Synergism of Phosphate-solubilizing microoranisms-plant

interactions for bioremediation of metalliferous soils

We hope to establish a sustainable, regulable and reusable project to solve the soil polluted by heavy metals. Phosphate-solubilizing bacteria have important functions. In our project, we used the mechanism of the alliance between microbe and plant, by manufacturing Bacillus megaterium, which is a kind of phosphate-solubilizing microorganism exists in the root system, forcing it enhance the plant remediation from two aspects, accumulating heavy metals and defend adversity stress. To achieve the goal of spatial specificity, we make most of the expression system which is regulated by root organic acid. We also used MBP (metal binding protein) and ACC deaminase to make accumulation of heavy metal in root system’s soil success. Finally, heavy metals will transfer to plant itself. A series of transformation we made in phosphate-solubilizing bacteria in our project will solve the weakness of hyper-accumulators, therefore, the remediation method will be put into use widely.

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. 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.

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.

   Phosphorus is the second important key element after nitrogen as a mineral nutrient in terms of quantitative plant equirement. However, plants can use only a small amount of this P since 75–90% of added P is precipitated by metal–cation complexes, and rapidly becomes fixed in soils. In this regard, phosphate solubilizing microbes are considered as the most efficient and eco-friendly means for phytoremediation of metalliferous soils. Although, several bacterial strains have been identified as PSB their performance under in situ conditions is not reliable. Therefore,we genetically engineered our chassis B. megaterium as a new strategy to accelerate phytoremediation process.

In our project, the circuit uses a genetic ‘toggle switch’ architecture in which reciprocal repression by the LacI and TetR transcription factors form transcription states that are maintained by the circuit’s linked feedback loops. Inhibition of TetR expression by anhydrotetracy-cline (ATc), a compound that is not normally found in nature, is necessary for expression of LacI. Removal of ATc from the environment activates the expression of TetR, which leads to cell death.