Metal resistant and phosphate solubilizing bacterium improves maize (Zea mays) growth and mitigates metal accumulation in plant

Synergistic Effect of Biochar, Phosphate Fertilizer, and Phosphorous Solubilizing Bacteria for Mitigating Cadmium (Cd) Stress and Improving Maize Growth in Cd-Contaminated Soil

Cadmium (Cd) contamination threatens human health and plant growth due to its accumulation in edible parts. The sole application of phosphorus-solubilizing bacteria (PSB), biochar (BC), and phosphorus (P) effectively mitigates Cd's adverse effects in contaminated agricultural systems. However, further investigation into their combined impacts on Cd toxicity and maize (Zea mays) production is essential. This study evaluates the synergistic effects of PSB (10 g kg-1 of Bacillus megaterium), BC (5% w/w), and P (0.8 g kg-1) on soil properties and the morphological and physiological traits of maize cultivated in agricultural soil contaminated with Cd (20 mg kg-1). The study revealed that Cd toxicity negatively impacts soil properties, reducing shoot and root biomass, lowering chlorophyll content, and heightening oxidative stress levels. Conversely, the combined use of P, PSB, and BC markedly improved soil properties, increasing the organic matter by 175.94%, available K by 87.24%, and available P by 306.93% compared to the control. This combination also improved maize growth metrics, with increases in aboveground dry biomass (92.98%), root dry biomass (110.33%), chlorophyll a (28.20%), chlorophyll b (108.34%), and total chlorophyll (37.17%). Notably, the treatment reduced Cd concentrations in maize leaves by 61.08% while increasing soil Cd levels by 31.12% compared to the control group. Overall, the synergistic effect of P-BC-PSB is an eco-friendly strategy for mitigating Cd toxicity in contaminated soil. However, further studies are required to explore its effects and molecular mechanisms on other crops.

Improving radish phosphorus utilization efficiency and inhibiting Cd and Pb uptake by using heavy metal-immobilizing and phosphate-solubilizing bacteria

Phosphate-solubilizing bacteria play a key role in increasing plant growth as potential suppliers of soluble phosphorus and have great potential for the remediation of heavy metal-polluted soils. However, the soil and microbiological mechanisms by which phosphate-solubilizing bacteria prevent heavy metal absorption in radish have not been adequately studied. Here, the mechanisms of phosphorus solubilization, Cd and Pb immobilization, and the inhibition of heavy metal absorption by phosphate-solubilizing bacteria were studied in radish through solution adsorption and pot experiments. Two phosphate-solubilizing bacteria with high Cd and Pb removal rates (46.9-97.12 %), Klebsiella sp. M2 and Kluyvera sp. M8, were isolated. The soluble phosphorus content released by strains M2 and M8 was 265-277 mg L^-1, achieved by secreting oxalic acid, ascorbic acid, citric acid, and succinic acid in an inorganic phosphorus medium containing 3 mg L^-1 Cd and 5 mg L^-1 Pb. Furthermore, these two functional strains induced the formation of Pb₂(PO₄)₂, Cd(PO₃)₂, Fe₂Pb₃(PO₄)₂, CdS, and PbS precipitates that immobilized Cd and Pb in the solution. In general, strains M2 and M8 inhibited the absorption of Cd and Pb by radish by the following mechanisms: i) bacterial cell wall adsorption, ii) induction of Pb₂(PO₄)₂, Cd(PO₃)₂, Fe₂Pb₃(PO₄)₂, CdS, and PbS precipitation in the solution/soil, iii) increases in the Ca₂P and FeP contents in the radish rhizosphere, and iv) the promotion of bacterial community enrichment toward phosphorus-solubilizing and plant growth-promoting properties (Ramlibacter, Enterobacter, Bacillus, Gemmatimonas, and Lysinibacillusin) in the radish rhizosphere. These results provide bacterial resources and technical approaches to heavy metal pollution amelioration and efficient phosphorus fertilizer use in farmland.

Modeling and Cr(VI) ion uptake kinetics of Sorghum bicolor plant assisted by plant growth-promoting Pannonibacter phragmetitus: an ecofriendly approach

The research work focuses on the application of Cr(VI)-resistant plant growth-promoting bacteria Pannonibacter phragmetitus for enhancing Cr(VI) uptake by Sorghum bicolor. Significant increase in plant shoot and root characters was found when assisted by P. phragmetitus. The obtained strain showed 700 mg/L of chromium reduction at 24-h incubation. Indole-3 acetic acid (IAA) production by the bacterial strain was found to be 86.45 μg/mL. Pannonibacter phragmetitus solubilized tricalcium phosphate showing maximum solubilizing activity of PSI = 3.31. The q_max of P. phragmetitus was high in the wavelength of 600 nm. Langmuir isotherm best described the Cr(VI) ion uptake by the plant. The R_L values reliably reduced with expanding Cr(VI) ion concentration from 25 to 150 mg/L. The outcomes of kinetic studies showed that compared with pseudo first-order, pseudo second-order kinetics better describes the plant Cr(VI) uptake rate. Elovich model describes the increased rates for attaining equilibrium. The equilibrium parameter values for different Cr(VI) ion concentrations range between 0 and 1 which describes the favorable condition for plant metal uptake at different concentrations. Graphical abstract.