkey spermatozoa, but without allowing a longer or a more normal development. However, it was impossible to fertilize turkey eggs with them.The resulting eggs sometimes had an abnormal-looking yolk and were laid during the first 7 months only. Brought in contact with chicken spermatozoa, they were fertilized (or perhaps merely activated), but they never gave rise to embryos. Fertilized by turkey spermatozoa, they developed into embryos, sometimes abnormal, which in the best case reached the 15th day of incubation (stage 38 HH). Somepraepennae of the latter embryo showed a red-brown pigment which cannot be determined by the genotype of the zygote (a white turkey's) and which resembled the phenotype of the foster mother (a red-brown hen).After intraspecific transfer of primordial germ cells, maturation of Rhode Island Red oöcytes inside a Wyandotte White ovary (in two hens) and vice versa (in one hen) was achieved. Laying was also possible but often at a lower frequency than normal.When a Wyandotte White hen bearing Rhode Island Red oöcytes was mated with a normal Rhode Island cock, the down of their offspring looked brighter than Rhode Island Red chicken's in one case, but it was subsequently replaced by red-brown feathers according to the genotype.When a Rhode Island Red hen bearing Wyandotte White oöcytes was mated with a normal Wyandotte White cock, the down of their offspring was never in agreement with the genotype. It always showed a black pigment over more or less large areas and, in one case, a red-brown pigment, both of which were present in the foster mother. The origin and the mechanism of such a transfer of pigments are not understood. It might represent merely a temporary effect acting upon the down of the first generation. As far as the comb is concerned, it was always in agreement with the original genotype.

     

In Situ Fe and S isotope analyses in pyrite from the 3.2 Ga Mendon Formation (Barberton Greenstone Belt,South Africa): Evidence for early microbial iron reduction

On the basis of phylogenetic studies and laboratory cultures, it has been proposed that the ability of microbes to metabolize iron has emerged prior to the Archaea/Bacteria split. However, no unambiguous geochemical data supporting this claim have been put forward in rocks older than 2.7–2.5 giga years (Gyr). In the present work, we report in situ Fe and S isotope composition of pyrite from 3.28‐ to 3.26‐Gyr‐old cherts from the upper Mendon Formation, South Africa. We identified three populations of microscopic pyrites showing a wide range of Fe isotope compositions, which cluster around two δ⁵⁶Fe values of ?1.8‰ and +1‰. These three pyrite groups can also be distinguished based on the pyrite crystallinity and the S isotope mass‐independent signatures. One pyrite group displays poorly crystallized pyrite minerals with positive Δ³³S values > +3‰, while the other groups display more variable and closer to 0‰ Δ³³S values with recrystallized pyrite rims. It is worth to note that all the pyrite groups display positive Δ³³S values in the pyrite core and similar trace element compositions. We therefore suggest that two of the pyrite groups have experienced late fluid circulations that have led to partial recrystallization and dilution of S isotope mass‐independent signature but not modification of the Fe isotope record. Considering the mineralogy and geochemistry of the pyrites and associated organic material, we conclude that this iron isotope systematic derives from microbial respiration of iron oxides during early diagenesis. Our data extend the geological record of dissimilatory iron reduction (DIR) back more than 560 million years (Myr) and confirm that micro‐organisms closely related to the last common ancestor had the ability to reduce Fe(III).     

Does Optic Nerve Head Surface Topography Change Prior to Loss of Retinal Nerve Fiber Layer Thickness: A Test of the Site of Injury Hypothesis in Experimental Glaucoma

Purpose

To test the hypothesis that optic nerve head (ONH) deformation manifesting as changes in its mean surface height precedes thinning of the peripapillary retinal nerve fiber layer (RNFL) in experimental glaucoma (EG).

Methods

68 rhesus macaque monkeys each had three or more baseline imaging sessions under manometric intraocular pressure (IOP) control to obtain average RNFL thickness (RNFLT) and the ONH surface topography parameter mean position of the disc (MPD). Laser photocoagulation was then applied to the trabecular meshwork of one eye to induce chronic, mild-to-moderate IOP elevation and bi-weekly imaging continued. Event analysis was applied to determine for each parameter when an ‘endpoint’ occurred (signficant change from baseline) for eight different endpoint criteria. Specificity was assessed in the group of 68 fellow control eyes. Classical signal detection theory and survival analysis were used to compare MPD with RNFLT.

Results

Regardless of the endpoint criterion, endpoints were always more frequent for MPD than for RNFLT. The discriminability index (d’) was 2.7 ± 0.2 for MPD and 1.9 ± 0.2 for RNFLT (p<0.0001). Endpoints were reached by MPD an average of 1-2 months earlier than by RNFLT (p<0.01). At the onset of the first specific, detectable MPD change in EG eyes, there was still no significant change in RNFLT on average (p=0.29) and only 25% of individual eyes exhibited signficant reduction. In contrast, at onset of signficant RNFLT change, MPD had already changed an average of 101 µm from baseline (p<0.0001) and 71% of the individual eyes had exhibited significant change. The magnitude of MPD change was more than could be explained on the basis of axon loss alone.

Conclusions

This study demonstrates that the average surface height of the ONH changes prior to any detectable loss of average peripapillary RNFL thickness in non-human primate eyes with experimental glaucoma.     

A comprehensive examination of the network position hypothesis across multiple river metacommunities

The hierarchical branching nature of river networks can have a strong influence on the assembly of freshwater communities. This unique structure has spurred the development of the network position hypothesis (NPH), which states that the strength of different assembly processes depends on the community position in the river network. Specifically, it predicts that 1) headwater communities should be exclusively controlled by the local environment given that they are more isolated and environmentally heterogeneous relative to downstream reaches. In contrast, 2) downstream communities should be regulated by both environmental and dispersal processes due to increased connectivity given their central position in the riverscape. Although intuitive, the NPH has only been evaluated on a few catchments and it is not yet clear whether its predictions are generalizable. To fill this gap, we tested the NPH on river dwelling fishes using an extensive dataset from 28 French catchments. Stream and climatic variables were assembled to characterize environmental conditions and graph theory was applied on river networks to create spatial variables. We tested both predictions using variation partitioning analyses separately for headwater and downstream sites in each catchment. Only 10 catchments supported both predictions, 11 failed to support at least one of them, while in 7 the NPH was partially supported given that spatial variables were also significant for headwater communities. We then assembled a dataset at the catchment scale (e.g. topography, environmental heterogeneity, network connectivity) and applied a classification tree analysis (CTA) to determine which regional property could explain these results. The CTA showed that the NPH was not supported in catchments with high heterogeneity in connectivity among sites. In more homogeneously connected catchments, the NPH was only supported when headwaters were more environmentally heterogeneous than downstream sites. We conclude that the NPH is context dependent even for taxa dispersing exclusively within streams.