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Omics Reflection on the Bacterial Escape from the Toxic Trap of Metal(loid)s
Published in Vineet Kumar, Vinod Kumar Garg, Sunil Kumar, Jayanta Kumar Biswas, Omics for Environmental Engineering and Microbiology Systems, 2023
Jayanta Kumar Biswas, Monojit Mondal, Vineet Kumar, Meththika Vithanage, Rangabhashiyam Selvasembian, Balram Ambade, Manish Kumar
Resistance to Zn(II), Cd(II), and Pb(II) in bacteria is mostly reliant on active metal ion efflux to prevent harmful effects on the cell, which are mediated by chromosomes, plasmids, or transposons (Bruins et al. 2000). An ATPase efflux pump is encoded by the cop operon (genes of copA, copB, copZ, and copY) (Bruins et al. 2000) (Table 16.1). The copA gene encodes for a Cu(II) uptake ATPase, while copB gene encodes for a P-type efflux ATPase (Etesami 2018). Plasmid-encoded As (V) resistance and antimonite resistance mediated by the ars operon are two more notable instances of this resistance system (Etesami 2018). The ars operon (genes of arsA, arsB, arsC, arsD, and arsR) codes for an ATPase efflux pump as well as the arsenate reductase-detoxifying enzyme (Bruins et al. 2000; Etesami 2018).
Exploration and Intervention of Geologically Ancient Microbial Adaptation in the Contemporary Environmental Arsenic Bioremediation
Published in Edgardo R. Donati, Heavy Metals in the Environment, 2018
Tanmoy Paul, Samir Kumar Mukherjee
Decontamination of arsenic from environment is of great significance to local agriculture and the population elsewhere in the As-affected area. The conventional techniques for the decontamination of As includes chemical precipitation, chemical redox reactions, ion exchange, filtration, and reverse osmosis (Malik, 2004). The disadvantage of these techniques includes less accuracy, particularly, in very low As concentration (Chaalal et al., 2005) and secondary environmental pollution due to the chemicals used in the remediation process. The cost that is involved restricts the utilization of the prevailing techniques. In recent years, bioremediation of heavy metals using microorganisms has gained attention. Microorganisms play major roles in the biochemical cycle of arsenic and can convert to different oxidation states with different solubility and mobility, therefore influencing the toxicity (Silver and Phung, 2005). Certain microorganisms in nature have evolved the needed genetic components that provide resistance mechanisms which enable them to survive and grow in an environment containing toxic levels of arsenic. The ars operon located on genomes of prokaryotes which confers As resistance is well characterized (Xu et al., 1998). The microbial As detoxification involves the reduction of As(V) to As (III) via cytoplasmic arsenate reductase (arsC) and further, As (III) is extruded by a membrane associated with arsB efflux pump. Other genes such as arsR, arsD, and arsA form part of ars operon along with arsB and arsC in most prokaryotes (Rosen, 2002). Considering the threat of As to human health, the future challenge is to remove this toxic metalloid from our habitable ecological niche. The myriad arrays of As resistant adaptations in contemporary life forms are the evolutionary tools for the sustainable environmental As decontamination. Furthermore, deeper investigations for linking As resistant properties of organisms with respect to their life history and the environmental issues leading toward As decontamination are essential for successful bioremediation.
Molecular Approaches for Removal of Toxic Metal by Genetically Modified Microbes
Published in Maulin P. Shah, Wastewater Treatment, 2022
Joorie Bhattacharya, Rahul Nitnavare, Sougata Ghosh
Arsenic is one of the most toxic metalloids and contributes to a majority of the world's heavy metal water pollution. Arsenic exists in two states in the environment, viz., arsenite [As(III)] and arsenate [As(V)] out of which its pentavalent form is known to be less toxic. In addition to this, arsenic is associated with a variety of human diseases such as skin, lung, and kidney cancer. Arsenic toxicity is commonly due to the binding of arsenite to thiol groups and the substitution of arsenate with phosphate groups in the cell. There have been several studies demonstrating the efficacy of microorganisms in arsenic bioremoval by the induction of proteins that bind to the heavy metal. This has been attributed to specific mechanisms of metalloregulatory proteins that confer resistance. In Escherichia coli, the ars operon governs resistance in the microorganism. The proteins associated with the operon sense arsenite in the environment and activate certain trans-acting repressors. The ArsR protein specifically has a high affinity toward As(III). Overexpression of the arsR gene demonstrated enhanced binding and bioaccumulation of arsenic in E.coli cells as seen in Table 5.1 The accumulation ability of the bacteria was observed at 12 and 24 hours after incubation with sodium arsenite. It was observed that at low expression of arsR at 12 hours, the bioaccumulation was also minor. However, at 24 hours when the expression level of arsR had significantly increased, the bioaccumulation had also improved by fourfold. At 48 hours, where no expression of ArsR was observed, the bioaccumulation was found to increase by 13-fold. The efficacy of resting cells has also been studied for the bioaccumulation capacity of arsenic. The binding level observed was at par with growing cells at around 50 µM arsenite, and the values obtained were virtually the same. This suggested that resting cells were as effective and stable as growing cells and can be explored for arsenic binding in contaminated soil and water. In order to examine the removal of arsenic from contaminated water by recombinant bacteria, resting cells were incubated with the water contaminated with arsenic to 50 parts per billion (ppb). Increasing the cell load from 0.9 to 9 mg/mL enhanced the bioaccumulation from 54% to 98%, suggesting its high selectivity toward the metalloid (Kostal et al., 2004). However, because of the infectious nature of the bacteria, researchers have often looked for alternative microorganisms.
Groundwater inhabited Bacillus and Paenibacillus strains alleviate arsenic-induced phytotoxicity of rice plant
Published in International Journal of Phytoremediation, 2020
Adrita Banerjee, Anjan Hazra, Sauren Das, Chandan Sengupta
It is well established that arsenic redox cycling by microorganisms plays a significant role in controlling arsenic speciation and mobility in high arsenic environments (Ghosh et al. 2018). Microorganism which inhabits within groundwater has been shown to affect the arsenic geochemistry by catalyzing redox transformations and other reactions that affect the mobility of this metalloid in subsurface environment (Lloyd and Oremland 2006; Bachate et al. 2012; Liu et al. 2012). Certain microorganisms in nature have evolved the needed genetic components that provide resistance mechanisms enabling them to survive and grow in an environment with elevated arsenic toxic levels (Achour et al. 2007). The plasmids/chromosomal linked “ars” operon in prokaryotes is well characterized and play a key role in arsenic resistance mechanism (Xu et al. 1998; Fekih et al. 2018).
Characterization of arsenite-oxidizing bacteria to decipher their role in arsenic bioremediation
Published in Preparative Biochemistry and Biotechnology, 2019
Phylogenetic analysis of the partial sequence of 16 s rRNA gene of the selected strain showed its sequence homology with several Bacillus spp. Belonging to Firmicutes family, with a high bootstrap value of more than 95% (Figure 3). Previous report revealed that most of the As3+-oxidizing strains isolated from the upper and middle Indo-Gangetic plains are of the genera Pseudomonas and Bacillus[28] (Table 2). The strains from Bacillus genus are well-known for their quick adaption in adverse environment due to their spore forming ability. Arsenic transformation ability of Bacillus sp. was also reported by Lio et al. (2011) with an efficiency of 65% of As transformation.[29] Gene-mediated As resistance potentiability of Bacillus groups have been reported over time. Moreover, the presence of an ars operon can be speculated in this bacteria, containing carrier proteins and genes arsRBC through which they can exude the As5+ out of the cell.[30] The highly efficient strains isolated from the central Gangetic plains of Bihar, have a more superior transformation ability and can have a severe positive impact on the bioremediation of As and other heavy metals of the region.
Statistical optimization of arsenic biosorption by microbial enzyme via Ca-alginate beads
Published in Journal of Environmental Science and Health, Part A, 2018
Suchetana Banerjee, Anindita Banerjee, Priyabrata Sarkar
Many procedures such as oxidation/precipitation, sorption onto activated carbon, co-precipitation/ coagulation, lime softening, reverse osmosis, ion-exchange, membrane techniques have been used for arsenic removal although the above methods have certain drawbacks e.g., high operational cost, lower efficiency, production of harmful chemical sludge and limited tolerance to pH change.[5–8] Mechanisms and degree of arsenic adsorption depend greatly on the speciation of the inorganic arsenic forms which in turn depends on the pH and the redox potential (Eh) of the solution.[9] Organisms have developed several tolerance mechanisms to survive in the toxic arsenic-containing environments such as detoxifying reduction of As (V) to As(III) by the cytoplasmic ars operon that is often located on plasmids or transposons that synthesizes the arsenate reductase enzyme.[10–12] Substantial research on microbiological processes that regulate the mobilization and distribution of As in aquatic environments has been carried out. Pseudomonas species along with other organisms are known to have high metal binding capability as well as very high As (V) tolerance and can be used as metal-adsorbing agents.[13,14]