Insights into microbe assisted remediation in plants: a brief account on mechanisms and multi-omic strategies against heavy metal toxicity

Mercury (Hg), arsenic (As), cadmium (Cd), lead (Pb) and other toxic heavy metals (HM) pose significant risks to the environment, negatively impacting the morpho-physiological and biological traits of plants. At present, toxic elements constitute a significant proportion of the food chain, exerting an impact on human health due to their mobility and biomagnification. The metal exclusion biological technique stands out for its robust performance, even when dealing with extremely low metal concentrations. Its eco-friendly nature and cost-effectiveness further enhance its value. Due to the exponential growth pattern of bacteria, these exhibit high metal persistence and are recommended for metal exclusion processes. Moreover, vacuoles like vesicles present in mycorrhizal fungi can hold extremely high levels of HM. Microbe-assisted phytoremediation primarily occurs through two mechanisms: through the direct provision of the essential nutrients and phytohormones, such as plant growth regulators, siderophores, enzymes, and mineral; or indirectly by modulating the metal detoxification process. This indirect mechanism involves microbes aiding in the accumulation and sequestration of metals in plants through the secretion of specific extracellular substances like organic acids, biosurfactants, and chelators. Moreover, the metal bioavailability and translocation in the rhizosphere are also altered via various mechanisms like acidification, precipitation, complexation or redox reactions. The understanding of the molecular and physiological processes underpinning the functions of arbuscular mycorrhizal fungi (AMF) in reducing HM toxicity, improving plant performance by procuring nutrients under HM-toxicity has significantly improved in recent years. In this review, adaptive and persistent methods related to physiological and cross-protective mechanisms in bacteria and mycorrhizal fungi (MF) resulting from the evolutionary consequences of dealing with HM toxicity have been addressed. Furthermore, the article offers details on the physiological and molecular reactions of host plants with fungi, and bacteria to HM stress, which may be useful for unveiling new knowledge about the strategies of HMs remediation.