Yeast Biomass: An Alternative for Bioremediation of Heavy Metals

Heavy metal pollution has become one of the most serious environmental problems throughout the world. Among the innovative solutions for treatment of contaminated water and soil, bioremediation that use biological materials like living or dead microorganisms is a promising, safe and economical technology. One of the most ubiquitous biomass types available for bioremediation of heavy metals is yeast. Yeast cells represent an inexpensive, readily available source of biomass that retains its removal ability for a broad range of heavy metals to varying degrees. Furthermore, yeasts exhibit the ability to adapt to extreme conditions such as temperature, pH and high levels of organic and inorganic contaminants. To understand the different mechanisms of interactions between metals and yeast strains in the environment, this paper will give an overview on the role that yeasts play in the immobilization/mobilization of toxic metals and factors affecting these processes. Biotechnological applications in the bioremediation of heavy metal such as bioaugmentation using degradation abilities of yeasts will also be discussed

Correlation between cell surface physicochemical properties of bacterial strains and their chromium removal potential

Physicochemical characterization of microbes has gained recently a great interest by scientific community. It is proved of extreme importance in several fields of science and technology applications such as bioremediation. In this work, we investigated the establishment of a possible correlation between chromium removal capacity of seven bacterial strains isolated from contaminated sites with industrial wastes including tanning processing and their cell surface physicochemical properties. Thus, hydrophobicity and donor/acceptor electrons character were obtained using contact angle measurements. Statistical analysis showed a high significant positive correlation between hexavalent chromium (Cr(VI)) removal by the strains and their acceptor electron character γ+(r = 0.90). While significant negative correlation between the Cr(VI) removal potential and the ΔGiwi value (r = −0.844) and also with their donor electron character γ− (r = −0.746) were observed. These results may contribute to determine a selectrion criteria of bacteria that can be operated in bioremediation applications

A Model for the Development of the Rhizobial and Arbuscular Mycorrhizal Symbioses in Legumes and Its Use to Understand the Roles of Ethylene in the Establishment of these two Symbioses

We propose a model depicting the development of nodulation and arbuscular mycorrhizae. Both processes are dissected into many steps, using Pisum sativum L. nodulation mutants as a guideline. For nodulation, we distinguish two main developmental programs, one epidermal and one cortical. Whereas Nod factors alone affect the cortical program, bacteria are required to trigger the epidermal events. We propose that the two programs of the rhizobial symbiosis evolved separately and that, over time, they came to function together. The distinction between these two programs does not exist for arbuscular mycorrhizae development despite events occurring in both root tissues. Mutations that affect both symbioses are restricted to the epidermal program. We propose here sites of action and potential roles for ethylene during the formation of the two symbioses with a specific hypothesis for nodule organogenesis. Assuming the epidermis does not make ethylene, the microsymbionts probably first encounter a regulatory level of ethylene at the epidermis–outermost cortical cell layer interface. Depending on the hormone concentrations there, infection will either progress or be blocked. In the former case, ethylene affects the cortex cytoskeleton, allowing reorganization that facilitates infection; in the latter case, ethylene acts on several enzymes that interfere with infection thread growth, causing it to abort. Throughout this review, the difficulty of generalizing the roles of ethylene is emphasized and numerous examples are given to demonstrate the diversity that exists in plants

The regulation of arbuscular mycorrhizal symbiosis by phosphate in pea involves early and systemic signalling events

Most plants form root symbioses with arbuscular mycorrhizal (AM) fungi, which provide them with phosphate and other nutrients. High soil phosphate levels are known to affect AM symbiosis negatively, but the underlying mechanisms are not understood. This report describes experimental conditions which triggered a novel mycorrhizal phenotype under high phosphate supply: the interaction between pea and two different AM fungi was almost completely abolished at a very early stage, prior to the formation of hyphopodia. As demonstrated by split-root experiments, down-regulation of AM symbiosis occurred at least partly in response to plant-derived signals. Early signalling events were examined with a focus on strigolactones, compounds which stimulate pre-symbiotic fungal growth and metabolism. Strigolactones were also recently identified as novel plant hormones contributing to the control of shoot branching. Root exudates of plants grown under high phosphate lost their ability to stimulate AM fungi and lacked strigolactones. In addition, a systemic down-regulation of strigolactone release by high phosphate supply was demonstrated using split-root systems. Nevertheless, supplementation with exogenous strigolactones failed to restore root colonization under high phosphate. This observation does not exclude a contribution of strigolactones to the regulation of AM symbiosis by phosphate, but indicates that they are not the only factor involved. Together, the results suggest the existence of additional early signals that may control the differentiation of hyphopodia

Caractérisation, étude thermodynamique et structurale de complexes tétraazamacrocycliques porteurs de groupements pyridine ou pyrazine

L objectif poursuivi au cours de ce travail est l étude de l influence des paramètres structuraux de complexes mono- et bistétraazamacrocycles de cuivre et de nickel sur leurs propriétés électroniques. Les ligands développés dans ce but sont des cyclens et cyclams monoN-fonctionnalisés par des groupements de type pyridine ou des bismacrocycles basés sur des cavités cyclen ou cyclam séparées par des liens de type pyridine ou pyrazine. L influence de la présence d atomes coordinants exomacrocycliques sur les caractéristiques stéréochimiques et électroniques des complexes a ainsi e té évaluée. Dans le cas des complexes de cyclen- et cyclam-pyridine, l analyse radiocristallographique a permis de mettre en évidence que la sphère de coordination du métal comprend l atome d azote pyridinique. Dans le cas du ligand cyclam-méthylpyridine, la synthèse des complexes de nickel et de cuivre a permis d isoler dans chaque cas deux isomères configurationnels. Leur étude électrochimique a permis de montrer que l oxydation (pour le nickel) ou la réduction (pour le cuivre) du métal s accompagne d une isomérisation d un isomère configurationnel en l autre. Ces réarrangements topologiques ne sont possibles que grâce à la modification de degré d oxydation de métal. Dans le cas des complexes bismacrocycliques, l analyse radiocristallographique des complexes, lorsqu elle a été possible, montre que les atomes d azote des espaceurs pyridine et pyrazine participent à nouveau à la coordination du ou des centres métalliques. Ceci a pour conséquence de diminuer la distance entre métaux complexés par rapport aux complexes homologues à espaceur non fonctionnalisé. Les propriétés électroniques des complexes dinucléaires formés avec les ligands biscyclams ont été étudiées par électrochimie et RPE. L étude électrochimique du [Ni2(biscyclam-pyridine)] a montré qu il était à nouveau possible d induire une isomérisation de ces complexes par changement du degré redox du métal. L étude en RPE des complexes dinucléaires [Cu2(biscyclen-pyridine)] et [Cu2(biscyclam-pyridine)] a permis de mettre en évidence une interaction entre les électrons non appariés de chaque cation métallique. Cette interaction est d autant plus forte que la distance métal-métal est courte. Pour les complexes dinucléaires [Cu2(biscyclen-pyrazine)]et [Cu2(biscyclam-pyrazine)], l espaceur se comporte comme un ligand pontant entre les deux centres métalliques et selon le ligand, un chemin d échange magnétique entre les centres métalliques peut exister.In this work, the structural parameters influence on the electronic properties of nickel and copper mono- and bismacrocyclic complexes has been evaluated. In that goal, the ligands under study were monoN-functionalised cyclen and cyclam where the pendant arm was a pyridine group and biscyclen and biscyclam where the inter-cavities spacer was a pyridine or a pyrazine linker. In particular, the influence of exomacrocyclic coordinating atoms on stereochemical and electronic complexes characteristics was studied. For cyclen- and cyclam-pyridine complexes, the X-ray crystallographic analysis has shown that the nitrogen pyridinic atom participates to the metal coordination sphere. For the cyclam-methylpyridine ligand, the complexes synthesis allowed us to isolate two configurational isomers. According to the metal, their electrochemical study has highlighted that the oxidation (for nickel) or the reduction (for copper) process is accompanied by a configurationnal isomerisation between these isomers. For the bismacrocyclic complexes, the X-ray crystallographic analysis has shown when it was possible, that the nitrogen atoms of the spacer (pyridine or pyrazine nitrogen atoms) are also coordinating. By comparison with homologous complexes where the spacer is unfunctionalised, this coordination has resulted in a shorter intermetallic distance. The dinuclear electronic complexes properties were then examined by electrochemistry and EPR spectroscopy. The electrochemical study of [Ni2(biscyclam-pyridine)] has highlighted an isomerisation process between two configurationnal isomeric complexes. The copper complexes [Cu2(biscyclen-pyridine)] and [Cu2(biscyclam-pyridine)] EPR study has above all evidenced an interaction between the unpaired electrons of each metal cation. This interaction is as strong as the intermetallic distance is short. For these dinuclear complexes, the spacer behaves like a bridging ligand between the two metal centers and according to the ligand, a exchange magnetic path way between the metal centers can exist.REIMS-BU Sciences (514542101) / SudocSudocFranceF

Hormonal treatments and mycorrhizal development

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