ROLE OF METAL NANOPARTICLES IN MICROBES TO ENHANCE BIOREMEDIATION

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There are numerous microbes that are used to eliminate environmental pollutants as bioremediation agents. Microbes possess the ability to convert complex environment pollutants to simple ions that can be utilized either for the microbe or other living organisms, especially plants, as nutrients to enhance their growth (Rajendran and Gunasekaran 2019). Recently, it was reported that the microbes that belong to species such as Rhodococcus, Alcaligenes, Corynebacterium, Bacillus, Pseudomonas, Arthrobacter, Azotobacter, Mycobacterium, Flavobacterium, Nocardia and Methosinus are used in the bioremediation of soils that are contaminated by the heavy metals, namely zinc, gold, lead, nickel, copper, arsenic, mercury, cadmium and chromium (Girma 2015). Likewise, microbes were also used in the bioremediation of environmental sites that are contaminated by oil spills (Villela et al. 2019), petroleum hydrocarbons (Varjani 2017), radioactive wastes (Roll et al. 2015), polycyclic aromatic compound contaminated soils (Biache et al. 2017) Biache et al. 2017 and wastewater with textile dyes (Kumar et al. 2016). However, the microbes require nutrients for their growth at initial stages to form colonies or biofilms for the conversion of toxic pollutants into nontoxic useful compounds (Kumar et al. 2018). Thus, nanoparticles can serve as nutrients for the initial growth of microbes during the bioremediation process. In addition, biosynthesized nauoparticles with the ability to act as bioremediation will reduce environment pollutants and serve as nutrients or activate certain enzymes in microbes to elevate their pollutant degradation ability.

Apart from nanoparticles activating toxic pollutant degradation ability in microbes, the heavy metals that are degraded and used as nutrients by microbes will be present as intracellular ions, which may help in the formation of intracellular nanoparticles. Thus, degradation of pollutants by microbes can also be useful in the formation of nanoparticles, which can be extracted and used for biomedical as well as other novel applications (Pollmann et al. 2006). Recently, microbial recovery of metallic nanoparticles from industrial waste was proved with mechanisms which is beneficial in environmental cleanup applications. Further, these metal nanoparticles possess ability similar to green synthesized nanoparticles with enhanced biological properties and less toxicity (Pat-Espadas and Cervantes 2018). Magnetosomes are the recent trends in the microbial bioremediation applications that are used to clean up heavily contaminated sites (Vargas et al. 2018). It was reported that certain bacteria possess certain genes with ability to produce magnetic iron oxide nanoparticles called magnetosome crystals, intracellularly, which will be beneficial in heavy metal removal, wastewater treatment and photocatalytic degradation of pollutants (Tajer-Mohammad-Ghazvini et al. 2016). These magnetosome nanoparticles are formed when the growth medium of these bacteria contains a high concentration of iron ions. These magnetic nanoparticles can be extracted from the bacteria as biogenic magnetic nanoparticles that can be employed in bioremediation and biomedical applications (Dieudonne et al. 2019).

Moreover, bacteria with magnetosomes will help as coagulating agents to agglomerate heavy metals present in the contaminated site and remediate them. In addition, these magnetosomes can be removed from the site via magnets which can be reused for further bioremediation (Arakaki et al. 2018). These magnetosomes will be the future of microbial bioremediation applications to transform the contaminated site into a cleaner habitable environment as shown in Fig. 1.

Schematics of magnetosomes and their application in bioremediation of contaminated soil

Figure 1 Schematics of magnetosomes and their application in bioremediation of contaminated soil.

FUTURE PERSPECTIVE

Currently, nanoparticles are used as standalone bioremediation agents with photocatalytic degradation of pollutants, antimicrobial, wastewater treatment ability and as nutrients and enzyme triggering agents among microbes to act as bioremediation agents. In future nanoformulation consisting of a combination of different types of nanopaiticles will replace the standalone nanoparticles in environment. These nanoformulations will be prepared by polymers extracted from microbes or plants or dendrimers with biomolecules. Further, the nanoformulation will contain compartments to hold various nanoparticles with distinct properties such as antimicrobial, photocatalytic degradation, biofertilizer and enzyme-triggering abilities. The application of these biogenic nanoformulation will degrade in the contaminated environment to release the specific nanopaiticles. The nanoparticle with antimicrobial property will help in inhibiting toxic microbes

Schematic representation of nanoformulations in the environmental bioremediation from the environment

Figure 2 Schematic representation of nanoformulations in the environmental bioremediation from the environment. Likewise, nanoparticle with photocatalytic degradation ability will reduce toxic organic dyes from the environment using solar irradiation. Further, nanoparticles with wastewater treatment ability will help to coagulate pollutants present in surface or ground water bodies and reduce their effective toxicity by removing them. Furthermore, nanoparticles can also serve as biofertilizers by dissolving in the contaminated site, serving as nutrients for the growth of plants to reduce pollutants via phytoremediation process and helping microbes in bioremediation by triggering specific enzymes. Thus, a single nanoformulated particle will clean the contaminated site and transform them into a habitable environment, as shown in Fig. 2, instead of several nanoparticles. In future, these nanoformulated agents will replace the conventional bioremediation nanoparticles to elevate their efficiency in bioremediation applications. Moreover, synthesizing each encapsulated nanoparticle via biological approach and coating gold nanoparticles to detect contamination to release specific concentration of nanoparticles will enhance the effectiveness of the nanoformulated bioremediation agents in future for environmental applications.

CONCLUSION

The present chapter is an overview of different metal nanoparticles that are used in bioremediation and the role of metal nanoparticles synthesized via biological agents such as microbes and plants, as an efficient, non-toxic bioremediation agent. In addition, the significance of biosynthesized metal nanoparticles and its ability in altering microbes and the use of magnetosomes for efficient bioremediation were also discussed. These metal nanoparticles will reduce the limitations of conventional microbial and phytoremediation methods and replace them to effectively reduce pollutants in environments. Further, the future of bioremediation will be the nanoformulated bioremediation agents with potential to encapsulate several nanoparticles with environmental bioremediation property to clean up the contaminated sites.

 
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