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Fungal Enzymes in Organic Pollutants Bioremediation
Published in Pankaj Bhatt, Industrial Applications of Microbial Enzymes, 2023
Adam Grzywaczyk, Wojciech Smułek, Jakub Zdarta, Ewa Kaczorek
Reductases, as the name suggests, catalyze reduction reactions. This particular group of enzymes is capable of reducing organic nitro compounds. Representatives of such compounds include nitrotoluenes, furazones, and other aromatic compounds with a nitro substituent. This group of biocatalysts can be divided into two groups—the first and the second type. The mechanism of action of type 1 nitroreductases is the reduction of organic nitro compounds using a two-electron transfer. The operation of type 2, on the other hand, is based on one-electron transfer and the formation of an anionic nitro radical (Song et al., 2015). There is also a further division already in types into groups A and B depending on the reducing agent (NADH or NADPH) and similarities to E. coli nitroreductases NfsA and NfsB. An example of ribbon nitroreductase structure, divided into two monomers, is shown in Figure 6.14.
Ene-Reductases in Pharmaceutical Chemistry
Published in Peter Grunwald, Pharmaceutical Biocatalysis, 2019
The asymmetric bioreduction of activated C=C bonds by ene-reductases has been investigated for decades as the enzyme-catalyzed reaction is a highly specific and environmentally friendly alternative to existing chemical methodologies. Many recent studies have led to the expansion of the toolbox of available ene-reductases (wild-type and engineered libraries) broadening the accessible substrate scope and today, ene-reductase screening panels are offered for sale by a number of commercial suppliers (Table 10.4) shortening industrial development times. However, not only the discovery of novel biocatalysts is of crucial importance but also the capability to develop a commercially viable biocatalytic process. In the case of ene-reductases, the increasing availability of a wide range of cofactor recycling strategies is driving industrial acceptance. Additionally, the productivity of biocatalytic reactions can be further improved by a combination of process engineering (e.g., substrate feeding product removal strategies; enzyme immobilization) and enzyme engineering (solvent tolerance, thermostability, substrate scope, activity). The coming-of-age of ene-reductases as an enzymatic tool for industrial applications will further promote the use of biocatalytic, chemoenzymatic and biosynthetic approaches for fine chemical synthesis.
Bacterial Synthesis of Metallic Nanoparticles
Published in Ramesh Raliya, Nanoscale Engineering in Agricultural Management, 2019
Shweta Agrawal, Mrinal Kuchlan, Jitendra Panwar, Mahaveer Sharma
Bacteria R. capsulate and Stenotrophomonas maltophilia, while bioreducing Au3+ ions to Au0 for the formation of AuNPs, are reported to secrete cofactor NADH- and NADH-dependent enzymes. The reduction seems to be initiated by transfer of electrons from the NADH to NADH-dependent reductase acting as an electron carrier. Finally, the electrons are accepted by the Au (3+) ions and are reduced to Au (0). The amino, sulfhydryl and carboxylic groups of the enzymes, secreted by the bacteria, helps the AuCl4− to bind to the bacterial cell and therefore play crucial role in reducing the Au3+ ions (He et al. 2007, Nangia et al. 2009).
Role of NADH-dependent chromium reductases, exopolysaccharides and antioxidants by Paenibacillus thiaminolyticus PS 5 against damage induced by reactive oxygen species
Published in Chemistry and Ecology, 2020
Parvaze Ahmad Wani, Shazia Wahid, Nusrat Rafi, Uzma Wani
Detoxification of chromium by microbes may occur directly or indirectly and is affected by pH, chromate concentration, incubation periods and the types of microbes involved [21]. Chromium reductases reduce Cr (VI) to Cr (III) [1]. It is also reduced by reductants or oxidants, such as H2S [22]. Conversion of Cr (VI) to Cr (III) by reductases is anaerobic [23], aerobic [24, 25], both anaerobic and aerobic [26]. The reduction of Cr (VI) to Cr (III) is either intracellular, extracellular or membrane bound [1, 27]. Ravindranath et al. [28] used surface-enhanced Raman imagining for the study of intracellular chromate reduction by Shewanella oneidensis. Researchers have purified and characterised reductase in P. ambigua [29] and Bacillus sp. [30]. Heavy metals show adverse effect on various metabolic activities of plants, humans, are the cause of nephrotoxicity [31]. Cr (VI) induced oxidative stress results in over generation of reactive oxygen species (ROS) which damages DNA and alters gene expression [19, 20]. Thus it is important to develop strategies to control pollution of the environment. In this regard, the use of biosorbents and biotransformers is found useful in abating metal pollution [1, 32, 12].
Biotransformation of chromium (VI) by Bacillus sp. isolated from chromate contaminated landfill site
Published in Chemistry and Ecology, 2020
Md. Ekramul Karim, Shamima Akhtar Sharmin, Md. Moniruzzaman, Zeenath Fardous, Keshob Chandra Das, Subrata Banik, Md. Salimullah
Further, AAS analysis of the cell-free extract was carried out and found a total Cr concentration of 9.25 ± 0.187 ppm and 23.24 ± 0.256 ppm for two sets of treatment (10 and 25 ppm), respectively as shown in Figure 3. AAS analysis result indicates that all of the supplemented Cr (VI) was reduced by the strain DHS-12(7) in the extracellular environment and for this reason, most of the supplemented chromium were detected in the cell-free extract. Further investigation was conducted to detect the presence of chromate reductase activity in the extracellular environment, i.e. cell-free extract and found a chromate reductase activity of 15 U/mg of total protein. Previously, Sau et al. [51], reported almost similar chromate reductase activity (8.65 U/mg protein) by cell-free extract of Bacillus firmus KUCr1. The findings of the present study suggest that chromate reductase enzyme is located either in the soluble fractions (cytoplasm) or bound to the membrane of the bacterial cell which is secreted in the extracellular environment and mediates NADH-dependent enzymatic reduction of Cr (VI). These findings are in accordance with many of the previous studies which reported NADH-dependent enzymatic reduction of Cr (VI) [15, 52, 53]. According to Ramirez-Díaz et al. [3], chromate reductase enzyme gains an electron from the oxidation of NADH and transferred it to Cr (VI) to form the intermediate unstable state, Cr (V), which eventually accepts two electrons from other co-substances to produce Cr (III). Soluble reductases are suitable for the development of biocatalysts for bioremediation purposes since those are more amenable to protein engineering to suit the environmental conditions of contaminated sites when compared to the membrane-bound chromate reductases [17].
Review on green nano-biosynthesis of silver nanoparticles and their biological activities: with an emphasis on medicinal plants
Published in Inorganic and Nano-Metal Chemistry, 2021
Fatemeh Moradi, Sajjad Sedaghat, Omid Moradi, Samira Arab Salmanabadi
The ability of microorganisms to secrete large amount of reductase enzymes, makes them an ideal choice for the synthesis of AgNPs in specific sizes and shapes. In addition, there is a large variety of fungi, bacteria, algae and yeast for synthesizing AgNPs in both extra-cellular and intra-cellular methodologies.[26] In extra-cellular synthesis, the enzyme or biomolecules can reduce the trapped metal ions on the outer surface of cells, while the later one occurs inside the cells. According to the literatures, the extra-cellular synthesis of AgNPs is more simple and cost-effective mainly due to the fewer post-synthesis steps required for the regaining of NPs.[27] Recently, Saravanan et al.[25] synthesized AgNPs using Bacillus brevis (NCIM 2533) and studied the antibacterial activity of NPs against pathogenic bacteria. Based on the obtained results, the biosynthesized AgNPs could be utilized as antimicrobial agents against multi-drug resistant pathogens such as Salmonella typhi and Staphylococcus aureus. Also Akther et al.[26] synthesized AgNPs using the endophytic fungus derived from a medicinal plant, Catharanthus roseus (Linn.). Obtained AgNPs were effective in scavenging free radicals and inducing hallmarks of apoptosis in lung (A549) cancer cell lines under in vitro conditions. Marine red algae (Gelidium amansii) was also used for biosynthesis of AgNPs and showed significant reduction of the bacterial growth for both gram positive and gram-negative pathogens.[27] As a comparison, the use of yeast and algae for biosynthesis of AgNPs did not get success as much as fungi and bacteria. Biosynthesis of NPs using fungi have some advantages over other microorganism, especially bacteria,[28] mainly because: (I) Presence of huge enzymes, proteins and reducing components, (II) Fungi are easy to culture to obtain enough required biomass for the synthesis, (III) Extra-cellular secretion of enzymes will reduce the post-synthesis process, and (IV) High wall-binding capacity.