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Revision as of 06:38, 11 August 2017
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Continued worldwide industrialization has caused extensive environmental and human health problems. A wide variety of chemicals, e.g., heavy metals, pesticides, chlorinated solvents, etc., have been detected in different natural resources such as soil, water, and air. Among the pollutants, the heavy metals are of concern to human health due to their cytotoxicity,mutagenicity, and carcinogenicity.
Soil polluted by heavy metals represent an important environmental problem due to the toxic effects of metals, their accumulations throughout the food chain and the additional risk of groundwater contamination.
Metal remediation through common physico-chemical techniques is expensive and unsuitable in the case of extensive areas. Therefore biotechnological approaches have received a great deal of attention in recent years. Bioremediaton, as a way of natural attenuation, adds phytoremediation, the use of plants for reclamation and microbe(PSB) together as a strategy for either enhancing uptake(PSB-assisted Phytoextraction) or reducing the bioavailability of metal contaminants(PSB-immobilized Phyto-promotion mechanism) in the soil, especially in the rhizosphere to accelerate plant biomass production and root enlongation.overvie
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Phytoextraction is based on the use of hyperaccumulator plants, which can tolerate and accumulate high concentration of metals. Ideal hyperaccumulators require the characteristics of deep rooted, rapid growth and a high amount of biomass. In fact, many hyperaccumulators are slow in growth, produce low bow biomass and cannot grow in metal-stress soil. Further, the overproduction of ethylene in response to metal-stress leads to inhibition of root growth, root hair formation and consequently development of the plant as a whole. Therefore, in our project we took advantage of co-expression of ACC deaminase and iaaM genes in our chassis PSB(B. megaterium) to enhance plant growth and biomass by P solubilization and uptake particularly under stress condition by heavy metals. Meanwhile, we also exploited bacterial chemotaxis, McfS, a multiple chemoreceptor from strain P. putida F1 to detect response of organic acids secreting in the rhizosphere.
PSB-assisted Phytoextraction(ex situ)
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In this module, our team designed a pathway that the Pb ions will bind to PbR protein when activated ions are in the soil environment. It induces downstream gene expression, and results in the tetR protein inhibition promoter PltetO1 expression. At the same time, the strong promoter P43 of B.megaterium stimulated the expression of MBP in the downstream lead-producing peptide. It makes the chelating peptide of Pb metal, which reduced the total amount of heavy metals in the soil to be harmless level. When there is no Pb ions presented in the environment, the expression of tetR was blocked and the inhibition of PltetO1 was released. It results in the lacI repressor binding to the lacO sequence, and leads to blocking the expression of MBP. This mechanism is effective in preventing the infinite expression of MBP against the B. megaterium itself.
PSB-immobilized Phyto-promotion
