A review on the Genetically Engineered Microbes for Bioremediation of THMs namely Hg and Cr.

Bioremediation is well established as the economical, sustainable, and viable solution to the toxic heavy metal pollution generated from heavy industrialization. Metal pollutants affect our ecosystem and endanger the lives of millions of people all around the world, both in developed and developing countries[1][2]. Water bodies and land are equally affected and the health issues that stem from THM pollution, increase the burden on the healthcare and economy, which is more prominent in developing countries. Also, these changes in the ecosystem are long-lasting from which it's difficult to recover naturally. It requires special interventions to bring back the balance. Recently the growing concerns towards heavy metal pollution and inclination towards sustainable development has spurred the growth of bioremediation strategies. The field of bioremediation has evolved over the past few decades, owing to the tremendous addition to the knowledge and growth of genetics and genomics. At present, various tools of genetic engineering are employed to tackle this challenge using various microorganisms, plants, and both. Researchers are moving from a single microorganism system to consortium-based approaches as well. With the advent of synthetic biology tools, their integration into the conventional bioremediation strategies is also taking place. Many of these tools and modifications are quite promising and have seen field applications recently as well. However, several hurdles are there that pose a challenge to the efficient utilization of genetically engineered microbes in treating the sites of contamination, particularly the efficiency of the microorganism in open field application, the effect on native flora, and dynamic or hostile field factors[3]. Among various successful examples of the application of genetically engineered microbes, some can be considered milestones which include the use of “mer” resistance genes for the treatment of Hg and “ChrR” in the treatment of chromium[4]. Strain stabilisation and optimization strategies have greatly improved and a huge resource of information is now accessible for young researchers, like the list of plasmids compatible with bacterial strains and each other. All these developments open up new avenues of research and indicates a sustainable future. The mode of application of bioremediation strategies varies depending on the type, site and size of the polluted area. The scale of application of these strategies also vary accordingly. Social awareness and willingness of people to adopt these strategies also come into play. The gap of awareness within the public and their hesitation to employ bioremediation strategies need to be addressed. This review attempts to summarize most of the aspects and impact of heavy metal pollution. It emphasizes the importance of genetically engineered microbes for bioremediation purposes. It also highlights the need for active research to tackle the challenges to the open field applications of genetically engineered microbes for the bioremediation of toxic heavy metals. It also discusses the need for efforts to make the public aware of the health impact of heavy metal pollution[5]. Public awareness, along with the scientific inputs is the only way with which sustainability can be achieved and the heavy metal pollution can be controlled and remediated.