Studies on the Biodiversity of Halophilic Microorganisms Isolated from El-Djerid Salt Lake (Tunisia) under Aerobic Conditions

Bacterial and archaeal aerobic communities were recovered from sediments from the shallow El-Djerid salt lake in Tunisia, and their salinity gradient distribution was established. Six samples for physicochemical and microbiological analyses were obtained from 6 saline sites in the lake for physico-chemical and microbiological analyses. All samples studied were considered hypersaline with NaCl concentration ranging from 150 to 260 g/L. A specific halophilic microbial community was recovered from each site, and characterization of isolated microorganisms was performed via both phenotypic and phylogenetic approaches. Only one extreme halophilic organism, domain Archaea, was isolated from site 4 only, whereas organisms in the domain Bacteria were recovered from the five remaining sampling sites that contained up to 250 g/L NaCl. Members of the domain Bacteria belonged to genera Salicola, Pontibacillus, Halomonas, Marinococcus, and Halobacillus, whereas the only member of domain Archaea isolated belonged to the genus Halorubrum. The results of this study are discussed in terms of the ecological significance of these microorganisms in the breakdown of organic matter in Lake El-Djerid and their potential for industry applications

Diarrheagenic Escherichia coli pathotypes isolated from children with diarrhea in the Federal Capital Territory Abuja, Nigeria

International audienceIntroduction: Escherichia coli are frequently isolated from diarrheic children in the Federal Capital Territory Abuja, Nigeria, but their virulent properties are not routinely evaluated. Therefore, the etiology of childhood diarrheal disease attributable to diarrheagenic Escherichia coli (DEC) in Abuja, Nigeria remains unknown. Methodology: Stool specimens from 400 acute diarrheic children between 0 and 60 months of age were studied. E. coli strains isolated were evaluated by polymerase chain reaction (PCR) for nine virulence genes and HEp-2 cell adherence to detect and identify five distinct diarrheagenic E. coli categories. Results: Diarrheagenic E. coli was detected in 51 (12.8%) of the diarrheic children. The observed DEC pathotypes were enteropathogenic E. coli (EPEC) in 18 (4.5%) children, enterotoxigenic E. coli (ETEC) in 16 (4.0%), enteroaggrative E. coli (EAEC) in 8 (2.0%), enterohaemorrhagic E. coli (EHEC) in 6 (1.5%), and enteroinvasive E. coli (EIEC) in 3 (0.8%). Four (1.0 %) EPEC strains with only the eae+ gene that adhered diffusely to HEp-2 cell were identified as atypical EPEC. All the DEC categories except atypical EPEC were identified in children between 6 and 12 months of age. Conclusions: This study underscores the need for routine evaluation of diarrheic children for virulence properties of infectious DEC. Atypical EPEC are emerging among the DEC pathotypes isolated from childhood acute gastroenteritis in Abuja, Nigeria

Étude de l’influence des facteurs environnementaux sur la distribution de différentes populations bactériennes dans une station mytilicole de la lagune de Bizerte (Nord-Tunisie)

La présente étude a été effectuée en vue d’évaluer l’effet des fluctuations des paramètres abiotiques sur la distribution de différentes populations bactériennes viables dans la station mytilicole la plus productrice de la lagune de Bizerte (Nord‑Tunisie). Le suivi a été établi pendant une année (septembre 2004 ‑ août 2005) au niveau des neuf tables du site.Les dénombrements bactériens des coliformes totaux (CT), des entérocoques fécaux (EF), des Vibrionaceaes (VB) et des bactéries hétérotrophes cultivables (BHC) ont été effectués pour l’eau de surface, les moules (Mytilus galloprovincialis) ainsi que pour les sédiments. Ces charges bactériennes ont été corrélées à la température de l’eau, l’oxygène dissous, la salinité, le pH, la pluviométrie et l’ensoleillement, mesurés périodiquement en tout point du site.Le suivi des paramètres bactériologiques a révélé une présence assez importante de charges bactériennes pendant toute la période d’étude, notamment dans les moules et les sédiments, avec une distribution temporelle saisonnière. L’étude statistique a montré des corrélations positives, d’une part, entre les charges en polluants fécaux et la pluviométrie et, d’autre part, entre les charges en Vibrionaceaes et la salinité et la température.Ces résultats révèlent l’effet anthropique bactérien au niveau du site mytilicole : les rejets continentaux en hiver et la remontée des bactéries autochtones en période estivale ont une influence considérable sur la mytiliculture et son devenir dans la lagune de Bizerte.The present study aimed to assess the influence of abiotic parameters on the distribution of various viable bacterial populations in the most productive mussel farming area in the Bizerte Lagoon (Northern Tunisia). A monitoring survey was carried out over one year (September 2004 ‑ August 2005), within all the farming tables at the station. Bacterial enumerations of total coliforms (CT), fecal enterococci (EF), Vibrionaceae (VB) and cultivable heterotrophic bacteria (BHC) were carried out for surface water, mussels (Mytilus galloprovincialis) and sediments. These bacterial counts were correlated with water temperature, dissolved oxygen, salinity, pH, rainfall and sunshine, which were periodically measured at all points within the sampling area.The survey of the bacteriological parameters revealed high bacterial counts during the whole monitoring period, especially in the mussels and sediments, as well as seasonal variability. Statistical analyses revealed positive correlation between the loads of fecal pollutants and rainfall during the winter period, and between the loads of Vibrionaceae and salinity and temperature during the summer period.These results highlight the negative anthropogenic bacterial effect within the mussel farming areas: sewage discharges in winter, and the growth of autochthonous pathogenic bacteria during the summer period, have a considerable influence on the mussel culture in the Bizerte Lagoon

Antibiotic resistance and virulence of faecal enterococci isolated from food-producing animals in Tunisia

Antimicrobial agents exert a selection pressure not only on pathogenic, but also on commensal bacteria of the intestinal tract of humans and animals. The aim of this work was to determine the occurrence of different enterococcal species and to analyse the prevalence of antimicrobial resistance and the mechanisms implicated, as well as the genetic diversity in enterococci recovered from faecal samples of food-producing animals (poultry, beef and sheep) in Tunisia. Antimicrobial resistance and the mechanisms implicated were studied in 87 enterococci recovered from 96 faecal samples from animals of Tunisian farms. Enterococcus faecium was the most prevalent species detected (46 %), followed by E. hirae (33.5 %). High percentages of resistance to erythromycin and tetracycline were found among our isolates, and lower percentages to aminoglycosides and ciprofloxacin were identified. Most of the tetracycline-resistant isolates carried the tet(M) and/or tet(L) genes. The erm(B) gene was detected in all erythromycin-resistant isolates. The ant(6)-Ia, aph(3)-Ia and aac(6)-aph(2) genes were detected in nine aminoglycoside-resistant isolates. Of our isolates, 11.5 % carried the gelE gene and exhibited gelatinase acitivity. The esp gene was detected in 10 % of our isolates and the hyl gene was not present in any isolate. The predominant species (E. faecium and E. hirae) showed a high genetic diversity by repetitive extragenic palindromic (REP)-PCR. Food animals might play a role in the spread through the food chain of enterococci with virulence and resistance traits to humans. © 2014 Springer-Verlag Berlin Heidelberg and the University of Milan

Aridity modulates belowground bacterial community dynamics in olive tree

Aridity negatively affects the diversity and abundance of edaphic microbial communities and their multiple ecosystem services, ultimately impacting vegetation productivity and biotic interactions. Investigation about how plant-associated microbial communities respond to increasing aridity is of particular importance, especially in light of the global climate change predictions. To assess the effect of aridity on plant associated bacterial communities, we investigated the diversity and co-occurrence of bacteria associated with the bulk soil and the root system of olive trees cultivated in orchards located in higher, middle and lower arid regions of Tunisia. The results indicated that the selective process mediated by the plant root system is amplified with the increment of aridity, defining distinct bacterial communities, dominated by aridity-winner and aridity-loser bacteria negatively and positively correlated with increasing annual rainfall, respectively. Aridity regulated also the co-occurrence interactions among bacteria by determining specific modules enriched with one of the two categories (aridity-winners or aridity-losers), which included bacteria with multiple PGP functions against aridity. Our findings provide new insights into the process of bacterial assembly and interactions with the host plant in response to aridity, contributing to understand how the increasing aridity predicted by climate changes may affect the resilience of the plant holobiont

Production and partial characterization of chitinase from a halotolerant Planococcus rifitoensis strain M2-26

peer reviewedThis paper is the first to investigate the production and partial characterization of the chitinase enzyme from a moderately halophilic bacterium Planococcus rifitoensis strain M2-26, earlier isolated from a shallow salt lake in Tunisia. The impact of salt, salinity concentration, pH, carbon and nitrogen sources on chitinase production and activity have been determined. This is the first report on a high salt-tolerant chitinase from P. rifitoensis, since it was active at high salinity (from 5 to 30% NaCl) as well as in the absence of salt. This enzyme showed optimal activity at 70 C and retained up to 82 and 66% of its original activity at 80 or 90 C, respectively. The activity of the enzyme was also shown over a wide pH range (from 5 to 11). For characterization of the enzyme activity, the chitinase secreted in the culture supernatant was partially purified. The preliminary study of the concentrated dialysed supernatant on native PAGE showed at least three chitinases produced by strain M2-26, with highest activity approximately at 65 kDa. Thus, the thermo-tolerant and high salt-tolerant chitinases produced by P. rifitoensis strain M2-26 could be useful for application in diverse areas such as biotechnology and agro-industry

Enhancing Bioinformatics and Genomics Courses: Building Capacity and Skills via Lab Meeting Activities: Fostering a Culture of Critical Capacities to Read, Write, Communicate and Engagein Rigorous Scientific Exchanges

Publié dans BioEssays, 2020, 42(10), 2000134International audienceReading, writing, publishing, and publicly presenting scientific works are vital for a young researcher's profile building and career development. Generally, the traditional educational curricula do not offer training possibilities to learn and practice how to prepare, write, and present scientific works. These are rather a part of lab meeting activities in research groups. The lack of such training is more critical in some developing countries because this adds to the rare opportunities to discuss and become involved in the exchanges on state of the art scientific literature. Here the authors relate their experience in introducing a weekly 1-day lab meeting in the framework of two previously organized 3-month courses on "Bioinformatics and Genome Analyses". The main activities which are developed during these lab meetings include scientific literature follow up as well as preparing and presenting oral and written scientific reviews. These activities prove to be useful for a student's self-confidence building, for enhancing their active participation during the lectures and practical sessions, as well as for the positive impact on running the whole course program. Incorporation of such lab meeting activities in the course program significantly improves the capacity building of the participants, their analytical and critical reading of scientific literature, as well as communication skills. In this work it is shown how to proceed with the different steps involved in the implementation of lab meeting activities, and to recommend their regular institution in similar courses. Lab meetings are at the heart of scientific life because they provide an exceptional environment for developing skills in team work, networking, exchange on research advances and for enhancing self-confidence and career-building by offering young researchers opportunities to learn how to 1) prepare and present personal research findings ; 2) select and discuss challenging papers ; 3) develop and hone analytical skills; 4) practice communication skills. We adapted this concept by incorporating a weekly 1-day lab meeting in the organization of two 3-month "Bioinformat-ics and Genome Analyses" courses [1] that we organized at the Institut Pasteur Tu-nis, Tunisia. The course was intended for about twenty selected young Ph.D. students and researchers with backgrounds in Biology , Mathematics, Statistics or Computer Science. It was focused on topics related to bioinformatics, comparative genomics, metagenomics, genome variant analyses and programming in a Unix environment. In order to foster the participants' involvement in the lab meeting activities, each participant had to prepare a synthetic review based on some selected bib-liographic resources. This "bibliographic project" constituted a significant component of the course outcome, and had to be formally presented at the end of the course. For that purpose, a large number of quality published papers encompassing most of the course topics were specifically collected and passed to the participants. These documents helped the participants to follow the course program and to select adequate papers for their respective projects. Central activities during lab meetings included work toward preparation of the different projects, follow-up of recent scientific literature, critical reading of papers, review preparation, and presentation, as well as idea-sharing through discussion. Figure 1 shows the steps that we followed in the development of activities. Four main operational objectives constituted the backbone of the procedure implementing these activities 1) Training on reading scientific literature; 2) Preparation of oral presentation and synthetic reviews; 3) Organizing and leading lab meetings; 4) Final review presentation and evaluation. In the following we develop the content of these activities and introduce their implementation in the context of the course program

L' entomophathogène Bacillus thuringiensis (identification d'un nouveau sérovar, persistance des spores et implication des métalloprotéases dans le pouvoir pathogène)

PARIS7-Bibliothèque centrale (751132105) / SudocSudocFranceF

Développement d'outils génétiques pour identifier les facteurs de virulence chez Vibrio tapetis, un vibrio pathogène de palourde

Les travaux de cette thèse ont porté sur le développement d outils génétiques pour l étude de Vibrio tapetis, l agent étiologique de la maladie de l anneau brun chez la palourde Ruditapes philippinarum. L acquisition de ces outils a ainsi permis de caractériser djlA, un gène qui code pour une protéine chaperon membranaire de la famille de DnaJ/ Hsp40. L analyse du locus de djlA chez V. tapetis a révélé une organisation putative en opéron: en aval de djlA on trouve un gène Vt-duf924, codant pour une protéine de fonction inconnue. Il a été également montré l importance de djlA dans la virulence chez V. tapetis. Par ailleurs, un plasmide pVT1 de 82,3 kb a été isolé à partir de la souche V. tapetis CECT 4600. pVT1 présente une structure en mosaïque et contient également un grand nombre d éléments mobiles. Ainsi, l analyse de pVT1 souligne l importance des transferts horizontaux et le rôle de navette que jouent les plasmides dans l acquisition de nouvelles ressources génétiques, parmi des bactéries partageant un même environnement. De plus, une caractérisation taxonomique basée sur une approche biochimique et de séquençage de l ADN 16S a été menée sur une collection de souches Vibrio isolées de palourdes sains ou subissant des épisodes de mortalités en Tunisie. Il a été montré que la plupart des souches appartiennent au groupe des V. splendidus. La virulence de trois de ces souches a été étudiée in vivo et in vitro. Ces souches ne semblent pas virulentes. L ensemble des résultats obtenus ouvrent de nombreuses perspectives de recherche dans la compréhension des bases moléculaires de la virulence de V. tapetis et vers une meilleure compréhension des interactions hôte-pathogène.ORSAY-PARIS 11-BU Sciences (914712101) / SudocSudocFranceF