Unveiling the performance of a novel alkalizing bacterium Enterobacter sp. LYX-2 in immobilization of available Cd

Simultaneous Cd immobilization and oxidative stress alleviation in Brassica chinensis by a novel phosphate-solubilizing strain Sutcliffiella horikoshii P1

Microbial remediation of cadmium (Cd) pollution offers economically green and operationally simple advantages, particularly in environments with mild contamination. The acquisition of efficient strains and coupling between bacterial response and plant fitness are current research emphases in the remediation process. In this study, a novel phosphate-solubilizing strain with outstanding Cd-resistance, Sutcliffiella (S.) horikoshii P1 was isolated. Cd removal efficiency reached 98.85 % by the strain within 24 h at an initial concentration of 5 mg/L. Distribution analysis revealed that the dominant mechanism of Cd removal by the strain varies with Cd concentrations. Notably, the seed soaking of Brassica chinensis with S. horikoshii P1 could improve seed germination rate and growth potential regardless of the presence of Cd stress. Morphological and biochemical trait analysis revealed that the inoculated strain also increased fresh weight and reduced the Cd phytoavailability of Brassica chinensis by producing active substances and alleviating plant oxidative stress. Pot experiment demonstrated that the transport factor (TF) and bioconcentration factor (BCF) decreased by 22.76 % and 33.59 %, respectively, and Cd content in edible parts met food safety standards. Whole-genome sequencing analysis demonstrated that functional genes related to heavy metal resistance and transport (cadC, czcD, znuA, etc.), and gene clusters involved in siderophore secretion may regulate Cd immobilization and the plant growth-promoting effect of S. horikoshii P1. The results underscored the feasibility and effectiveness of Sutcliffiella horikoshii in addressing Cd contamination and promoting plant growth, providing a basis for the future application in agricultural safe production.

Phylogenetic distance drives rare cooperation in a competition-dominated cadmium stress environment

Microbial interactions profoundly influence community structure and offer innovative strategies for heavy metal removal. However, the mechanisms driving competition and cooperation among microbes under cadmium (Cd) stress remain unclear. In this study, we analyzed 4851 pairwise interactions among 99 bacterial strains in a Cd-containing environment with direct experimental data, revealing that over 50% of these interactions were dominated by competition with cooperation occurring infrequently (14.29%). Intriguingly, cooperative behavior arose more frequently between genetically distant strains or those with limited individual Cd adsorption capabilities. It also showed no spike in cooperation when bacteria from the same soil were screened. Notably, we identified a synergistic interaction between two bacteria species based on genetically distant and growth-promoting properties that colonize rice roots, providing both Cd remediation and probiotic benefits. In comparison to monoculture, co-culture enhanced cadmium absorption by 50.80% and 91.60%, respectively. The leaf Cd content in single- and coculture-strain treatment groups exhibited significant reductions of 65.73%, 67.60%, and 70.40%, respectively. Furthermore, a 37.10% elevation in chlorophyll content was observed in the dual-strain treatment group relative to the single-strain treatment group. This study underscores the potential of designing microbial consortia by leveraging genetic diversity and interaction dynamics to enhance heavy metal immobilization, promote crop productivity and environmental sustainability.

Surface display of CadR protein on Rhodopseudomonas palustris CGA009 for enhanced heavy metal bioremediation

Heavy metal pollution poses significant ecological and public health risks, and surface display engineering shows promise for bioremediation in this area. Although anoxygenic photosynthetic purple nonsulfur bacteria (PNSB) have been effectively applied to degrade pollutants due to their metabolic versatility, the use of surface display technology in PNSB remains very limited. In this study, we constructed a surface display system using Rhodopseudomonas palustris CGA009 as the host. The metal-binding protein CadR was fused with outer membrane protein A (OmpA) and expressed in CGA009. SDS-PAGE and immunofluorescence analysis identified the successful expression of the fusion protein on the cell surface. In addition, we used flow cytometry to explore the enhancement effects of linker peptides and different promoters on surface display efficiency under different light intensities. The surface display system enhanced the heavy metal resistance of the host bacteria, and the maximum removal rate of Cd2 + reached 95.6 %. By means of Langmuir isotherm analysis, the maximum biosorption capacity of the system for Cd2+ is 101.11 mg/g. The system demonstrates feasibility for application in complex real-world environmental samples. The presence of various metal ions does not interfere with the system's specific adsorption of Cd²⁺. It can stably maintain an adsorption efficiency of over 80 % under conditions of pH 6-8, temperatures of 20-35°C, and light intensity of 1000-6000 lux. Additionally, the system achieves a removal efficiency of 94.3 % in Cd wastewater. In summary, this study provides a reference for the development of photosynthetic bacterial surface display systems and provides an advanced bioremediation strategy for heavy metal contaminated wastewater.

Statistical modelling, optimization, and mechanistic exploration of novel ureolytic Enterobacter hormaechei IITISM-SA3 in cadmium immobilization under microbial inclusive and cell-free conditions through microbially induced calcite precipitation

The study aimed to evaluate the potential of a novel isolated ureolytic Enterobacter hormaechei IITISM-SA3 in cadmium bioremoval through MICP. The optimization and modelling of the biotic and abiotic factors affecting the process of mineralization were also performed. In addition, the underlying mechanism of MICP-driven Cd mineralization under microbial-inclusive and cell-free conditions was revealed and supported through the characterization of the bio-precipitates obtained using various characterization techniques. The results indicated that the isolate could remove 97.18% Cd2+ of 11.4 ppm under optimized conditions of 36.86 h, pH 7.63, and biomass dose of 1.75 ml. Besides, the presence and absence of bacterial cells were found to influence both the morphologies and crystalline structures of precipitates. The precipitates obtained under microbial-inclusive conditions showed typical rhombohedral crystalline structures of the composition comprising CaCO3, CdCO3, and 0.67Ca0.33CdCO3. However, the crystalline nature of the precipitate reduced to a nano-sized granular structure in cell-free media. Unlike the cadmium mineralization process under microbial-inclusive media, where bacterial cells serve as nucleation sites for crystallization, the carbonate precipitation effectively captures Cd2+ through co-precipitation, chemisorption, or alternative mechanisms involving interactions between metal ions and CaCO3 under cell-free conditions. The findings presented suggest that using cell-free culture supernatant enriched with carbonate ions provides an avenue that could be harnessed for sustainable metal remediation.

Adsorption mechanism of Cd2+ on microbial inoculant and its potential for remediation Cd-polluted farmland soils

The adsorption characteristics and mechanism of Cd2+ on microbial inoculant (MI) mainly composed of Bacillus subtilis, Bacillus thuringiensis and Bacillus amyloliquefaciens, and its potential for remediation Cd polluted soils through batch adsorption and soil incubation experiments. It was found that the Freundlich isotherm model and the pseudo-second-order kinetics were more in line with the adsorption processes of Cd2+. The maximum adsorption capacity predicted by Langmuir isotherm model suggested that of MI was 57.38 mg g-1. Scanning electron microscopy and energy dispersive spectroscopy (SEM-EDS) images exhibited the surface structure of MI was damaged to varying degrees after adsorption, and Cd element was distributed on the surface of MI through ion exchange. X-ray diffraction (XRD) results showed that CdCO3 was formed on the surface of MI. Moreover, the functional groups (-OH, C-H, and -NH) involved in the adsorption of Cd2+ through fourier transform infrared spectroscopy (FTIR). After applying MI to Cd-contaminated soil, it was found that soil pH, conductivity (EC) and soil organic matter (SOM) increased by 0.84 %-2.43 %, 31.6 %-241.48 %, and 8.11 %-24.1 %, respectively, when compared with the control treatments. The content of DTPA-Cd in the soils was significantly (P < 0.05) reduced by 15.48 %-29.68 % in contrast with CK, and the Cd speciation was transformed into a more stable residual fraction. The activities of urease, phosphatase and sucrose were increased by 3.5 %-45.18 %, 57.00 %-134.18 % and 52.51 %-70.52 %, respectively, compared with CK. Therefore, MI could be used as an ecofriendly and sustainable material for bioremediation of Cd-contaminated soils.