Co-inoculation effects of B. licheniformis and P. aeruginosa on soil Cd and As availability and rice accumulation.

There have been studies reporting the effects of multiple bacterial strains on the Cd/As immobilization and transformation in culture media. However, there is limited research to validate the effects of microbial strain combination on plant Cd/As accumulation and antioxidant system in the soil-plant system. By planting the rice (Zhefu 7) with the co-inoculation of bacterial strains (i.e. Bacillus licheniformis and Pseudomonas aeruginosa) after two months with the contaminations of Cd (2 mg/kg), As (80 mg/kg) and Cd + As (2 + 80 mg/kg), we found that the bacterial co-inoculation decreased Cd concentrations in the rhizosphere soil porewater, but had limited effects on mitigating plant Cd accumulation. By contrast, the co-inoculation did not affect the As(III) and As(V) concentrations in the rhizosphere soil porewater, but decreased As(III) and As(V) concentrations by 17% and 17% in the root respectively and by 17% and 37% in rice shoot respectively. Using DNA sequencing, we found the increased abundance in both exogenous Bacillus licheniformis and native microorganisms, indicating that the added strains had synergetic interactions with soil native microorganisms. Regarding on plant antioxidant enzyme system, the bacterial co-inoculation decreased the concentrations of superoxide dismutase (SOD), hydrogen peroxide (H2O2) and malondialdehyde (MDA) by 75%, 74% and 22%, mitigating the As damage to rice root and promote plant growth. However, under Cd and As co-stress, the effects of co-inoculation on mitigating plant As accumulation and enhancing plant stress resistance appear to be diminished. Our findings underscore the importance of microbial co-inoculation in reducing plant As accumulation and preserving plant health under heavy metal stress.

Machine-learning-facilitated prediction of heavy metal contamination in distiller's dried grains with solubles.

Excessive heavy metal contamination often occurs in feed due to natural or anthropogenic activity, leading to poisoning and other health problems in animals. In this study, a visible/near-infrared hyperspectral imaging system (Vis/NIR HIS) was used to reveal the different characteristics of spectral reflectance of Distillers Dried Grains with Solubles (DDGS) doped with various heavy metals and to effectively predict metal concentrations. Two types of sample treatment were used, namely tablet and bulk. Three quantitative analysis models were constructed based on the full wavelength, and through comparison the support vector regression (SVR) model was found to show the best performance. As typical heavy metal contaminants, copper (Cu) and zinc (Zn) were used for modeling and prediction. The prediction set accuracy of the tablet samples doped with Cu and Zn was 94.9% and 86.2%, respectively. In addition, a novel characteristic wavelength selection model based on SVR (SVR-CWS) was proposed to filter characteristic wavelengths, which improved the detection performance. The regression accuracy of the SVR model on the prediction set of tableted samples with different Cu and Zn concentrations was 94.7% and 85.9%, respectively. The accuracy of bulk samples with different Cu and Zn concentrations was 81.3% and 80.3%, respectively, which indicated that the detection method can reduce the pretreatment steps and verify its practicability. The overall results suggested the potential of Vis/NIR-HIS in the detection of feed safety and quality.

Bacterial coculture enhanced Cd sorption and As bioreduction in co-contaminated systems.

The bacterial interactions that regulate Cd sorption and As bioreduction in co-contaminated systems are poorly understood. We isolated two bacterial strains, i.e., Pseudomonas aeruginosa and Bacillus licheniformis from a Cd and As co-contaminated soil and compared the effects of monoculture and coculture on microbial Cd sorption and As bioreduction efficiency in the media with different Cd (0, 0.5, 5, 10, 50, 100 mg/L) and As(Ⅴ) (0, 90 mg/L) concentrations. Compared with monoculture, the bacterial coculture increased the Cd sorption efficiency by up to 32% and the As bioreduction (As(Ⅴ) to As(Ⅲ)) efficiency by up to 28%, associated with the increased abundance of As reduction gene arsB. Based on SEM-TEM and metabolomics, the enhanced efficiency was attributed to bacterial interactions, supported by the differential secretion of extracellular polymeric substances. Notably, the differential lipids and lipid-like molecules, and organoheterocyclic compounds resulted from bacterial interactions compared to monoculture exhibited the highest Cd sorption and As bioreduction. The increased efficiencies by bacterial coculture were verified by soil incubation experiments. These results provide insight on applying specific bacterial coculture and their metabolites to enhance Cd sorption and As bioreduction in effective and sustainable remediation of co-contaminated environments.

Alkaline lignin does not immobilize cadmium in soils but decreases cadmium accumulation in the edible part of lettuce (Lactuca sativa L.).

Heavy metal contamination and low use efficiency of phosphorus (P) fertilizers are worldwide issues. Alkaline lignin is expected to decrease the heavy metal risk and enhance the P availability in heavy-metal-contaminated soils. A 120-day incubation study examined the effects of alkaline lignin on Cd, Pb and P bioavailability and transformation in Cd or Cd/Pb co-contaminated red and cinnamon soils and elucidated the associated mechanisms. A pot experiment further tested Cd accumulation in lettuce (Lactuca sativa L.) grown in the Cd-contaminated red soil. The amendment of alkaline lignin increased the concentrations of bioavailable Cd by 13-20% in the acid red soil and 97-107% in the alkaline cinnamon soil, respectively, due to the increase of dissolved organic C concentrations. Meanwhile, it also increased the concentrations of available P in both soils, Al-P in the red soil and Ca2-P in the cinnamon soil. Consequently, alkaline lignin amendment increased lettuce biomass of shoots by 8-23% and of roots by 56-71%, P uptake by 37-50% in shoots and by 28-62% in roots, and limited Cd transport from root to shoot which decreased Cd concentrations by 26% in lettuce shoot (edible part). The results suggest that alkaline lignin increases plant growth and decreases Cd bioaccumulation in the shoot through restricting Cd translocation from the root to shoot and increasing soil P availability but not Cd immobilization, and hence may have potential to reduce vegetable Cd contamination risk.