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

Biodiversité des bactéries halophiles de Chotts et Sebkhas tunisiens et applications biotechnologiques

Les bactéries halophiles (modérées et extrêmes) ont été isolées à partir de sites hypersalins tels que les lacs et les sols salés aussi bien que des lacs alcalins. La biodiversité taxonomique des microorganismes trouvés dans les environnements hypersalés, est liée essentiellement à la haute concentration en sel. Les microorganismes halophiles sont doués d une activité métabolique et physiologique intervenant dans la fermentation d aliments ainsi que dans la transformation et la dégradation des déchets et des polluants organiques des environnements salés. Les bactéries halophiles sont classées parmi les microorganismes modérés dont la concentration du milieu en NaCl se situe entre 0,5 M et 2,5 M alors que les bactéries extrêmophiles poussent dans des milieux où la salinité est supérieure à cette concentration. La diversité microbienne dans les écosystèmes hypersalins au nord et au sud de la Tunisie a été faiblement étudiée. Chott El-Djerid et Sebkhas Sehline, les deux grands lacs salés du pays représentent les sources les plus importantes du sel de cuisine. L intêret économique de ces régions nous amène à une étude taxonomique des microorganismes qui occupent de tels écosystèmes. L objectif de ce travail est d examiner par des approches phénotypiques, physiologiques, biochimiques et moléculaires, les souches isolées à partir des deux environnements ainsi que d étudier les caractéristiques de ces souches nouvelles. Les isolats étudiés sont repiqués sur milieu concentré en sel (25% NaCl). La caractérisation moléculaire a été effectuée et les résultats obtenus montrent que les isolats représentatifs de la collection sont des bactéries aérobies appartenant phylogénétiquement aux genres Salicola, Pontibacillus, Bacillus, Halomonas, Marinococcus, Yeomjeonicoccus, Gracilibacillus, Halovibrio, Pseudomonas et Halobacillus. Dans les conditions d anaérobiose de Chott El-Djerid, une seule bactérie a été isolée. L identification moléculaire de cette souche et la comparaison phylogénétique avec les plus proches, montrent que la souche 6SANG représente une nouvelle espèces d un nouveau genre Halanaerobaculum tunisiense gen. nov., sp. nov. Pour confirmer la biodiversité des espèces fongiques des sites hypersalés de Sebkha Sehline, une analyse moléculaire a été réalisée pour les neuf isolats grâce à un séquençage du gène ITS. Les résultats témoignent de la présence de quatre espèces différents et qui sont : Hypocrea lixii, Hypocrea koningii, Trichoderma longibrachiatum et Pichia guilliermondii.Hypersaline environments are found in a wide variety of aquatic and terrestrial ecosystems. Bacterial aerobic communities were recovered from sediments of the shallow salt lake of the hypersalins environments and their distribution with respect to salinity gradients was established. The north and south of Tunisia consists of numerous ecosystems including extreme environments in which the microbial diversity has not been studied. We isolated the bacterial and archaeal communities in the shallow salt lake (El-Djerid and Sebkhas) and their distribution with respect to different physico-chemical characteristics like salinity gradients was established. The characterization was performed by using phenotypic characters including morphological, physiological, biochemical, nutritional test and phylogenetic approaches. Due to the economic importance of salt obtained from this lake, a microbial survey has been conducted. Physico-chemical analysis showed that the salts contain sufficient ions and hardness to support extremely halophilic bacteria. The salt collected from the lake contained a microbial community well adapted to the specific physical and nutritional conditions of each site. The results of analyses were quite similar and demonstrated the phenotypic heterogeneity of the species in question. Extreme bacteria were recovered from sampling sites, which contained up to 250 g/l NaCl. Results of this study were discussed with regard to the ecological significance of these microorganisms in the breakdown of organic matter in hypersalins environments together with the potential use of them in the industry. The purpose of this research was to examine their phenotypic features and their physiological and biochemical characteristics with the aim to screen for metabolites of industrial interest produced by the novel halophilic isolates. A new halophilic anaerobe was isolated from the hypersaline surface sediments of El-Djerid Chott, Tunisia. The isolate, designated as strain 6SANG, grew at NaCl concentrations ranging from 14 to 30%. Based on phenotypic and phylogenetic characteristics, we propose that this bacterium be classified as a novel species of a novel genus, Halanaerobaculum.AIX-MARSEILLE1-BU Sci.St Charles (130552104) / SudocSudocFranceF

Characterization of a novel chitinase from a moderately halophilic bacterium, Virgibacillus marismortui strain M3-23

A new chitinase produced by the moderately halophilic bacterium Virgibacillus marismortui strain M3- 23 was identified and characterized. Distinguishable characteristics of high activity and stability at different pH, temperatures and salinity of M3-23 chitinase are reported. Analysis of the catalytic domain sequence from the enzyme highlighted its relationship to glycosyl hydrolase family 18. Comparison of the deduced chitinase sequence from strain M3-23 to known chitinases from Bacillus species showed low similarity (82%), suggested its novelty. This is the first report of the characterization of chitinase from the species V. marismortui. The halo- and thermo-tolerant nature of the chitinolytic enzyme allows its potential use in agricultural and industrial applications