Endophytic Bacterium Isolated From Hyperaccumulator Phytolacca Acinosa Roxb. For Promotion Heavy Metal Phytoremediation Of Sweet Sorghum

Heavy metal pollution by industrial activities and technological development is posing significant threats to the environment and public health. The permanent existences of cadmium (Cd (Ⅱ)), lead (Pb (Ⅱ)), copper (Cu (Ⅱ)) and chromium (Cr (Ⅳ)) in polluted ecosystems threaten the health of entire human beings all the time. Phytoremediation possesses the advantages of low-cost, solar-driven, in situ remediation, retains topsoil and less secondary waste generation. In recent years, the application of plant-endophyte symbiotic system is proposed to be a potential technique to improve efficiency of phytoremediation.On the other hand, due to a large number of promotion of bioenergy, the competition of agricultural resources between energy crop and food crop is one of the critical socioeconomic issues with the increasing use of biofuels.This dilemma could be bypassed through producing biofuel feedstocks on marginal land. Bacterial endophytes could be of great value in enabling energy plants to grow better on marginal land for promoting the production of biofuels stocks. Sweet sorghum (Sorghum bicolor L.) is one of the most drought resistant energy crops, and equipped with higher biomass yield and photosynthetic efficiency and lower production costs. Sweet sorghum could also remove heavy metals from soil. Therefore, sweet sorghum is a good candidate for biofuel feedstocks production and phytoremediation.In this study, plant growth promoting endophyte (PGPE) Bacillus sp. SLS18was isolated from Mn hyperaccumulator Phytolacca acinosa Roxb. The effects of PGPE SLS18on the biomass production and Mn/Cd-uptake of sweet sorghum (Sorghum bicolor L.), Phytolacca acinosa Roxb. and Solanum nigrum L. were investigated. SLS18displayed multiple heavy metals and antibiotics resistances. The strain also exhibited the capacity of producing indole-3-acetic acid, siderophores and1-aminocyclopropane-1-carboxylic acid deaminase. In pot experiments, SLS18could not only infect plants effectively, but also significantly increase the biomass of the three tested plants in the presence of Mn/Cd.The promoting effect order of SLS18on the biomass of the tested plants was sweet sorghum> P. acinosa> S. nigrum L. In the presence of Mn (2000mg kg-1) and Cd (50mg kg-1) in vermiculite, the total Mn/Cd-uptakes in aerial part of sweet sorghum, P. acinosa and S. nigrum L. were increased by65.2%/40.0%,55.2%/31.1%, and18.6%/25.6%, respectively, compared to the uninoculated controls. This demonstrates that the symbiont of SLS18and sweet sorghum has the potential of improving sweet sorghum biomass production and its total metals-uptake on heavy metal-polluted marginal land. It offers the potential that heavy metal-polluted marginal land could be utilized in planting sweet sorghum as biofuel feedstock for ethanol production, which not only gives a promising phytoremediation strategy, but also eases the competition for limited fertile farmland between energy crops and food crops.