Introduction heavy metal pollution

FUTURE RESEARCH DIRECTIONS
Isolation of various plants associated microbes and characterization of its beneficial metabolites/processes are time consuming, since it requires the analysis of more than thousands of isolates. Thus strong molecular research effort is required in order to find specific biomarker associated with the beneficial microbes for efficient microbe assisted bioremediation. Although promising results have been reported under laboratory conditions, showing that inoculation of beneficial microbes particularly plant growth promoting bacteria and/or mycorrhizae may stimulate heavy phytoextraction or phytostabilization. Only a few studies have demonstrated the effectiveness of the microbial assisted plant bioremediation of pesticides and toxic metals in field conditions (Brunetti et al., 2011; Juwarkar and Jambhulkar, 2008; Wu et al., 2011a; Yang et al., 2012). Genetically engineered organisms with novel pathways will to generate new or improved activities hold a great potential for enhanced bioremediation. Using genes encoding the biosynthetic pathway of bio-surfactants can enhance biodegradation rates by improving the bioavailability of the substrates and genes encoding resistance to critical stress factors may enhance both the survival and the performance of designed catalysts. Thus, genetic engineering of indigenous microflora, well adapted to local environmental conditions, may offer more efficient bioremediation of contaminated sites and making the bioremediation more viable and eco-friendly technology. Complete genome sequences for several environmentally relevant microorganisms, mechanism of pesticide solubility, uptake and availability of nutrients/ pesticides, signalling processes that occur between plant roots and microbes, these types of analysis will surely prove useful for exploring the mechanism of pollutants-microbes-plant interactions. Moreover, such knowledge may enable us to improve the performance and use of beneficial microbes as inoculants for microbial bioremediation.

Emphasis should be placed when developing bioremediation systems using plant-associated bacteria, to choose wild type bacteria, or bacteria enhanced using natural gene transfer, to avoid the complications of national and international legislation restricting and monitoring the use of genetically modified microbes (GMMs). However, with a global political shift towards sustainable and green bioremediation technologies, the use of plant-associated bacteria to degrade toxic synthetic organic compounds in environmental soil may provide an efficient, economic, and sustainable green remediation technology for future environment (Bhatia and Malik, 2011).

Much is still unknown about tolerances, degradative capacities and ecological interactions of organisms that have potential use in eco-restoration. However, it is clear, that plants and microbes act cooperatively to improve the rates of biodegradation and biostabilization of environmental contaminants as well as improve nutrient contents in degraded lands.. Knowledge of the microbial community structure resident to the rhizosphere of plants that are resistant to a given contaminant will improve the chances of successfully increasing biodegradation rates when co-inoculating plants and microbes into contaminated environments. In designing a eco-restoration program the oxidative capacity of a plant should be considered in terms of its action on the contaminant itself and for its potential to support rhizospheric microbes with the capacity to enhance biodegradation. Additional basic biological and ecological information in these areas will allow us to make better informed decisions on how to widen bottlenecks in bioremediation/eco-restoration processes (Cohen et al. 2004).