Alterins Produced by Oyster-Associated Pseudoalteromonas Are Antibacterial Cyclolipopeptides with LPS-Binding Activity

Discovery after discovery, host-associated microbiota reveal a growing list of positive effects on host homeostasis by contributing to host nutrition, improving hosts’ immune systems and protecting hosts against pathogens. In that context, a collection of oyster associated bacteria producing antibacterial compounds have been established to evaluate their role in non-host-derived immunity. Here, we described alterins; potent anti-Gram negative compounds produced by Pseudoalteromonas hCg-6 and hCg-42 isolated from different healthy oyster hemolymph. The strains hCg-6 and hCg-42 produce a set of at least seven antibacterial compounds, ranging from 926 to 982 Da structurally characterized as cyclolipopeptides (CLPs). Alterins share the same cationic heptapeptidic cycle connected via an amido bond to different hydrophobic hydrocarbon tails. Their MICs disclosed a potent antibacterial activity directed against Gram-negative bacteria including oyster and human pathogens that may confer a beneficial defense mechanism to the host but also represents an untapped source of new antibiotics. The alterins’ mechanisms of action have been deciphered: after binding to lipopolysaccharides (LPS), alterins provoke a membrane depolarization and permeabilization leading to bacterial lysis. As hCg-6 and hCg-42 produced a set of natural derivatives, the structure/activity relationship linked to the carbon tail is clarified. We showed that the hydrocarbon tail determines the LPS-binding properties of alterins and consequently their antibacterial activities. Its length and saturation seem to play a major role in this interaction.     

Correlations and variance among species traits explain contrasting impacts of fragmentation and habitat loss on functional diversity

Landscape Ecology - Understanding how landscape fragmentation affects functional diversity, defined as the distribution of functional traits in an assemblage, is critical for managing landscapes...     

Absence of oxysterol-like side effects in human monocytic cells treated with phytosterols and oxyphytosterols

Oxysterols, found in some commonly consumed foods, can induce a wide range of cytotoxic effects, which have been extensively studied. On the other hand, the side effects of phytosterols and oxyphytosterols are less well-known. Over the past few years, different types of foods have been enriched with phytosterols on the basis of the properties of these compounds that reduce circulating cholesterol levels in certain experimental conditions. It is therefore important to gain better knowledge of the risks and benefits of this type of diet. In this study, conducted in human monocytic U937 cells, the ability of phytosterols (sitosterol, campesterol) and oxyphytosterols (7β-hydroxysitosterol, 7-ketositosterol) to induce cell death, polar lipid accumulation, and pro-inflammatory cytokine (MCP-1; IL-8) secretion was determined and compared to that of oxysterols (7-ketocholesterol, 7β-hydroxycholesterol). Phytosterols and oxyphytosterols had no significant effects on the parameters studied; only 7β-hydroxysitosterol slightly increased cell death, whereas at the concentration used (20 μg/mL), strong cytotoxic effects were observed with the oxysterols. With sitosterol, campesterol, and 7-ketositosterol, IL-8 secretion was decreased, and with campesterol the intracellular polar lipid level was reduced. The data show that phytosterols and oxyphytosterols have no oxysterol-like side effects, and they rather argue in favor of phytosterols' beneficial effects.     

Influence of the allelic variants encoded at the Gli-B1 locus, responsible for a major allergen of wheat, on IgE reactivity for patients suffering from food allergy to wheat

Wheat presents an important genetic diversity that could be useful to look for cultivars with reduced allergencity. omega5-Gliadins have been described as major allergens for wheat allergic patients suffering from wheat-dependent exercise-induced anaphylaxis (WDEIA) and some cases of chronic urticaria (U). Our objective was to study the influence of genetic variability at the Gli-B1 locus encoding for omega5-gliadins on the reactivity of IgE antibodies from these patients. We selected cultivars expressing 13 alleles at Gli-B1 including a wheat/rye translocation and studied the reactivity to gliadins of a rabbit antiserum specific for omega5-gliadins and of IgE from 10 patients. The antiserum and IgE from nine patients with WDEIA and U strongly detected omega5-gliadins expressed by most of the Gli-B1 alleles but showed no or faint responses to the gliadins and secalins extracted from the translocated wheat. The selection of genotypes lacking the Gli-B1 locus may reduce wheat allergenicity.     

Proteome changes in leaves from grapevine (Vitis vinifera L.) transformed for alcohol dehydrogenase activity

A proteomic approach has been used to study changes in leaf protein content from plants transformed for alcohol dehydrogenase (ADH) activity. Individual quantitative analysis of 190-436 spots separated by two-dimensional electrophoresis was performed, and spots displaying significant quantitative changes between control (C), sense (S), and antisense (R) transformants were selected using Student's t test. Of the 14 spots selected and further analyzed after trypsic digestion, 9 could be identified by MS analysis and 5 by LC-MS/MS. Identified proteins had mainly a chloroplastic origin: four rubisco large subunits, one rubisco binding protein, two glutamine synthetases, one elongation factor Tu, one ATP synthase beta subunit, and one plastidic aldolase. Proteins with other localization were also identified, such as a UDP-glucose pyrophosphorylase, a mitochondrial aminomethyltransferase, a linalool synthase, which comigrated with the protein identified as elongation factor Tu, an enolase comigrating with a glyceraldehyde 3-phosphate dehydrogenase, and a mixture of eight proteins among which were a dehydroascorbate reductase, a chalcone isomerase, and a rubisco activase. The results emphasize the changes in carbon metabolism-associated proteins linked to the alteration in ADH activity of grapevine transformant leaves.     

Occurrence of High In-Stream Nitrite Levels in a Temperate Region Agricultural Watershed

This study is the first to report nitrite occurrence and variability in surface water across an agricultural watershed in the province of Quebec, Canada. Nitrite (NO₂ ^?) concentrations were monitored across a 2.4 km² watershed during 2 years. Water samples were collected at the outlet from April to November and in three contrasted stream branches (six stations) during three hydrological regimes (summer low water levels, fall recharge, and snowmelt). Our study clearly demonstrates that NO₂ ^? levels observed at the outlet are not representative of NO₂ ^? variability across the micro-watershed. Surface water collected in cropped areas presents high NO₂ ^? concentrations during summer low water levels, often exceeding guidelines for aquatic life, with NO₂ ^? means ranging from 0.022 to 0.107 mg N L^?1 and maximum value reaching 0.156 mg N L^?1. Furthermore, the two stream branches in cropped area have demonstrated significant differences in NO₂ ^? concentrations and other water quality parameters. The importance of groundwater discharge to streams in the micro-watershed Bras d’Henri may potentially generate different in-stream sources of NO₂ ^? and water quality parameters. However, further studies are essential to determine sources and processes related to in-stream NO₂ ^? peaks.     

Host cell invasion by apicomplexan parasites: insights from the co-structure of AMA1 with a RON2 peptide

Apicomplexan parasites such as Toxoplasma gondii and Plasmodium species actively invade host cells through a moving junction (MJ) complex assembled at the parasite-host cell interface. MJ assembly is initiated by injection of parasite rhoptry neck proteins (RONs) into the host cell, where RON2 spans the membrane and functions as a receptor for apical membrane antigen 1 (AMA1) on the parasite. We have determined the structure of TgAMA1 complexed with a RON2 peptide at 1.95 angstrom resolution. A stepwise assembly mechanism results in an extensive buried surface area, enabling the MJ complex to resist the mechanical forces encountered during host cell invasion. Besides providing insights into host cell invasion by apicomplexan parasites, the structure offers a basis for designing therapeutics targeting these global pathogens.     

Abundance,perceptions and utilizations of termite mounds in Cambodia

In the Lower Mekong Basin, paddy fields often appear as mosaics, with soil mounds covered by trees or other plants in a spotty distribution. These soil mounds are commonly named termite ‘lenticular mounds’ because termite bioturbation is considered to be at their origin. Termite mounds host a large diversity of animals and plants, increasing landscape patchiness. Because the preservation of these islands of biodiversity is threatened by modern agricultural practices, the aim of this study was to quantify their abundance and the services they provide to the local population. The abundance of mounds and their use by the population were quantified in a catchment in Cambodia. We found that mounds density reached ~2 mounds ha⁻¹. Interviews carried out within the catchment showed that most of the interviewees used mounds for increasing the fertility of their field and for the cultivation of rice and other plants (e.g. sponge gourd and pumpkin). In addition to their potential to increase plant productivity, the survey revealed that animals (rats and snakes), mushrooms and 13 plant species found on or in mounds were consumed by the population. In addition to potentially contributing to an increase in food diversity, mounds also impacted farmers' health by allowing access to 20 medicinal plant species and indirectly via a reduction in pesticide use. In conclusion, this study is the first attempt to quantify the large number of services provided by termite mounds in Cambodia. This increase in the knowledge of the diversity of environmental and socioeconomic services provided by termite mounds is likely to contribute to their preservation and provide a basis for the sustainable management of biodiversity in paddy fields in the Lower Mekong Basin region.