Impact des pseudo-fèces de moules sur les densités des bactéries hétérotrophes dans le secteur mytilicole de la lagune de Bizerte (Tunisie)

Cette étude se propose de caractériser au niveau du secteur mytilicole de la lagune de Bizerte l’impact des pseudo-fèces de moules sur les densités bactériennes, particulièrement celles des Vibrionaceae et des bactéries hétérotrophes. Les prospections ont été réalisées en hiver 2000 et en été 2001 au niveau de 5 stations plus ou moins proches d’une table d’élevage, aussi bien dans la colonne d’eau que dans le sédiment. Sous le parc, les sédiments étant les plus fortement chargés en fraction fine (78-83%) et en carbone organique total (COT) (2,5%), les densités microbiennes étaient élevées (1,82-2,83 • 108 UFC/g de sédiment pour les bactéries hétérotrophes et 2,50-17,32 • 102 UFC/g pour les Vibrionaceae). Une analyse en composantes principales (ACP) montre une étroite relation entre, d’une part, les concentrations bactériennes et, d’autre part, les teneurs en matière organique et plusieurs variables hydrologiques, particulièrement la température, la salinité et l’oxygène dissous.This study aims to characterize the effect of high organic loads, produced by a mussel farm in the Bizerte Lagoon, on the distribution of bacterial densities of, especially, marine heterotrophic bacteria and Vibrionaceae in the water column and in the sediment. Five sites located along a distance gradient from the mussel breeding ground were surveyed during the winter of 2000 and the summer of 2001. Below the mussel farm, the sediment was characterized by high percentages of fine particles (78-83%) and total organic carbon (TOC; 2.5%). Furthermore, this station exhibited high bacterial densities, especially of heterotrophic flora (1.82-2.83 • 108UFC/g) and Vibrionaceae (2.50-17.32 • 102 UFC/g). Principal components analysis revealed a strong relationship among bacterial density, high organic loads and hydrological parameters, particularly temperature, salinity and dissolved oxygen

Metabarcoding free-living marine nematodes using curated 18S and CO1 reference sequence databases for species-level taxonomic assignments

High‐throughput sequencing has the potential to describe biological communities with high efficiency yet comprehensive assessment of diversity with species‐level resolution remains one of the most challenging aspects of metabarcoding studies. We investigated the utility of curated ribosomal and mitochondrial nematode reference sequence databases for determining phylum‐specific species‐level clustering thresholds. We compiled 438 ribosomal and 290 mitochondrial sequences which identified 99% and 94% as the species delineation clustering threshold, respectively. These thresholds were evaluated in HTS data from mock communities containing 39 nematode species as well as environmental samples from Vietnam. We compared the taxonomic description of the mocks generated by two read‐merging and two clustering algorithms and the cluster‐free Dada2 pipeline. Taxonomic assignment with the RDP classifier was assessed under different training sets. Our results showed that 36/39 mock nematode species were identified across the molecular markers (18S: 32, JB2: 19, JB3: 21) in UClust_ref OTUs at their respective clustering thresholds, outperforming UParse_denovo and the commonly used 97% similarity. Dada2 generated the most realistic number of ASVs (18S: 83, JB2: 75, JB3: 82), collectively identifying 30/39 mock species. The ribosomal marker outperformed the mitochondrial markers in terms of species and genus‐level detections for both OTUs and ASVs. The number of taxonomic assignments of OTUs/ASVs was highest when the smallest reference database containing only nematode sequences was used and when sequences were truncated to the respective amplicon length. Overall, OTUs generated more species‐level detections, which were, however, associated with higher error rates compared to ASVs. Genus‐level assignments using ASVs exhibited higher accuracy and lower error rates compared to species‐level assignments, suggesting that this is the most reliable pipeline for rapid assessment of alpha diversity from environmental samples

Are microplastics efficient remediation tools for removing the statin Lipitor? A laboratory experiment with meiobenthic nematodes

IntroductionThe current experiment investigated the multifaceted effects induced by microplastics and the statin Lipitor on marine benthic nematodes.MethodsThe nematodes were exposed to a single polystyrene and polyvinyl chlorides (both at 1 mg.kg-1 Dry Weight) and two Lipitor concentrations (0.1 and 1 mg.l-1), as well as to a mixture of both types of pollutants, for 30 days.ResultsThe results highlighted a significant decrease in the abundance, individual biomass, and diversity of nematodes directly with the addition of polyvinyl chlorides and/or Lipitor. These treatments induced a greater mortality rate among microvores and diatom feeders compared to other feeding types of nematodes.DiscussionThe nematofauna underwent a strong restructuring phase following exposure to microplastics and Lipitor when added alone, leading to the disappearance of sensitive species and their replacement by more tolerant taxa. The toxicity of Lipitor is attenuated by the physical bonding with polystyrene when added to a mixture and has no negative effect on marine nematode species

Investigating Sulforaphane’s anti-virulence and anti-quorum sensing properties against Pseudomonas aeruginosa

BackgroundP. aeruginosa, a significant bacterium, can cause severe illness and resistance to antibiotics. Quorum sensing (QS) systems regulate virulence factors production. Targeting QS could reduce bacteria pathogenicity and prevent antibiotic resistance. Cruciferous vegetables contain sulforaphane, known for its anti-inflammatory, antioxidant, anticancer, and antimicrobial properties.AimWe aimed to examine the inhibitory influences of sulforaphane, at a sub-inhibitory concentration (¼ minimum inhibitory concentration, MIC), on virulence and QS in P. aeruginosa.Materials and methodsThe sulforaphane’s anti-virulence actions at sub-inhibitory concentrations were explored in vitro and in vivo. A sub-MIC concentration of sulforaphane was combined with anti-pseudomonal drugs, and the results of this combination were assessed. The virtual affinity of sulforaphane for the receptors of QS was studied, and its effect on the expression of QS genes was quantified.ResultsSulforaphane significantly decreased the biofilm formation, motility, ability to withstand oxidative stress, and the synthesis of virulence extracellular enzymes such as proteases, hemolysins, and elastase, as well as other virulence factors like pyocyanin. In addition, sulforaphane lessened the severity of P. aeruginosa infection in mice. Sulforaphane reduced the antipseudomonal antibiotics’ MICs when used together, resulting in synergistic effects. The observed anti-virulence impacts were attributed to the ability of sulforaphane to inhibit QS via suppressing the QS genes’ expression.ConclusionSulforaphane shows promise as a potent anti-virulence and anti-QS agent that can be used alongside conventional antimicrobials to manage severe infections effectively. Furthermore, this study paves the way for further investigation of sulforaphane and similar structures as pharmacophores for anti-QS candidates

An experimental protocol to select nematode species from an entire community using progressive sedimentary enrichment.

The purpose of this study was to introduce free-living marine nematodes to the ‘world of biomarkers’.Biomarkers are still not used in the monitoring and assessment of this highly diverse phylum, becausethe technique needs to be applied at the single species level. This incurs high costs and involves time-consuming procedures, which are currently the main pitfalls when it comes to the application of thesetechniques to marine nematodes. Consequently, this work proposes an innovative protocol for selectinga single species from an entire community of nematodes using two independent selection processeswhereby the sediment of the microcosms is progressively and separately enriched with fine and coarsesediment fractions. During our experiment, the abundance and number of nematode species decreaseddiscernibly with exposure to both finer and coarser sediment. Multivariate analyses revealed that deposit-and epigrowth-feeders were the most tolerant feeding guilds, probably due to their deposit-feedingand microvore behaviours. At the end of the experiment, Terschellingia longicaudata and Ptycholaimellusponticus became the unique members of the community when the sediment was enriched with fine andcoarse sediment particles, respectively. After the complete alteration of the community, and when themono-species level had been achieved, it was possible to maintain these two species alive, and withoutany drop in numbers, under the same laboratory conditions considered during the selection process.Accordingly, the protocol adopted here lays new foundations for the study of nematodes in the biomarkerfield

Environmental quality assessment of El Bibane lagoon (Tunisia) using taxonomic and functional diversity of meiofauna and nematodes

The lagoon of El Bibane (Tunisia) is a Mediterranean coastal area that is affected by an increasing human impact. Thus, an estimation of its biodiversity and an ecological quality assessment are very urgent. This study investigates the meiofaunal and nematode communities of the El Bibane lagoon both from a taxonomic and a functional point of view. Nematodes were the dominant group as is common in brackish water systems. The nematode community was made up of 62 genera in 22 families. Xyalidae, Chromadoridae and Cyatholaimidae were the richest and most abundant families. The taxonomic composition and biodiversity of nematodes were comparable to those found in other European and Mediterranean transitional areas. Both meiofauna and nematodes showed a clear subdivision between marginal and central areas. The central stations, represented by fine sediments and higher amounts of organic carbon, seemed to be characterized by low meiofaunal densities, nematode diversity and a strong dominance of 1B and 2B trophic guilds. These trends could be related not only to the grain size and organic load, but also to a possible influence of tidal currents that can transport pollutants in the central area of the lagoon coming from the adjacent coastal areas. Shannon diversity and life strategies are not always in agreement in defining the ecological quality, but an overall worse ecological quality was detected especially at S6. The results of this study are an important starting point for the future monitoring of the potential and actual human impact on the El Bibane area over time

Dual biocontrol potential of the entomopathogenic fungus Akanthomyces muscarius against Thaumetopoea pityocampa and plant pathogenic fungi

Akanthomyces spp. species are known for their capacity to biocontrol of certain insects and plant pathogens; however, their ability to biocontrol the pine processionary (Thaumetopoea pityocampa) and certain phytopathogenic fungi belonging to the genera Fusarium and Curvularia have not been studied before. In this study, a strain from Akanthomyces muscarius was isolated from wheat grains and then identified by morphological and molecular tests. The strain was further studied for its capacity to control Thaumetopoea pityocampa larvae through dose-mortality tests, and its ability to control some phytopathogenic fungi strains of the genera Fusarium and Curvularia was studied through direct confrontation tests. Dose-mortality tests at three concentrations of Akanthomyces muscarius against the first instar larvae revealed a mortality of 92.15% after 11 days for the concentration of 2.3 × 106 conidia.ml−1, with a median lethal concentration of 7.6 x103 conidia.ml1. Our isolate also showed antifungal activity against these phytopathogenic fungi with inhibition rates ranging from 39.61% to 52.94%. Akanthomyces muscarius proved to be a promising biocontrol agent for plant pests and diseases