Tarek Moussa

Extremophiles are a group of organisms growing in a wide range of extreme environmental conditions. The extremophilic microorganisms are diverse and are classified into psychrophiles (− 2°C to 20°C), thermophiles (55–121°C), piezophiles (> 500atm), halophiles (2–5M NaCl or KCl), metallophiles (high concentrations of metals, e.g., copper, zinc, lead, cadmium, and arsenic), alkaliphiles (pH>8), and acidophiles (pH<4) according to the extreme environmental conditions in which they grow and can tolerate. The aims of this chapter are to characterize the extremophilic microorganisms and their physiological and molecular efficiencies in bioremediation processes. Interestingly, the remarkable adaptative abilities of extremophilic microorganisms make them an attractive source of biocatalysts for bioremediation. Bioremediation is an important technology for the cleanup of environmental contaminants. Further attention has also been directed to isolation, identification, and characterization of biocatalysts from extremophilic microorganisms, most of them enzymes named extremozymes, which are well adapted to be active also at extreme conditions. Extremozymes are expected to fill the gap between biological and chemical industrial processes because of the remarkable properties of these enzymes. Even though more than 3000 different enzymes have been identified till now, and many of these were used in industrial and biotechnological applications, the enzyme toolbox at the present is still not enough to present demands. A major cause for this is the fact that many available enzymes do not withstand industrial reaction conditions.

Dielectric constant (ε, epsilon) is one of the basic physical parameters for materials, determining the response of materials to electromagnetic waves or electrical field; its value is generally positive. In fact, dielectric constant can also be negative, regarded as supernormal performance to some degree. The negative dielectric property has become research hotspot as an essential key for constructing metamaterials, showing unique and exotic electromagnetic properties not existing in naturally occurring materials, such as negative refraction, perfect troubles, and reverse Doppler effect. Recently, the feasibility is demonstrated to achieve negative dielectric property in conventional heterogeneous composites rather than periodic artificial arrays; drawing great attention from researchers in material science and engineering, many advances have been made and can promote the development of metamaterials and conventional electromagnetic functional materials. Here, we reviewed the recent advances in negative dielectric property designed in some heterogeneous composites, including metal composites, carbon composites, ceramic composites, conducting polymer. Besides, various strategies, including designing different microstructures, changing the working temperatures, choosing flexible matrix or fillers, electro-magnetic coupling, were summarized to precisely adjust negative dielectric property. Finally, the question unsolved and perspectives about negative dielectric property are put forward; we expect to shed light on the mechanism of negative dielectric property as well as its relationship with the material design in composition and microstructure.