Halo-alkaliphilic microbes as an effective tool for heavy metal pollution abatement and resource recovery: challenges and future prospects

The current study presents an overview of heavy metals bioremediation from halo-alkaline conditions by using extremophilic microorganisms. Heavy metal remediation from the extreme environment with high pH and elevated salt concentration is a challenge as mesophilic microorganisms are unable to thrive under these polyextremophilic conditions. Thus, for effective bioremediation of extreme systems, specialized microbes (extremophiles) are projected as potential bioremediating agents, that not only thrive under such extreme conditions but are also capable of remediating heavy metals from these environments. The physiological versatility of extremophiles especially halophiles and alkaliphiles and their enzymes (extremozymes) could conveniently be harnessed to remediate and detoxify heavy metals from the high alkaline saline environment. Bibliometric analysis has shown that research in this direction has found pace in recent years and thus this review is a timely attempt to highlight the importance of halo-alkaliphiles for effective contaminant removal in extreme conditions. Also, this review systematically presents insights on adaptive measures utilized by extremophiles to cope with harsh environments and outlines the role of extremophilic microbes in industrial wastewater treatment and recovery of metals from waste with relevant examples. Further, the major challenges and way forward for the effective applicability of halo-alkaliphilic microbes in heavy metals bioremediation from extremophilic conditions are also highlighted.