Estrategias biotecnológicas para el control de diaphorina citri vectror de la bacteria candidatus liberibacter asiaticus, agente causal de huanglongbing.

Tesis (Doctor en Ciencias con acentuación en Química de Productos Naturales) UANL, 2014.

Parasitismo de tamarixia triozae (Burks) (hymenoptera: eulophidae) sobre bacteria cockerelli (sulc.) hemíptera: triozidae) y su interacción con aislamientos del hongo entomopatógeno beauveria bassiana (bálsamo) vuill (ascomycota: hypocreales).

Tesis (Doctor en Ciencias con especialidad en Microbiología) UANL, 2014.

Impacts de la fertilisation phosphatée sur la biodiversité microbienne de sols agricoles

La fertilisation phosphatée est très répandue dans les pratiques agricoles Nord-Américaines. Bien que généralement très efficace pour augmenter la production végétale, son utilisation peut engendrer certaines contaminations environnementales. Afin de diminuer ce problème, plusieurs pratiques de gestion sont envisagées. Parmi celles-ci, on retrouve l’intéressante possibilité de manipuler la flore microbienne car cette dernière est reconnue pour son implication dans bons nombres de processus fondamentaux liés à la fertilité du sol. Cette étude a démontré que lors d’essais en champs, la forme de fertilisant ajouté au sol ainsi que la dose de phosphore (P) appliquée avaient un impact sur la distribution des microorganismes dans les différentes parcelles. Une première expérience menée sur une culture de luzerne en prairie semi-aride a montré que les échantillons provenant de parcelles ayant reçu différentes doses de P présentaient des différences significatives dans leurs communautés bactériennes et fongiques. La communauté de CMA est restée similaire entre les différents traitements. Une deuxième expérience fut menée pendant trois saisons consécutives afin de déterminer l’effet de différentes formes de fertilisation organiques et minérale ajustées selon une dose unique de P sur les populations bactériennes et fongiques d’une culture intensive de maïs en rotation avec du soja. Les résultats des analyses ont montrés que les populations varient selon le type de fertilisation reçu et que les changements sont indépendants du type de végétaux cultivé. Par contre, les populations microbiennes subissent une variation plus marquée au cours de la saison de culture. La technique de DGGE a permis d’observer les changements frappant la diversité microbienne du sol mais n’a permis d’identifier qu’une faible proportion des organismes en cause. Parallèlement à cette deuxième étude, une seconde expérience au même site fut menée sur la communauté de champignons mycorhiziens à arbuscules (CMA) puisqu’il s’agit d’organismes vivant en symbiose mutualiste avec la majorité des plantes et favorisant la nutrition de même que l’augmentation de la résistance aux stress de l’hôte. Ceci permit d’identifier et de comparer les différents CMA présents dans des échantillons de sol et de racines de maïs et soja. Contrairement aux bactéries et aux champignons en général, les CMA présentaient une diversité très stable lors des différents traitements. Par contre, au cours des trois années expérimentales, il a été noté que certains ribotypes étaient significativement plus liés au sol ou aux racines. Finalement, l’ensemble de l’étude a démontré que la fertilisation phosphatée affecte la structure des communautés microbiennes du sol dans les systèmes évalués. Cependant, lors de chaque expérience, la date d’échantillonnage jouait également un rôle prépondérant sur la distribution des organismes. Plusieurs paramètres du sol furent aussi mesurés et ils présentaient aussi une variation au cours de la saison. L’ensemble des interactions possibles entre ces différents paramètres qui, dans certains cas, variaient selon le traitement appliqué, aurait alors probablement plus d’impact sur la biodiversité microbienne que la seule fertilisation.

Beyond Panel Unit Root Tests: Using Multiple Testing to Determine the Non Stationarity Properties of Individual Series in a Panel

Most panel unit root tests are designed to test the joint null hypothesis of a unit root for each individual series in a panel. After a rejection, it will often be of interest to identify which series can be deemed to be stationary and which series can be deemed nonstationary. Researchers will sometimes carry out this classification on the basis of n individual (univariate) unit root tests based on some ad hoc significance level. In this paper, we demonstrate how to use the false discovery rate (FDR) in evaluating I(1)=I(0) classifications based on individual unit root tests when the size of the cross section (n) and time series (T) dimensions are large. We report results from a simulation experiment and illustrate the methods on two data sets.

Diversité des champignons endophytes mycorhiziens et de classe II chez le pois chiche, et influence du génotype de la plante

réalisé en cotutelle avec la Faculté des Sciences de Tunis, Université Tunis El Manar.

Zinc as an agent for the prevention of biofilm formation by pathogenic bacteria

Les biofilms sont des communautés structurées de micro-organismes enrobées dans une matrice extracellulaire. Les biofilms sont impliqués dans la persistance de plusieurs maladies infectieuses et la matrice extracellulaire du biofilm protège les bactéries contre les cellules du système immunitaire de l'hôte, les antibiotiques et les désinfectants. Récemment notre laboratoire a démontré que le zinc inhibe la formation de biofilm chez Actinobacillus pleuropneumoniae, une bactérie pathogène du porc. Le but de cette étude est d'évaluer l'effet du zinc sur la croissance et la formation du biofilm chez différentes bactéries pathogènes du porc, telles que Bordetella bronchiseptica, Escherichia coli, Haemophilus parasuis, Salmonella, Staphylococcus aureus et Streptococcus suis. Les bactéries ont été cultivées dans des plaques de 96 puits sous condition optimale de formation de biofilm et les biofilms ont été colorés au cristal violet. La présence du biofilm a été confirmée par microscopie confocale à balayage laser à l’aide du marqueur fluorescent FilmTracerTM FM ® 1-43. À des concentrations micromolaires, le zinc inhibe faiblement la croissance bactérienne et bloque d'une manière dose-dépendante la formation de biofilm d’A. pleuropneumoniae, Salmonella Typhimurium et H. parasuis. De plus, la formation de biofilm de E. coli, S. aureus et S. suis a été faiblement inhibée par le zinc. Nos résultats indiquent que le zinc a un effet inhibiteur sur la formation de biofilm de la plupart des pathogènes bactériens d'origine porcine. Cependant, le mécanisme sous-jacent de l'activité anti-biofilm du zinc reste à être caractérisé.

Antibody Based Diagnostic for Detection Of Vibrios and their Biological Control using Antagonistic Bacteria in Macrobrachium Rosenbergii Larval Rearing Systems

The main objective of the work undertaken here was to develop an appropriate microbial technology to protect the larvae of M.rosenbergii in hatchery from vibriosis. This technology precisely is consisted of a rapid detection system of vibrios and effective antagonistic probiotics for the management of vibrios. The present work was undertaken with the realizations that to stabilize the production process of commercial hatcheries an appropriate, comprehensive and fool proof technology is required primarily for the rapid detection of Vibrio and subsequently for its management. Nine species of Vibrio have been found to be associated with larvae of M. rosenbergii in hatchery. Haemolytic assay of the Vibrio and Aeromonas on prawn blood agar showed that all isolates of V. alginolyticus and Aeromonas sp., from moribund, necrotized larve were haemolytic and the isolates of V.cholerae, V.splendidus II, V.proteolyticus and V.fluvialis from the larvae obtained from apparently healthy larval rearing systems were non-haemolytic. Hydrolytic enzymes such as lipase, chitinase and gelatinase were widespread amongst the Vibrio and Aeromonas isolates. Dominance of V.alginolyticus among the isolates from necrotic larvae and the failure in isolating them from rearing water strongly suggest that they infect larvae and multiply in the larval body and cause mortality in the hatchery. The observation suggested that the isolate V. alginolyticus was a pathogen to the larvae of M.rosenbergii. To sum up, through this work, nine species of Vibrio and genus Aeromonas associated with M.rosenbergii larval rearing systems could be isolated and segregated based on the haemolytic activity and the antibodies (PA bs) for use in diagnosis or epidemiological studies could be produced, based on a virulent culture of V.alginolyticus. This could possibly replace the conventional biochemical tests for identification. As prophylaxis to vibriosis, four isolates of Micrococcus spp. and an isolate of Pseudomonas sp. could be obtained which could possibly be used as antagonistic probiotics in the larval rearing system of M.rosenbergii.

Polyphosphate Accumulation by Marine Bacteria

Phosphate (Pi) is one among the most important essential residues in maintenance and inheritance of life, with far diverse physiological role as structural, functional and energy transduction. Phosphate accumulation in wastewaters containing run off of fertilizers and industrial discharges is a global problem that results in algal blooms in bays, lakes and waterways. Currently available methods for removing phosphates from wastewater are based primarily on polyP accumulation by the activated sludge bacteria. PolyP plays a critical role in several environmental and biotechnological problems. Possible relation of interaction between polyP accumulation phenomenon, the low biomass, low Pi uptake, and varying results obtained in response to the impact of sodium chloride, pH, temperature, various inorganic salts and additional carbon sources studied, are all intriguing observations in the present investigation. The results of the present study have evidenced very clearly the scope for potential strains of bacteria from both sea water and marine sediments which could be exploited both for Pi removal in wastewater released by industries and intensive aquaculture practices in to the aquatic environment as well as to harness the potential strains for industrial production of polyP which was wide range of applications.

Laser Induced Fluorescence Based Optical Fiber Probe for Analyzing Bacteria

Optical fiber based laser induced fluorescence (LIF) measurements were carried out using Rhodamine B to analyze two different species of bacteria , a Gram-positive bacteria namely Bacillus smithii , and fibrin alginolvticus, a Gram- negative bacteria . The fiber sensor was clearly able to distinguish between the two species of bacteria . Quenching effect of the dye Rhodamine B by Bacillus smithii was observed . The effect of dye on the samples was also studied in detail.

Heterotrophic Bacteria Associated with Healthy and Moribund Larvae of Penaeus monodon H.Milne Edwards

Heterotrophic bacterial flora of Pmonadon from an apparently healthy hatchery system as well as a pool with heavy mortality were isolated and studied. In the healthy systems comparatively higher generic diversity with Pseudomonas, Acinetobacter, Bacillus, Micrococcus, members of the family Enterobacteriaceae and coryneform group in the diminishing order of dominance was recorded. Meanwhile from the moribund larvae and rearing water Aeromonas and Pseudomonas could be isolated in almost equal proportions. Strikingly, Aeromonas could not be isolated from the apparently healthy larval rearing system and its exclusive occurrence in the sick culture system in comparatively higher percentage suggested its possible role in the mortality. They were found to be highly halophilic exhibiting growth at 10% NaCl. On testing their sensitivity to twenty antibiotics, four of them (Streptomycin, Gentamycin, Methamine mandelate and Cloramphenicol) were found to be effective on all the isolates of Aeromonas and Pseudomonas suggesting their possible application in the hatchery system in times of emergency. While doing so, Streptomycin would do comparatively better than the others as the minimum inhibitory dose required was comparatively lower (200ppm) within a period of 24 hours

Phosphatases from Bacteria Isolated from the Arabian Sea and Cochin Estuary

This study aims to reveal the ability of bacteria isolated from Cochin estuary and the Arabian Sea to produce phosphatases, important characters of the enzymes, its ability to utilize organophosphorus compounds as source of phosphate and also their role in degradation of organophosphorus pesticides. It deals with isolation, identification and screening of bacteria for phosphatase production, and it describes the effect of cultural conditions on growth and phosphatase production. The effect of various factors like pH, NaCl concentration, temperature of incubation, carbon source, period of incubation etc. on growth and phosphatase production by the two selected species were studied to establish suitable environment for phosphatase production by these bacteria. In this study regulation of phosphatase synthesis, characteristics of acid and alkaline phosphatases are discussed.

Laser induced fluorescence based optical fiber probe for analyzing bacteria

Optical fiber based laser induced fluorescence (LIF) measurements were carried out using Rhodamine B to analyze two different species of bacteria , a Gram-positive bacteria namely Bacillus .cmithii , and fibrin alginolvticus, a Gram-' negative bacteria . The fiber sensor was clearly able to distinguish between the two species of bacteria . Quenching effect of the dye Rhodamine B by Bacillus smitltii was observed . The effect of dye on the samples was also studied in detail.