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

Chromium Resistant Bacteria: Impact on Plant Growth in Soil Microcosm

Three chromium resistant bacterial strains, Pseudomonas fluorescens PF28, Enterobacter amnigenus EA31 and Enterococcus gallinarum S34 isolated from tannery waste contaminated soil were used in this study. All strains could resist a high concentration of K2Cr2O7 that is up to 300 mg/L. The effect of these strains on clover plants (Trifolium campestre) in the presence of two chromium salts CrCl3 and K2Cr2O7 was studied in soil microcosm. Application of chromium salts adversely affected seed germination, root and shoot length. Bacterial inoculation improved the growth parameters under chromate stress when compared with non inoculated respective controls. There was observed more than 50% reduction of Cr(VI) in inoculated soil microcosms, as compared to the uninoculated soil under the same conditions. The results obtained in this study are significant for the bioremediation of chromate pollution

Theoretical and experimental adhesion of yeast strains with high chromium removal potential

International audienceBiofilm-based bioprocesses are increasingly used in wastewater treatment. Microbial adhesion constitutes the key step in stability of these depollution systems. For adhesion studies, physicochemical characterization of microbial cells and supports has proved to be of extreme importance. In this work, estimation of interaction between five yeast strains with a high potential for Cr (VI) removal using extended Derjaguin–Landau–Verwey and Overbeek (XDLVO) theory as a powerful predictive tool of adhesion was investigated. Predictions showed that wood husk could be a good support for the formation of tested yeast biofilm, beech and oak exhibit better properties than other wood species studied with 100% of potential for adhesion. From a thermodynamic point of view, pine and teak woods are not suitable for biofilm formation for all tested yeast strains, presenting positive values of free energy adhesion (ΔGXDLVO). Environmental scanning electronic microscopy (ESEM) and Matlab® image analysis confirmed that all tested yeast strains were able to adhere to pine wood and, except for Wickerhamomyces anomalus they were unable to adhere to oak wood. Adhesion experiments were found to be well related to the theoretical prediction. To our knowledge, this is the first study dealing with biofilm-mediated depollution from an adhesion point of view aiming to optimize the stability of the system. It allows expanding knowledge about adhesion phenomena of yeast strains on wooden surface and contributes to select the best biofilm-support combination that would be used in a performant biological system for chromium removal

Étude du pouvoir réducteur du chrome hexavalent de trois isolats de levures : élaboration d’une stratégie de bioremédiation

Les effluents et les boues des tanneries sont considérés parmi les rejets industriels les plus polluants, charriant de fortes concentrations de chrome hexavalent toxique. Les procédures biologiques de décontamination des eaux polluées par le chrome semblent présenter des avantages significatifs par rapport aux méthodes physico-chimiques. Dans ce cadre, trois isolats de levures sont isolés à partir des effluents des tanneries de la ville de Fès (Maroc) et sont étudiés pour leurs capacités à réduire le Cr(VI) et leur résistance au chrome et à d’autres métaux (Co(II), Cu(II), Ni(II), Zn(II), Hg(II), Pb(II)). Les résultats montrent que les isolats résistent à des concentrations importantes de Cr(VI) et d’autres métaux lourds et sont capables de réduire complètement 0,5 mM de Cr(VI) en 48 h, en milieu liquide en conditions aérobies. La capacité de réduction du Cr(VI) par les isolats au niveau du sol permet de limiter la toxicité de ce métal vis-à-vis des plantules de trèfle à travers sa réduction au niveau du sol. Les isolats de levures pourraient être utilisés pour la bioremédiation du sol et des effluents contaminés par le Cr(VI)