Change in light quality due to a blue-green pigment, marennine, released in oyster-ponds: effect on growth and photosynthesis in two diatoms, Haslea ostrearia and Skeletonema costatum

Two prominent diatoms encountered in oyster-ponds,Haslea ostrearia and Skeletonema costatum,were grown in batch and in a semi-continuous modeunder light of different spectral quality, white, blueor blue-green. The last corresponded to white lightmodified by a water-soluble pigment, marennine,produced by H. ostrearia. After acclimation tothe different light treatments, the growth rates ofboth species showed little variation with respect tolight quality. The parameters for photosynthesisvs irradiance curves were very similar in H. ostrearia grown under the three light conditions,whereas S. costatum the maximum photosyntheticcapacity (on a chlorophyll a basis) wassignificantly reduced under blue-green light. Fluorescence analyses confirmed the data forphotosynthesis, with the operational fluorescenceyield decreasing faster with increasing irradiance inS. costatum grown under blue-green light. InH. ostrearia, fluorescence yields undersaturating irradiance were closely similar in thethree light conditions. The results are discussed inrelation with the prominent development of H.ostrearia that can outcompete other diatoms inoyster-ponds.     

Campylobacter jejuni: Specific oligonucleotides and DNA probes for use in polymerase chain reaction-based diagnosis

Abstract A 1189 base-pair long DNA fragment, VS1, was isolated from a Campylobacter jejuni CIP 70.2 cosmid library and was found to contain regions specific for this bacterial species. For detection and identification of C. jejuni , two oligonucleotides derived from the VS1 sequence were used as primers in polymerase chain reaction test on genomic DNAs from 38 Campylobacter and from 10 non- Campylobacter strains. A specific, 358 base-pair long DNA fragment was amplified only when C. jejuni DNA was used as a target. The detection limit of the amplification reaction was as low as 1.86 fg DNA, which is the equivalent of one C. jejuni genome.     

The Nutritional Geometry of Resource Scarcity: Effects of Lean Seasons and Habitat Disturbance on Nutrient Intakes and Balancing in Wild Sifakas

Animals experience spatial and temporal variation in food and nutrient supply, which may cause deviations from optimal nutrient intakes in both absolute amounts (meeting nutrient requirements) and proportions (nutrient balancing). Recent research has used the geometric framework for nutrition to obtain an improved understanding of how animals respond to these nutritional constraints, among them free-ranging primates including spider monkeys and gorillas. We used this framework to examine macronutrient intakes and nutrient balancing in sifakas (Propithecus diadema) at Tsinjoarivo, Madagascar, in order to quantify how these vary across seasons and across habitats with varying degrees of anthropogenic disturbance. Groups in intact habitat experience lean season decreases in frugivory, amounts of food ingested, and nutrient intakes, yet preserve remarkably constant proportions of dietary macronutrients, with the proportional contribution of protein to the diet being highly consistent. Sifakas in disturbed habitat resemble intact forest groups in the relative contribution of dietary macronutrients, but experience less seasonality: all groups’ diets converge in the lean season, but disturbed forest groups largely fail to experience abundant season improvements in food intake or nutritional outcomes. These results suggest that: (1) lemurs experience seasonality by maintaining nutrient balance at the expense of calories ingested, which contrasts with earlier studies of spider monkeys and gorillas, (2) abundant season foods should be the target of habitat management, even though mortality might be concentrated in the lean season, and (3) primates’ within-group competitive landscapes, which contribute to variation in social organization, may vary in complex ways across habitats and seasons.     

Global Stability of Reversible Enzymatic Metabolic Chains

We consider metabolic networks with reversible enzymatic reactions. The model is written as a system of ordinary differential equations, possibly with inputs and outputs. We prove the global stability of the equilibrium (if it exists), using techniques of monotone systems and compartmental matrices. We show that the equilibrium does not always exist. Finally, we consider a metabolic system coupled with a genetic network, and we study the dependence of the metabolic equilibrium (if it exists) with respect to concentrations of enzymes. We give some conclusions concerning the dynamical behavior of coupled genetic/metabolic systems.     

When a knockout is an Achilles’ heel: Resistance to one potyvirus species triggers hypersusceptibility to another one in Arabidopsis thaliana

The translation initiation factors 4E are a small family of major susceptibility factors to potyviruses. It has been suggested that knocking out these genes could provide genetic resistance in crops when natural resistance alleles, which encode functional eIF4E proteins, are not available. Here, using the well-characterized Arabidopsis thaliana–potyvirus pathosystem, we evaluate the resistance spectrum of plants knocked out for eIF4E1, the susceptibility factor to clover yellow vein virus (ClYVV). We show that besides resistance to ClYVV, the eIF4E1 loss of function is associated with hypersusceptibility to turnip mosaic virus (TuMV), a potyvirus known to rely on the paralog host factor eIFiso4E. On TuMV infection, plants knocked out for eIF4E1 display striking developmental defects such as early senescence and primordia development stoppage. This phenotype is coupled with a strong TuMV overaccumulation throughout the plant, while remarkably the levels of the viral target eIFiso4E remain uninfluenced. Our data suggest that this hypersusceptibility cannot be explained by virus evolution leading to a gain of TuMV aggressiveness. Furthermore, we report that a functional eIF4E1 resistance allele engineered by CRISPR/Cas9 base-editing technology successfully circumvents the increase of TuMV susceptibility conditioned by eIF4E1 disruption. These findings in Arabidopsis add to several previous findings in crops suggesting that resistance based on knocking out eIF4E factors should be avoided in plant breeding, as it could also expose the plant to the severe threat of potyviruses able to recruit alternative eIF4E copies. At the same time, it provides a simple model that can help understanding of the homeostasis among eIF4E proteins in the plant cell and what makes them available to potyviruses.     

Microperoxidase 8 catalysed nitrogen oxides formation from oxidation of N-hydroxyguanidines by hydrogen peroxide.

Nitric oxide (NO) is a potent intra- and intercellular messenger involved in the control of vascular tone, neuronal signalling and host response to infection. In mammals, NO is synthesized by oxidation of l-arginine catalysed by hemeproteins called NO-synthases with intermediate formation of Nomega-hydroxy-l-arginine (NOHA). NOHA and some hydroxyguanidines have been shown to be able to deliver nitrogen oxides including NO in the presence of various oxidative systems. In this study, NOHA and a model compound, N-(4-chlorophenyl)-N'-hydroxyguanidine, were tested for their ability to generate NO in the presence of a haemprotein model, microperoxidase 8 (MP8), and hydrogen peroxide. Nitrite and nitrate production along with selective formation of 4-chlorophenylcyanamide was observed from incubations of N-(4-chlorophenyl)-N'-hydroxyguanidine in the presence of MP8 and hydrogen peroxide. In the case of NOHA, the corresponding cyanamide, Ndelta-cyano-L-ornithine, was too unstable under the conditions used and l-citrulline was the only product identified. A NO-specific conversion of 2-(4-carboxyphenyl)-4,4,5,5-tetramethylimidazoline-1-oxyl 3-oxide to 2-(4-carboxyphenyl)-4,4,5,5-tetramethylimidazoline-1-oxyl and formation of MP8-Fe-NO complexes were observed by EPR spectroscopy and low-temperature UV/visible spectroscopy, respectively. These results clearly demonstrate the formation of nitrogen oxides including NO from the oxidation of exogenous hydroxyguanidines by hydrogen peroxide in the presence of a minienzyme such as MP8. The importance of the bioactivation of endogenous (NOHA) or exogenous N-hydroxyguanidines by peroxidases of physiological interest remains to be established in vivo.     

Folding and stability of outer membrane protein A (OmpA) from Escherichia coli in an amphipathic polymer, amphipol A8-35

Amphipols are a class of amphipathic polymers designed to maintain membrane proteins in aqueous solutions in the absence of detergents. Denatured β-barrel membrane proteins, like outer membrane proteins OmpA from Escherichia coli and FomA from Fusobacterium nucleatum, can be folded by dilution of the denaturant urea in the presence of amphipol A8-35. Here, the folding kinetics and stability of OmpA in A8-35 have been investigated. Folding is well described by two parallel first-order processes, whose half-times, ~5 and ~70 min, respectively, are independent of A8-35 concentration. The faster process contributed ~55–64 % to OmpA folding. Folding into A8-35 was faster than into dioleoylphosphatidylcholine bilayers and complete at ratios as low as ~0.17 g/g A8-35/OmpA, corresponding to ~1–2 A8-35 molecules per OmpA. Activation energies were determined from the temperature dependence of folding kinetics, monitored both by electrophoresis, which reports on the formation of stable OmpA tertiary structure, and by fluorescence spectroscopy, which reflects changes in the environment of tryptophan side chains. The two methods yielded consistent estimates, namely ~5–9 kJ/mol for the fast process and ~29–37 kJ/mol for the slow one, which is lower than is observed for OmpA folding into dioleoylphosphatidylcholine bilayers. Folding and unfolding titrations with urea demonstrated that OmpA folding into A8-35 is reversible and that amphipol-refolded OmpA is thermodynamically stable at room temperature. Comparison of activation energies for folding and unfolding in A8-35 versus detergent indicates that stabilization of A8-35-trapped OmpA against denaturation by urea is a kinetic, not a thermodynamic phenomenon.