Selection of Culture Conditions and Cell Morphology for Biocompatible Extraction of β-Carotene from Dunaliella salina

Biocompatible extraction emerges recently as a means to reduce costs of biotechnology processing of microalgae. In this frame, this study aimed at determining how specific culture conditions and the associated cell morphology impact the biocompatibility and the extraction yield of β-carotene from the green microalga Dunaliella salina using n-decane. The results highlight the relationship between the cell disruption yield and cell volume, the circularity and the relative abundance of naturally permeabilized cells. The disruption rate increased with both the cell volume and circularity. This was particularly obvious for volume and circularity exceeding 1500 µm³ and 0.7, respectively. The extraction of β-carotene was the most biocompatible with small (600 µm³) and circular cells (0.7) stressed in photobioreactor (30% of carotenoids recovery with 15% cell disruption). The naturally permeabilized cells were disrupted first; the remaining cells seems to follow a gradual permeabilization process: reversibility (up to 20 s) then irreversibility and cell disruption. This opens new carotenoid production schemes based on growing robust β-carotene enriched cells to ensure biocompatible extraction.     

A molecular test to identify resistance alleles at the amplified esterase locus in the mosquito Culex pipiens

A new PCR/RFLP method is presented to identify all described alleles involved in resistance at the Ester locus in the mosquito Culex pipiens. The efficiency of this method as well as its advantages compared with the traditional identification technique (starch gel electrophoresis) have been tested in four natural samples from France, Tunisia and California. This simple and fast molecular test is a very convenient tool for studies in field populations and laboratory strains. © 2000 Society of Chemical Industry     

Release of dissolved organic carbon and nitrogen from forest floors in relation to solid phase properties,respiration and N-mineralization

Dissolved organic carbon (DOC) and nitrogen (DON) are important components of the carbon and nitrogen turnover in soils. Little is known about the controls on the release of DOC and DON from forest floors, especially about the influence of solid phase properties. We investigated the spatial variation of the release of DOC and DON from Oe and Oa forest floor samples at a regional scale. Samples were taken from 12 different Norway spruce sites with varying solid phase properties, including C/N ratio, pH, different fractions of extractable carbon and exchangeable cations. Most of these solid phase properties are available for large forested areas of Europe in high spatial resolution. The samples were incubated at water holding capacity for eight weeks at 15°C and then extracted with an artificial throughfall solution to measure DOC and DON release. The rates of soil respiration and N-mineralization were determined to estimate soil microbial activity. The release of DOC and DON from Oe samples was two- to threefold higher than from Oa samples. The amounts released differed by one order of magnitude among the sites. The DOC/DON ratios in the percolates of the Oa samples were much higher as compared to the solid phase C/N, indicating different release rates of DOC and DON. In contrast, the DOC/DON ratios of the Oe percolates were in the range of the C/N ratios of the solid phase. The release of DOC and DON from Oe samples was not statistically correlated to any of the measured solid phase parameters, but to N-mineralization. The DOC and DON release from the Oa samples was positively related only to pH and soil respiration. Overall it was not possible to explain the large spatial variation of DOC and DON release by the measured solid phase properties with satisfying accuracy.     

Kinetics of Uptake and Metabolism of Atrazine in Model Plant Systems

The present work concerns atrazine absorption and metabolism by corn (Zea mays.) seedlings immersed in an aqueous medium in comparison with Acer pseudoplatanus cell cultures. At the point of equilibrium, the apparent concentration inside the A. pseudoplatanus cells (with a moderate lipid content: 0·17% of dry weight) was about twice that of the medium. This equilibrium was probably due to a simple partition process; part of the atrazine was dissolved in the cell water and reached the same concentration as in the external medium while the rest was concentrated inside the cellular lipids. The theoretical calculation of the lipid/water partition, taking into account the value of log P measured not with the lipids but with octanol (log P=2·5), gave a value of 1·5 for concentration inside the plant material. Such an equilibrium, resulting from a partition process between water and lipids, was also obtained in non-living corn seedlings. In living seedlings, an over-concentration of radioactivity due to [¹⁴C]atrazine derivatives was rapidly obtained inside roots and shoots giving concentrations respectively 7- and 12-fold higher than that of atrazine in the external medium. This was due to very rapid chemical transformation of atrazine into its hydroxy derivatives, especially hydroxyatrazine. This hydrolysis of atrazine in corn was due to the presence of high levels of benzoxazinone derivatives in corn seedling cells. The hydroxylated metabolites were able to concentrate in the cells very rapidly and were unable to diffuse freely into the external medium. As a consequence, this process facilitated the penetration of large quantities of atrazine which became rapidly hydroxylated, allowing therefore the passive penetration of atrazine to be further improved, since the concentration C₁ in the receiver compartment was always close to zero. The passive transfer of atrazine, following Fick's law: dq/dt=-Pa (C₀–C₁), was therefore optimized. © 1997 SCI.     

Degradation of [14C]Terbuthylazine and [14C]Atrazine in Laboratory Soil Microcosms

The degradation and formation of major chlorinated metabolites of terbuthylazine and atrazine in three soils (loamy clay, calcareous clay and high clay) were studied in laboratory experiments using molecules labelled with ¹⁴C on the s-triazine ring. Soil microcosms were treated with the equivalent of 1 kg ha^-1 of herbicide and incubated in the dark for 45 days at 20(±1)°C. The quantity of [¹⁴C]carbon dioxide evolved in the soils treated with atrazine was negligible and could not be attributed to mineralization of the parent molecule. The mineralization of terbuthylazine accounted for 0·9–1·2% of the initial radioactivity. In the soils studied, the extrapolated half-lives varied from 88 to 116 days for terbuthylazine and 66 to 105 days for atrazine, with no significant differences for the three soils and the two molecules. The deethyl metabolites of the two s-triazines and the deisopropyl-atrazine metabolite appeared during the incubation in the three soils. The completely dealkylated metabolite was not detected in any of the soils. After 45 days of incubation, the non-extractable soil residues for the high clay, loamy clay and calcareous clay soils represented for terbuthylazine, 33·5, 38·3 and 43·1% and for atrazine, 19·8, 20·8 and 22·3% of the initial radioactivity. © 1997 SCI.     

The expansion of the Atlantic–Mediterranean ghost crab Ocypode cursor (Linnaeus, 1758): Distribution,environmental niches and future perspectives

The tufted ghost crab Ocypode cursor (Linnaeus, 1758) found in the Mediterranean Sea and the Atlantic Ocean is currently a great example that elucidates concerns within scientific and conservation communities. This species, native to the subtropical Atlantic Ocean and the warmest southeastern Mediterranean Sea (Egypt), has been extending its distribution in both regions since the 1980s, likely due to the warming sea temperatures. These small nocturn crabs are typically found inhabiting sandy beaches and dune environments. This species is an opportunistic predator eating terrestrial and marine prey, especially on sea turtle eggs. Despite its status as a threatened species by two European conventions, there is a lack of knowledge of its ecology and biology. Sometimes considered as an indicator of good ecological status of beaches where it lives, this ghost crab could nevertheless benefit from climate change to extend its distribution range. This review aims to create a baseline on the current knowledge and gaps in the published scientific literature on the ghost crab. Additionally, through an analysis of the existing literature, we also offer insights into the potential risk of beach erosion associated with the expansion of this species.     

Fucoidans of Moroccan Brown Seaweed as Elicitors of Natural Defenses in Date Palm Roots

Fucoidans from Moroccan brown seaweed Bifurcaria bifurcata and Fucus spiralis were tested for their elicitor activity after their purification and complete characterization. The fucoidans of B. bifurcata (BBF) and of F. spiralis (FSF) were extracted and purified then characterized by infrared spectroscopy, proton nuclear magnetic resonance spectroscopy and size exclusion chromatography. The results show that BBF and FSF are mainly sulfated with 45.49 and 49.53% (w/w) sulfate, respectively. Analysis of neutral sugars determined by gas chromatography–mass spectrometry showed that FSF and BBF were mainly composed of 64% and 91% fucose and 20% and 6% galactose, respectively, with a few other sugars such as glucose (8% in FSF), rhamnose (1% in BBF) and mannose (8% in FSF and, 2% in BBF). The eliciting activity of these sulfated polysaccharides in stimulating the natural defenses of the date palm was evaluated through the activity of phenylalanine ammonia-lyase (PAL), and the increase in phenols and lignin content in the roots. The results obtained clearly show that the two fucoidans early and intensely stimulate the natural defenses of the date palm after 24 h of treatments. This remarkable elicitor effect seems to be linked to the sulfated groups compared to non-sulfate alginates extracted from the same algae. These results open promising perspectives for a biological control approach against date palm diseases.     

First report of signs of infection by Coccomyxa-like algae in wild blue mussels,Mytilus spp., in the Gulf of Maine (USA,Maine)

In August 2019, visual inspection of intertidal zones of the Gulf of Maine (ME, USA) revealed young and adult wild blue mussels, Mytilus spp., in Alley Bay (Jonesport area) with the distinctive L-shaped shell deformity (LSSD) and green spots (GS) in the mantle and adductor muscle. LSSD is a characteristic sign of current or previous mussel infection by photosynthetic unicellular alga from the group Coccomyxa, while GS are algal colonies. Based on these findings, this study represents the first report of infection signs by pathogenic Coccomyxa-like algae in mussels from the coastal waters of the Northeastern United States, providing a base for future large scale monitoring of the alga in the region.     

Density‐dependent growth and survival in salmonids: Quantifying biological mechanisms and methodological biases

Understanding the complex variation in patterns of density‐dependent individual growth and survival across populations is critical to adaptive fisheries management, but the extent to which this variation is caused by biological or methodological differences is unclear. Consequently, we conducted a correlational meta‐analysis of published literature to investigate the relative importance of methodological and biological predictors on the shape and strength of density‐dependent individual growth and survival in salmonids. We obtained 160 effect sizes from 75 studies of 12 species conducted between 1977 and 2019 that differed in experimental approach (sensu Ecological Monographs, 54, 187–211; 65 laboratory experiments, 60 observational field studies, and 35 field experiments). The experimental approach was the strongest factor influencing the strength of density dependence across studies: density‐dependent survival was stronger than growth in field observational studies, whereas laboratory experiments detected stronger density‐dependent growth than survival. The difference between density‐dependent growth and survival was minimal in field experiments, and between lotic and lentic habitats. The shape of density dependence (logarithmic, linear, exponential or density‐independent) could be predicted with 66.7% accuracy based solely on the experimental approach and the density gradient (highest/lowest*100) of the study. Overall, the strength and shape of density dependence were primarily influenced by methodological predictors, while biological factors (predator presence, food abundance, and species) had predictable but modest effects. For both empirical studies and adaptive fisheries management, we recommend using field experiments with a density gradient of at least 470% to detect the proper shape of the density‐dependent response, or accounting for potential biases if observational or laboratory studies are conducted.