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Arsenic Toxicity in Water-Soil-Plant System An Alarming Scenario and Possibility of Bioremediation
Published in Amitava Rakshit, Manoj Parihar, Binoy Sarkar, Harikesh B. Singh, Leonardo Fernandes Fraceto, Bioremediation Science From Theory to Practice, 2021
Ganesh Chandra Banik, Shovik Deb, Surajit Khalko, Ashok Chaudhury, Parimat Panda, Anarul Hogue
A number of rhizo spheric bacteria (like Rhizobium, Frankia, Klebsiella, Closfridium, Bacillus, Pseudomonas, Azotobactor) are partially resistant to arsenic and also have plant growth promoting abilities and thus have considerable role in bioremediation of arsenic (Gupta et al. 2015). On the contrary, some of the bacterial genera like Aeromonas and Exiguobacterium can directly interact with the soil arsenic. Many other bacteria are able to oxidise arsenite into the less toxic arsenate. The oxidation of arsenite is catalysed by arsenite oxidase enzyme (Krugar et al. 2013). A common site for arsenite oxidation is the periplasm of the bacteria (Silver and Phung 2005). Few genera of bacteria are also able to reduce arsenate to arsenite using arsenate reductase enzyme. The reduced arsenite is either released from the cell or accumulates into the intracellular compartments, in the form of free arsenite or gets combined with glutathione or other thiols. In general, gram-positive bacteria has been found as more efficient in using higher concentrations of arsenic compared to gram-negative bacteria. Few bacterial genera like Alcligenes, Pseudomonas and Mycobacterium have been found to have role in arsenic methylation (Hughes 2002).
Synechocystis sp. PCC 6803
Published in Yong-Guan Zhu, Huaming Guo, Prosun Bhattacharya, Jochen Bundschuh, Arslan Ahmad, Ravi Naidu, Environmental Arsenic in a Changing World, 2019
Y. Yan, J. Ye, X. Zhang, X.M. Xue, Y.G. Zhu
Arsenate reductase from Synechocystis sp. PCC 6803 (SynArsC) is a novel ArsC belonging to the Trx/Grx hybrid arsenate reductase family. The primary sequence of SynArsC is similar with that of Trx-dependent ArsCs, whereas SynArsC utilized Grx/GSH system for arsenate reduction (López-Maury et al., 2009; Li et al., 2003). Cys8, Cys80 and Cys82 in SynArsC were identified as essential cysteine residues by site-directed mutagenesis, and the Cys80/Cys82 disulfide was detected by equilibrium redox titrations. In order to elucidate the special mechanism of As(V) reduction, we determined the crystal structures of native SynArsC and its complex with phosphate (PO43−).
Progresses and emerging trends of arsenic research in the past 120 years
Published in Critical Reviews in Environmental Science and Technology, 2021
Chengjun Li, Jiahui Wang, Bing Yan, Ai-Jun Miao, Huan Zhong, Wei Zhang, Lena Qiying Ma
Due to concerns and mounting evidence of dietary arsenic exposure, arsenic bioaccumulation and biotransformation in plants, especially in crops (Zhao, Ma, Zhu, Tang & McGrath, 2015), have been a hot topic in which many research trends have emerged during the past few years. There are two forms of iAs, AsV and AsIII that can be easily taken up by plant roots, while AsV is a chemical analog of phosphate that can disrupt at least some phosphate-dependent aspects of metabolism (Finnegan & Chen, 2012). Once in cells, AsV can be readily converted to AsIII, the more toxic arsenic species; however, the enzyme(s) catalyzing this reaction in rice remained unknown until recent years. In 2014, a new AsV reductase, i.e., high arsenic content 1 (HAC1) (Shi et al., 2016) or arsenate tolerance QTL 1 (ATQ1), was identified in Arabidopsis thaliana. Two years later, two similar arsenate reductases in rice, OsHAC1;1 and OsHAC1;2 were identified by Shi et al. (2016). After uptake and reduction, arsenic is transported via different pathways. Song et al. (2010) first identified two ABCC-type phytochelatins in A. thaliana, i.e., AtABCC1 and AtABCC2, as the major transporters in plant vacuoles. Mutants without these two transporters are sensitive to arsenic whose arsenic uptake is dramatically reduced. Similarly, a rice mutant defective in OsPHF1 (for phosphate transporter traffic facilitator1) was reported to lose much of the ability to take up phosphate and arsenate and to transport them from roots to shoots. In contrast, transgenic rice plants overexpressing such transporters have enhanced phosphate and arsenate uptake and translocation abilities (Wu et al., 2011). Moreover, a rice ABC transporter, OsABCC1, has been identified in the upper nodes of rice plants that can restrict the distribution of arsenic to the grain by sequestering it in the vacuoles of the phloem companion cells of diffuse vascular bundles directly connected to the grain (Song et al., 2014). (Figure 11). Generally, 10–90% arsenic in rice grains presents as DMAV and the remainder presents as iAs (Meharg et al., 2009); however, rice cannot methylate iAs (Lomax et al., 2012). Instead, it takes up methylated arsenic produced by microorganisms via arsenic methyltransferase (arsM) (Lomax et al., 2012). Soil flooding and additions of organic matter can facilitate microbial methylation of arsenic, corresponding to the elevated abundance of the arsM genes in the soil (Jia et al., 2013; Zhao et al., 2013). In fact, the microbial communities involved in arsenic bioaccumulation and biotransformation are widely distributed, with highly diverse and abundant arsenite oxidase (aioA), respiratory arsenate reductase (arrA), arsenate reductase (arsC), and arsM genes (Zhang, et al., 2015). It has also been shown that arsenic uptake by rice can be influenced by many microbial processes, especially arsenic oxidation in the rhizosphere, and these processes are influenced by root radial oxygen loss and organic matter application (Jia et al., 2014; Zhu, Xue, Kappler, Rosen & Meharg, 2017).