Metal-immobilizing Serratia liquefaciens CL-1 and Bacillus thuringiensis X30 increase biomass and reduce heavy metal accumulation of radish under field conditions.

In this study, metal-tolerant bacteria Serratia liquefaciens CL-1 and Bacillus thuringiensis X30 were compared for their Cd and Pb immobilization in solution and impacts on biomass and Cd and Pb uptake in a radish in metal-contaminated soils under field conditions. Strains CL-1 and X30 significantly reduced water-soluble Cd and Pb concentrations (45-67%) and increased the pH in solution compared to the controls. These strains significantly increased the biomass (25-99%) and decreased edible tissue Cd and Pb uptake in the radish (37-81%) and DTPA-extractable Cd and Pb contents (18-44%) of the rhizosphere soil compared to the un-inoculated controls. Strain CL-1 had higher potential to reduce edible tissue Cd and Pb uptake in the radish and DTPA-extractable Cd content than strain X30. Also, these strains significantly increased Cd translocation factor and strain CL-1 also significantly increased Pb translocation factor of the radish. Furthermore, strain CL-1 significantly increased the ratio of small soil aggregates (< 0.25 mm and 0.25-0.50 mm) of the rhizosphere soil. The results showed that these strains reduced the edible tissue Cd and Pb uptake through decreasing Cd and Pb availability in the soil and increasing Cd or Pb translocation from the roots to the leaves of the radish. The results also suggested the bacteria-related differences in reduced heavy metal uptake in the radish and the mechanisms involved under field conditions.

Han H ，Sheng X ，Hu J ，He L ，Wang Q ... -  《-》

Metal-immobilizing and urease-producing bacteria increase the biomass and reduce metal accumulation in potato tubers under field conditions.

In this study, the effect of two metal-immobilizing bacterial strains, Serratia liquefaciens CL-1 and Bacillus thuringiensis X30, on the availability of Cd and Pb and the metal accumulation in potato tubers, as well as the underlying mechanisms in metal-contaminated soils were characterized. Moreover, the impacts of the strains on metal immobilization, pH, and NH4+ concentration in metal-contaminated soil solutions were evaluated. Strains CL-1 and X30 increased tuber dry weight by 46% and 40%, reduced tuber Cd and Pb contents by 68-83% and 42-47%, and decreased the Cd and Pb translocation factors by 61-70% and 30-34%, respectively, compared to the controls. Strains CL-1 and X30 decreased the available Cd and Pb contents by 52-67% and 30-44% and increased the NH4+ content by 55% and 31%, pH, urease activity by 70% and 41%, and relative abundance of ureC gene copies by 37% and 20% in the rhizosphere soils, respectively, compared with the controls. Reduced Cd and Pb concentrations and increased pH and NH4+ concentration were found in the bacteria-inoculated soil solution compared to the controls. These results suggested that the strains reduced tuber metal uptake through decreasing the metal availability and increasing the pH, ureC gene relative abundance and urease activity as well as decreasing the metal translocation from the leaves to tubers. These results may provide an effective metal-immobilizing bacteria (especially strain CL-1)-enhanced approach to reduce metal uptake of potato tubers in metal-polluted soils.

Cheng C ，Han H ，Wang Y ，He L ，Sheng X ... -  《-》

Increased biomass and reduced rapeseed Cd accumulation of oilseed rape in the presence of Cd-immobilizing and polyamine-producing bacteria.

Two Cd-immobilizing and polyamine-producing bacteria Serratia liquefaciens CL-1 and Bacillus thuringiensis X30 were characterized for their effects on Cd immobilization, pH, and polyamine production in the solution and the rapeseed biomass and Cd uptake of Brassica napus Qinyou-10 in Cd-contaminated soil. These strains significantly increased pH and reduced water-soluble Cd concentration (25-76%) compared to the controls. Furthermore, strain CL-1 produced more polyamine (71-192%) in the solution than strain X30. Cell surface absorbed Cd content was increased by 23-56% in the presence of strain CL-1 compared to strain X30. The strains significantly increased the rapeseed biomass (12-32%), pH, polyamine content (70-244%), and relative abundance (21-49%) of arginine decarboxylase-producing bacteria (ADPB) of the rhizosphere soils but decreased DTPA-extractable Cd content and rapeseed Cd uptake compared to the controls. Notably, strain CL-1 had higher ability to reduce the rapeseed Cd and DTPA-extractable Cd contents and increase the abundance of ADPB than strain X30. Our results showed the distinct impact of these strains on the rapeseed Cd uptake and available Cd content and suggested that these strains reduced the available Cd and rapeseed Cd uptake by increasing the cell adsorption of Cd, abundance of ADPB, polyamine production, and pH in the rhizosphere soils.

Han H ，Wang Q ，He LY ，Sheng XF ... -  《-》

Effects of Bacillus thuringiensis HC-2 Combined with Biochar on the Growth and Cd and Pb Accumulation of Radish in a Heavy Metal-Contaminated Farmland under Field Conditions.

Li Z ，Wang P ，Yue X ，Wang J ，Ren B ，Qu L ，Han H ... -  《-》

Heavy metal-immobilizing bacteria increase the biomass and reduce the Cd and Pb uptake by pakchoi (Brassica chinensis L.) in heavy metal-contaminated soil.

Microbial immobilization is a novel and environmentally friendly technology that uses microbes to reduce metal availability in soil and accumulation of heavy metals in plants. We used urea agar plates to isolate urease-producing bacteria from the rhizosphere soil of pakchoi in Cd- and Pb-contaminated farmland and investigated their effects on Cd and Pb accumulation in pakchoi and the underlying mechanisms. The results showed that two urease-producing bacteria, Bacillus megaterium N3 and Serratia liquefaciens H12, were identified by screening. They had higher ability to produce urease (57.5 ms cm-1 min-1 OD600-1 and 76.4 ms cm-1 min-1 OD600-1, respectively). The two strains allowed for the immobilization of Cd and Pb by extracellular adsorption, bioprecipitation, and increasing the pH (from 6.94 to 7.05-7.09), NH4+ content (69.1%-127%), and NH4+/NO3- ratio (from 1.37 to 1.67-2.11), thereby reducing the DTPA-extractable Cd (35.3%-58.8%) and Pb (37.8%-62.2%) contents in the pakchoi rhizosphere soils and the Cd (76.5%-79.7%) and Pb (76.3%-83.5%) contents in the leaves (edible tissue) of pakchoi. The strains were highly resistant to heavy metal toxicity; produced IAA, siderophores and abscisic acid; and increased the NH4+/NO3- ratio, which might be related to the two strains protectiing pakchoi against the toxic effect of Cd and Pb and increasing pakchoi biomass. Thus, the results were supposed to strain resources and a theoretical basis for the remediation of Cd- and Pb-contaminated farmlands for the safe production of vegetables.

Han H ，Cai H ，Wang X ，Hu X ，Chen Z ，Yao L ... -  《-》