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The engineering of enzymes with altered activity, specificity, and stability, using directed evolution techniques that mimic evolution on a laboratory timescale, is now well established. In vitro recombination techniques such as DNA shuffling, staggered extension process (StEP), random chimeragenesis on transient templates (RACHITT), iterative truncation for the creation of hybrid enzymes (ITCHY), recombined extension on truncated templates (RETT), and so on have been developed to mimic and accelerate nature's recombination strategy. This review discusses gradual advances in the techniques and strategies used for the directed evolution of biocatalytic enzymes aimed at improving the quality and potential of enzyme libraries, their advantages, and disadvantages.

The presence of chromium in industrial effluents has become a huge problem worldwide as hexavalent chromium is highly toxic to animals due to its ability to generate reactive oxygen species in cells. The trivalent state of chromium, on the other hand, is significantly less toxic and also serves as an essential element in trace amounts. When industries such as electroplating, tannery, dyeing and others release their effluents into water bodies, hexavalent chromium enters the food chain and, consequently, reaches humans in a biomagnified form. Many remediation processes for removal of hexavalent chromium have been researched and reviewed extensively. These include chemical reduction to trivalent chromium, solvent extraction, chelation and adsorption, among others. It has been generally concluded that adsorption (and/or subsequent reduction) of hexavalent chromium is the best method. However, relatively little is known about the potential of using nanoparticles as adsorbents for the removal of hexavalent chromium from industrial effluents. This method of nanoremediation is more effective than conventional remediation methods and is cost-effective for the industry in the long run. This article reviews the various remediation methods of hexavalent chromium, with emphasis on the field of nanoremediation.

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