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ISSN: 2155-6199
Journal of Bioremediation & Biodegradation
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Arsenic as Next Global Threat? Role of Biotechnological Approaches

Bhatt SM*
Biotechnology Department, Lovely Professional University, Punjab, India
*Corresponding Author : Bhatt SM
Biotechnology Department
Lovely Professional University
Punjab, India
E-mail: [email protected]
Received January 11, 2016; Accepted February 01, 2016; Published February 10, 2016
Citation:Bhatt SM (2016) Arsenic as Next Global Threat? Role of Biotechnological Approaches. J Bioremed Biodeg 7:329. doi: 10.4172/2155-6199.1000329
Copyright: © 2016 Bhatt SM, et al. This is an open-a ccess article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.

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Abstract

Arsenicosis is about potent toxicity and carcinogenic effect of arsenic but sometime it had been used for medicinal purpose in old times also. Nowadays it has been emerging as a new threat for human community at large because of recent report of arsenic mobilization in food chain. Study reveals presence of high arsenic concentration not only in drinking water but also in in many food crops, meat and other consumables. Many part of world is facing acute crisis such as Bangladesh, china India, and many more countries as depicted in Figure 1 and in more than 70 countries, peoples are severely effected by groundwater arsenic contamination and need urgent interventions. Bangladesh has been declared as one of the worst natural calamities where rural and urban communities are facing severe consequences in form of skin cancer such as keratosis and melanosis. In India, Malwa, Punjab, has been declared as Cancer belt, where intense sign of cancer has been reported in skin and other vital organs.

Keywords
Carcinogenic effect; Arsenate; P. vittata; Aquaglycoporins
Introduction
Metalloid arsenic has several structural form (Table 1), and cancombine with many metals such as iron and molybdenum but ArsenicIII (inorganic form) is most toxic form and is accumulating and enteringin food chain constantly, escalating arsenic mobility issue more thancalculated one. Further environmental condition such as pH, floods(redox condition), are conducive in high mobility and interconversionsof arsenic getting complexed with many other compounds, favouringtheir easy transport in rice and other seeds via multiple transporterse.g., aquaglyceroporins in both plant and animals [1].
Marine organism had exceeding high levels of arsenic accumulationin non-toxic organic form arsenobetain, while rice is reported to haveexceeding levels of inorganic arsenic (III). Arsenate As (V) is nontoxicform but it becomes toxic when arsenic (V) combines withphosphate or iron oxide and thus inhibits phosphorylation processesafter entering the cells. Arsenate As (III) causes deactivation of enzymedue to its high affinity towards thiol groups. In addition, inorganicarsenic enters the cell via the hexose transporter, phosphate transportersystems (PTS) or aqua-glycoporins, while rice and other plants haddifferent transporter. Arsenic reductase coded by Ars or Arr operonare helpful in conversion of arsenite to arsenate in both prokaryotesand eukaryotes and some microbes has ability to pump out exceedingarsenite after detoxification. Arsenic detoxification in multicellularorganisms is based on methylation pattern and further oxidation makesarsenic less toxic basically arsenic (III) is converted into arsenic (V) which is excreted in urine of human being. However, since human haslimited capacity of conversion, therefore high accumulation causesvarious malfunctioning such as keratosis and melanosis.
Microbial action is thought to provoke high mobilisation ofarsenic via arsenic reductases after solubilisation of arsenic complexdue to chelation. Methylation is believed to be one of the importantmechanisms present in all organism including many microbes such asbacteria, fungi, and even higher plants, other organisms that convertsthem back in non-toxic form. Mostly, alternative oxidation andreduction is the basis of conversion of one form of arsenic into other.Even though arsenite is more toxic than arsenate, this transformation isessential, since only arsenite can be methylated. Arsenite is methylatedto methylarsonate, which is reduced to methylarsonite and further todimethylarsinate and to dimethylarsinous acid [2].
Arsenic contamination in non-effected area is of great concerntoday and spreading via food chain. Old strategies for arsenic mitigationwere not only costly, but also results in large amount of sludgeproduction, which was difficult to detoxify in one-step. Many workerbelieves that comprehensive multistep approaches towards escalatingproblems is essential in mitigation of arsenic means both chemical aswell as biotechnological approaches can work in synchronous matter.Therefore, alternative techniques may be helpful in order to prevent theentry of arsenic in the food chain. One of the most relevant strategiesseems to be the application of arsenic resistance microbes equippedwith both uptake and detoxification machinery for sequestration andintroduction of novel genes into food crops. Many endophytes isolatedfrom hyper accumulator’s plants have role in mobilization of arsenic.Metagenomics approaches seems to be plausible in finding potentialmicrobes in order to enhanced bioremediation capability of arsenic onthe basis of presence of clusters of genes and gene networks present for As sequestration and metabolism [3]. Many hyper accumulators areknown to adsorb more than 95% of the arsenic from the soil as evidentby the fern (P. vittata) [4]. Unfortunately, the plant P. vittata growswell only in warm, humid environments with mild winters, thereforethey cannot grow everywhere in every environment. Therefore, somescientist are making efforts to increase the ability of plants to pumpout arsenic from soil via creating GMO plants which have gene forboth mobility and sequestration of arsenic and beside this somemore gene required like metal chelator, metallothionein (MT), metaltransporter, and phytochelatin (PC) genes [5]. Dhanker and colleaguesconstructed Arabidopsis plants, where, γ -ECS gene related to mobilitywas introduced and the arsenate reductase C (ArsC) gene to control thesequestration of arsenic [3,6,7]. Compared to other techniques, biomassbased techniques are more useful. Some research on endophytes relatedto bioremediation and use of arbuscular mycorrhizas (AMs) are alsoinvolve absorption of arsenic. Mycorrhizas are vital for some plantssince these are fungi associate with plant roots, so an important tools inincreasing uptake of nutrients, especially phosphorus. AM fungi may behelpful in increased arsenic uptake along with hyper accumulating fernP. vittata The arsenic translocation factor (TF) was reported to increasein AM-inoculated plants as compared with Uninoculated plants, forexample in Glomus mosseae-inoculated plants TF factor was 730 ascompared to 50 as compared to control plants. Since arsenate sharesstructural similarity with phosphate and thus many hyper accumulatorspecies such as P. vittata absorbs arsenate via phosphate transportsystem (PTS) or with other metal transporter system [8]. Secretion ofvarious chemical chelators also increases rapid uptake of arsenic butmostly plants lacks adequate system to adsorb arsenic rapidly.
Some edible microbes such as Lactic acid bacteria has various specialcharacteristic features such as secretion of antibacterial substances(bacteriocins) presence of arsenic reductase (Ars C). Lactobacillus lactisreported to contains GSH which protects bacterium under extremeacidic conditions [9,10]. Use of LAB is limited in adsorption since they requires surface modifications for perfect adsorption of arsenic. Thereare presence of many secondary transporter Ars A, Ars B, Ars C operonthat makes them arsenic resistant bacteria but they fail to adsorbCobalt, Copper, Nickel, and Iron metals [9]. Bacillus adsorb wide rangeof metals such as mercury, lead and cadmium, while Staphylococcus, E.coli, Lactobacillus are arsenic resistance [11,12]. Known Lactobacillusspecies for arsenic are Lactobacillus acidophilus, L. Crispatus, whilePseudomonas proteda, Bacillus subtilis, L. rhamnosus, Bifido bacteriumand Lactobacillus plantarum [9,13,14]. Both facultative aerobic andanaerobic e.g., bacillus, clostridium reported to remove metal ionsrapidly [15-17]. Presence of metal resistance shows microbial capabilityto survive in the environment, which can be harnessed as an effectivemitigation strategy for arsenic [11,18,19]. Arsenite III is mostlydominating in anoxic water such as floods and via root uptake enters inseedlings. DARP (Dissimilatory Arsenate-respiring prokaryotes) [20]is associated with arsenic reduction via electrons exchange via releaseof chelators such as lactate, acetate and formate. These microbes utilizes‘arr’ biomarkers [21] and thrive well in deep sea, deep well and lake orcontaminated aquifers [22].
For arsenic detoxification arsenate and arsenite operon is presentin both the gram positive as well as gram negative bacteria. arr operonis related to arsenic reductase present in many microbes such asShewanella, bacillus some organism like E. coli, Staphylococcus, Bacillus,Acidithiobacillus, Pseudomonas, had well characterised Ars operonlinked with As(V) detoxification where. In these organisms, As (V) isconverted to As (III) via arsenic reductase, which triggers ars operon.Actually, these operons are linked with efflux and transporter protein,as a result arsenic V enters via phosphate transporter protein while ArsIII is efflux after activation of Ars operon [16]. Endophytes are part ofplant system and thus may help in mobilisation of nutrients and arsenicalong with Arsenic V which is analogous to phosphate while somerhizospheric endophytes stops mobilization of arsenic metals. Thereis more bioavailability of arsenic or deposits of arsenic. Rather than single microbes to act for decontamination groups of microbes (calledas Biome) activates for maintaining balance between toxic metals.Recently, addition of SiO, or iron oxide (Fe2O3 or Fe3O4) nanoparticle insoil resulted in increasing growth of specific micro-organism speciallyanaerobic arsenic reducing microbes, which resulted in enhanceduptake, via rapid mobilization and precipitation of arsenic in presenceof sodium acetate. This reduction strategies is actually depends onpresence of specific operon, such as Arr operon. Treatment of NPswith sodium acetate increases precipitation of arsenic due to electrondonating capacity [23,24]. In assisting microbial bioremediation plantsmay have vital absorptive role in aim to survival strategies, Bayer et al.[25,26] has recently studied a detail mechanism of interaction betweenplant and microbes via metagenomics study [48]. In conclusion, moreresearch effort is required in pilot scale study which may represent aconfirmative mitigation of arsenic from food chain [49,50].
References

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Review summary

  1. Aerin
    Posted on Sep 21 2016 at 12:56 pm
    The paper try to review the environmental problem of As, and the environmental effect and the potential removal processes were presented. the topic is interstering. More research effort is required in pilot scale study which may represent a confirmative mitigation of arsenic from food chain.
 

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