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Bioremediation of heavy metal-contaminated soil using metal-resistant microbes is a promising remediation technology. However, as exogenous bacteria sometimes struggle to survive and grow when introduced to new soils, it is important to develop appropriate carriers for microbial populations. In this study, we report a novel approach to remediating Cd-contaminated rice paddy soil using biochar-supported microbial cell composites (BMCs) produced from agricultural waste (cornstalks). Pot experiments showed that amendment with BMC was more efficient at reducing root and grain Cd content than pure bacteria, while improving soil Cd fractionation toward more stabilized and less labile forms. Bacteria in the BMC medium grew more readily with more abundant metabolites than those raised in free cells, probably because biochar provides shelter via porous structures (as confirmed by scanning electron microscopy) as well as additional nutrients. Overall, the improved long-term production of microbial biomass caused by BMC inoculation results in a higher remediation efficiency. Our results demonstrate the feasibility of using biochar as an appropriate carrier for metal-tolerant bacteria to remediate Cd-contaminated paddy fields., (Copyright © 2020 Elsevier Ltd. All rights reserved.)

Biological soil crusts (BSCs), which are ubiquitous in paddy fields, are known to remove pollutants from paddy fields systems. The Nano-TiO 2 enhanced the removal of Cd(II) by BSC under acidic irrigation water was found, and its mechanism was investigated. After the addition of nano-TiO 2 , the Cd(II) removal efficiency of BSC S increased by 26.70% than that of pure BSCs, and the Nano-TiO 2 induced faster removal velocity as well. Zeta potential and potentiometric titration results revealed that BSCs generated more negative charges and sites concentration after addition of Nano-TiO 2 at acidic environment. The carboxyl and amino/hydroxyl groups were the main functional groups on BSC and the BSC + TiO 2 . The higher concentration of amino/hydroxyl groups in BSC + TiO 2 (0.33 ± 0.08 mmol/g) was present than that of pristine BSCs (0.62 ± 0.02 mmol/g), and they were with similar concentration of phosphate groups and carboxyl groups. This result was attributed to the Nano-TiO 2 stimulated the BSCs to produce more extracellular polysaccharides and proteins. Our findings would provide novel strategy for the removal of cadmium from acidic irrigation water., Competing Interests: Declaration of Competing Interest We declare that we have no financial and personal relationships with other people or organizations that can inappropriately influence our work, there is no professional or other personal interest of any nature or kind in any product, service and/or company that could be construed as influencing the position presented in, or the review of, the manuscript entitled., (Copyright © 2019. Published by Elsevier B.V.)

Bioremediation of heavy metal polluted soil using metal-resistant bacteria has received increasing attentions. In the present study, we isolated a heavy metal-resistant bacterial strain from a Cd-contaminated soil, and conducted pot experiments to evaluate the effect of bacterial inoculation in soil on soil Cd speciation, rice grain biomass and Cd accumulation. We find that the isolated bacterial strain is a Gram-negative bacterium, and named as Delftia sp. B9 based on the 16S rDNA gene sequence analysis. TEM-EDS manifests that Cd can be bioaccumulated inside cell, resulting in intracellular dissolution. The Cd contents of rice grain in the two rice cultivars (early and late rice) are all below the standard limit for Food Safety of People's Republic of China (0.2 mg/kg) after the treatment of both living and non-living cells. Non-living cells are more applicable than the use of living cells for the short time bioremediation. The average content of soil exchangeable fraction of Cd decreases whereas the residual fraction increases with bacterial inoculation. All our results suggest Delftia sp. B9 is able to the stabilization of Cd in soil and reduce Cd accumulation in rice grain, therefore, this strain is potentially suitable for the bioremediation of Cd-contaminated paddy soils., (Copyright © 2018 Elsevier Inc. All rights reserved.)