Application Of Endophytic Bacterium Isolated From Cd Hyperaccumulator Solanum Nigrum L For Phytoremediation Enhancement

Phytoremediation which engaging hyperaccumulating plants to extract heavy metals has recently been proposed as a promising way to remove toxicant from contaminated soils. The advantages of phytoremediation method include low-cost, solar-driven, in situ remediation, retains topsoil and less secondary waste generation. However, the wide application of phytoremediation for heavy metal has been restricted due to its disadvantages such as only seasonally effective and too slow. It is necessary to search for the ways to enhance the phytoremediation capacity of plants using microorganism or chemistry control methods.The application of plant-endophyte symbiotic system is proposed to be a potential technique to improve efficiency of phytoremediation. In the last few years, lots of research clearly demonstrate the utility of using natural endophytes or engineered endophytes to enhance phytoremediation of organic pollutants. However, the studies on natural or engineered endophytic bacteria for improving phytoremediation of heavy metals has been delayed because of the lack of valuable strains conferring the capacity for heavy metal resistance and detoxification. The objective of this study was to obtain such valuable strain from hyperaccumulator and to evaluate its potential role on heavy metal phytoremediation.In this study, endophytic bacterium LRE07 was isolated from cadmium hyperaccumulator Solanum Nigrum L. It was identified as Serratia sp. by 16S rRNA sequence analysis. The endophyte was evaluated in relation to its potential for plant growth promotion by investigated indoleacetic acid (IAA) production, mineral phosphate solubilization and siderophore production. The result showed that the isolate had ability to solubilize mineral phosphate and produce indole acetic acid, siderophore and ACC deaminase. The characters mentioned above indicate the potential role of the endophyte for increasing the biomass of its host plant. The strain also exhibited different multiple heavy metal resistance characteristics. The minimal inhibitory concentration (MIC) of the strain in the liquid LB medium containing heavy metal ions was 10mM (Cu²⁺), 8mM (Cd²⁺), 12mM (Cr⁶⁺), 4mM (Pb²⁺) and 5mM (Zn²⁺), respectively. The heavy metal detoxification was studied in growing LRE07 cells. After 72h, it bound over 65% of cadmium and 35% of zinc in its growing cells from single metal solution while nearly no sorption of copper, lead or chromium was observed. An analogous removal phenomenon occurred in multi-ions system except lead. Pot tests showed that endophyte LRE07 was able to enhance plant growth and improved the efficiency of heavy metal accumulation of its host plant. The result of this study proved the feasibility of the application of plant-endophyte symbiotic system to improve efficiency of phytoremediation.