Microbial induced phosphate precipitation accelerate lead mineralization to alleviate nucleotide metabolism inhibition and alter Penicillium oxalicum's adaptive cellular machinery

A cooperation mechanism between Bacillus thuringiensis and Citrobacter freundii that enhances cadmium biomineralization

The viability and tolerance of individual ureolytic bacteria are a bottleneck in the remediation of cadmium (Cd) by microbially induced carbonate precipitation (MICP) technology. To solve this issue, strains of Bacillus thuringiensis (B. thuringiensis, BT) and Citrobacter freundii (C. freundii, CF) were isolated from soil and studied for their growth characteristics and metabolism. A cooperation system (BT+CF, 1:1, v/v) was constructed and exposed to 20 mg/kg Cd2 + for 7 days, compared with individual bacteria. The synergistic mechanism of strains that immobilize Cd2+ was explored using characterization techniques. Results showed that the main metabolic pathways leading to urea up-regulation were pyrimidine metabolism, urea cycle, and lysine degradation by metabolomic analysis. The cooperation system can effectively remove Cd2+ with an efficiency of 97.68 %, which is higher than BT (66.66 %) and CF (88.61 %). The SEM-EDS, TEM, and XPS results revealed that the calcium carbonate polycrystals (vaterite and calcite) were formed during the MICP process, and the XRD and FTIR confirmed that the BT+CF produces more stable carbonate crystals. The BT+CF cooperation system was efficient at immobilizing Cd2+ by synergizing the molecular mechanisms of ureolytic bacteria. These results provide a novel perspective for the application of MICP.

Back to chromite as a mineralogical strategy for long-term chromium pollution control

Re-oxidation of Cr(III) in treated Cr-contaminated sites poses a considerable source of Cr(VI) pollution, necessitating stable treatment solutions for long-term control. This study explores the immobilization of Cr(VI) into chromite, the most stable and weathering-resistant Cr-bearing mineral, under ambient conditions. Batch experiments demonstrate chromite formation at pH above 7 and Fe(III)/Cr(III) ratios exceeding 1, with Fe(III) occupying all tetrahedral sites, essential for stability. A theoretical model is developed to evaluate the effects of pH and Fe(III)/Cr(III) ratios on chromite crystallinity, resulting in AI4Min-Cr, a publicly accessible platform offering real-time intelligent remediation strategies. To tackle the complexities of non-point source Cr pollution, we employ microbial methods to regulate on-site Eh and pH, optimizing chromite precipitation. Long-term stability tests confirm that chromite remained stable for over 180 days, with potential for magnetic separation recovery. This study presents a mineralogical strategy to address re-oxidation and Cr resource recovery in Cr-contaminated water and soil.

Dual application of lotus stem in fabricating a bioreactor for the remediation of nitrate, plumbum, and carbamazepine in industrial wastewater

Addressing the treatment of complex industrial wastewater continues to be a substantial challenge within the realm of water treatment. A biofilm reactor was engineered, integrating lotus stem biochar, lotus stem biological filler, and the ZW5 strain for enhanced wastewater treatment. The removal efficiencies of nitrate (NO3--N), calcium (Ca2+), chemical oxygen demand (COD), phosphorus (PO43--P), plumbum (Pb2+), and carbamazepine (CBZ) were 98.46, 81.08, 91.79, 96.63, 97.75, and 99.26% when HRT was 3 h, pH was 7.0, Pb2+, CBZ, and influent salinity contents were 15.0, 3.0, and 1500 mg L-1. The reactor effectively fixed the microorganisms and provided a good microenvironment and niche, which was conducive to the adsorption of Pb2+ and CBZ by microorganisms and biominerals. Furthermore, the modified biochar in the reactor filler facilitated microbial metabolism and enabled indirect electron transfer. Microorganisms altered their dominant community structure in response to Pb2+ and CBZ exposure. Microorganisms maintained efficient activity through synergy and direct electron transfer through nanowires. The reactor serves as a model for pollutant removal from complex industrial wastewater, leveraging the multifaceted use of lotus stems and microbial-induced calcium precipitation.

Immobilizing lead in aqueous solution and loess soil using microbially induced carbonate/phosphate precipitation (MICP/MIPP) under harsh pH environments

The bioaccumulation of heavy metals due to metallurgical and smelting activities threatens human health. Although microbial-induced carbonate/phosphate precipitation (MICP/MIPP) technology has been applied to heavy metal remediation, the relative merits of MICP and MIPP, especially under extreme pH environments, have not yet been documented. In this study, Sporosarcina pasteurii (SP)-based MICP and Bacillus megaterium (BM)-based MIPP were applied to immobilize lead (Pb) in aqueous solution and loess soil. The results showed that the BM retained a strong phosphorolysis ability when under strongly acidic conditions, while the ureolysis ability of SP approached zero. Furthermore, the bioprecipitates obtained under BM-based MIPP had a denser appearance, presumably due to the enrichment of calcite and apatite crystals. The results also showed that Pb immobilization was achieved through bacterial adsorption, the chelate function of sodium glycerophosphate (SGP), large organic matter complexation, and biomineralization through the MICP/MIPP mechanism. Under SP-based MICP, SP and large organic matter immobilized Pb2+ at rates of 17.6 % and 31.7 %, respectively, while under BM-based MIPP, BM, organic matter, and SGP immobilized Pb2+ at rates of 21.5 %, 23.4 %, and 48.5 % respectively. The MICP and MIPP mechanisms dominated Pb immobilization at rates of 78.6 % and 99.6 %, respectively.

Comparative transcriptomic and metabolomic analyses provide insights into the responses to high temperature stress in Alfalfa (Medicago sativa L.)

High temperature stress is one of the most severe forms of abiotic stress in alfalfa. With the intensification of climate change, the frequency of high temperature stress will further increase in the future, which will bring challenges to the growth and development of alfalfa. Therefore, untargeted metabolomic and RNA-Seq profiling were implemented to unravel the possible alteration in alfalfa seedlings subjected to different temperature stress (25 ℃, 30 ℃, 35 ℃, 40 ℃) in this study. Results revealed that High temperature stress significantly altered some pivotal transcripts and metabolites. The number of differentially expressed genes (DEGs) markedly up and down-regulated was 1876 and 1524 in T30_vs_CK, 2, 815 and 2667 in T35_vs_CK, and 2115 and 2, 226 in T40_vs_CK, respectively. The number for significantly up-regulated and down-regulated differential metabolites was 173 and 73 in T30_vs_CK, 188 and 57 in T35_vs_CK, and 220 and 66 in T40_vs_CK, respectively. It is worth noting that metabolomics and transcriptomics co-analysis characterized enriched in plant hormone signal transduction (ko04705), glyoxylate and dicarboxylate metabolism (ko00630), from which some differentially expressed genes and differential metabolites participated. In particular, the content of hormone changed significantly under T40 stress, suggesting that maintaining normal hormone synthesis and metabolism may be an important way to improve the HTS tolerance of alfalfa. The qRT-PCR further showed that the expression pattern was similar to the expression abundance in the transcriptome. This study provides a practical and in-depth perspective from transcriptomics and metabolomics in investigating the effects conferred by temperature on plant growth and development, which provided the theoretical basis for breeding heat-resistant alfalfa.

Immobilization of Pb(II) by Bacillus megaterium-based microbial-induced phosphate precipitation (MIPP) considering bacterial phosphorolysis ability and Ca-mediated alleviation of lead toxicity

Inappropriate handling of lead (Pb)-containing wastewater that is produced as a result of smelting activities threatens the surrounding environment and human health. The microbial-induced phosphate precipitation (MIPP) technology was applied to immobilize Pb2+ in an aqueous solution considering bacterial phosphorolysis ability and Ca-mediated alleviation of lead toxicity. Pb immobilization was accompanied by sample characterization in order to explore the inherent mechanism that affected the immobilization efficiency. Results showed that Ca2+ use elevated the immobilization efficiency through the prevention of bacterial physisorption and chemisorption, an enhancement to the phosphatase activity and the degree of SGP hydrolysis, and the provision of nucleation sites for Pb2+ to attach. The formation of the Pb-GP complex helped the bacteria to maintain its activity at the commencement of catalyzing SGP hydrolysis. The nucleated minerals that were precipitated in a columnar shape through a directional stacking manner under MIPP featured higher chemical stability compared to non-nucleated minerals. As a result, there were three pathways, namely, bacterial physisorption, bacterial chemisorption, and substrate chelation, applied for Pb immobilization. The immobilization efficiency of 99.6% is achieved by precipitating bioprecipitates including Pb5(PO4)3Cl, Pb10(PO4)6Cl2, and Ca2Pb3(PO4)3Cl. The findings accentuate the potential of applying the MIPP technology to Pb-containing wastewater remediation.

β-tricalcium phosphate enhanced biomineralization of Cd2+ and Pb2+ by Sporosarcina ureilytica HJ1 and Sporosarcina pasteurii HJ2

Microbiologically induced CaCO3 precipitation (MICP) has been proposed as a potential bioremediation method to immobilize contaminating metals. In this study, carbonate mineralizing bacteria HJ1 and HJ2, isolated from heavy metal contaminated soil, was employed for Cd2+ and Pb2+ immobilization with or without β-tricalcium phosphate addition. Compared with the only treatments amended with strains, the combined application of β-tricalcium phosphate and HJ1 improved the immobilization rates of Cd and Pb by 1.49 and 1.70 times at 24 h, and the combined application of β-tricalcium phosphate and HJ2 increased the immobilization rates of Cd and Pb by 1.25 and 1.79 times. The characterization of biomineralization products revealed that Cd2+ and Pb2+ primarily immobilized from the liquid phase as CdCO3 and PbCO3, and the addition of β-tricalcium phosphate facilitated the formation of Ca4.03Cd0.97(PO4)3(OH) and Pb3(PO4)2. Also, the calcium source was related to the speciation of carbonate precipitation and improved the Cd and Pb remediation efficiency. This research demonstrated the feasibility and effectiveness of MICP combined with β-tricalcium phosphate in immobilization of Cd and Pb, which will provide a fundamental basis for future applications of MICP to mitigate soil heavy metal pollutions.

Enhancement of nitrogen on core taxa recruitment by Penicillium oxalicum stimulated microbially-driven soil formation in bauxite residue

Microbially-driven soil formation process is an emerging technology for the ecological rehabilitation of alkaline tailings. However, the dominant microorganisms and their specific roles in soil formation processes remain unknown. Herein, a 1-year field-scale experiment was applied to demonstrate the effect of nitrogen input on the structure and function of the microbiome in alkaline bauxite residue. Results showed that the contents of nutrient components were increased with Penicillium oxalicum (P. oxalicum) incorporation, as indicated by the increasing of carbon and nitrogen mineralization and enzyme metabolic efficiency. Specifically, the increasing enzyme metabolic efficiency was associated with nitrogen input, which shaped the microbial nutrient acquisition strategy. Subsequently, we evidenced that P. oxalicum played a significant role in shaping the assemblages of core bacterial taxa and influencing ecological functioning through intra- and cross-kingdom network analysis. Furthermore, a recruitment experiment indicated that nitrogen enhanced the enrichment of core microbiota (Nitrosomonas, Bacillus, Pseudomonas, and Saccharomyces) and may provide benefits to fungal community bio-diversity and microbial network stability. Collectively, these results demonstrated nitrogen-based coexistence patterns among P. oxalicum and microbiome and revealed P. oxalicum-mediated nutrient dynamics and ecophysiological adaptations in alkaline microhabitats. It will aid in promoting soil formation and ecological rehabilitation of bauxite residue. ENVIRONMENT IMPLICATION: Bauxite residue is a highly alkaline solid waste generated during the Bayer process for producing alumina. Attempting to transform bauxite residue into a stable soil-like substrate using low-cost microbial resources is a highly promising engineering. However, the dominant microorganisms and their specific roles in soil formation processes remain unknown. In this study, we evidenced the nitrogen-based coexistence patterns among Penicillium oxalicum and microbiome and revealed Penicillium oxalicum-mediated nutrient dynamics and ecophysiological adaptations in alkaline microhabitats. This study can improve the understanding of core microbes' assemblies that affect the microbiome physiological traits in soil formation processes.

Application of phosphogypsum and phosphate-solubilizing fungi to Pb remediation: From simulation to in vivo incubation

Phosphogypsum (PG) is the produced solid waste during phosphorus (P) extraction from phosphate rocks. PG is featured by its abundant PO43- and SO42-. This study investigated the utilization of PG as a material for lead (Pb) remediation, with the assistance of functional fungus. Aspergillus niger (A. niger) is a typical phosphate-solubilizing fungi (PSF), which has high ability to secret organic acids. Oxalic acid is its major secreted organic acid, which is often applied to enhance the P release from phosphate minerals. In this study, synthetic oxalic acid increased the immobilization rate of Pb2+ up to >99 % with the addition of PG. Then, it was observed that biogenic oxalic acid from A. niger can achieve comparable remediation effects. This was due to that PG could provide sufficient P for fungal growth, which allowed sustainable remediation. Subsequently, oxalic acid secreted by A. niger significantly increased the release of active P from PG, and then induced the formation of PPb minerals. In addition, other metabolites of A. niger (such as tyrosine-like substance) can also be complexed with Pb2+. Simultaneously, A. niger did not induce evidently elevation water-soluble fluorine (F) as PG contained abundant Ca2+. Moreover, this study elucidated that oversupply of PG promoted the formation of anglesite (Ksp = 1.6 × 10-8, relatively unstable), whereas the formation of lead oxalate (Ksp = 4.8 × 10-10, relatively stable) was reduced. This study hence shed a bright light on the sustainable utilization of PG for fungus-assisted remediation of heavy metals.

Penicillium oxalicum induced phosphate precipitation enhanced cadmium (Cd) immobilization by simultaneously accelerating Cd biosorption and biomineralization

Soil cadmium (Cd) is immobilized by the progressing biomineralization process as microbial induced phosphate precipitation (MIPP), which is regulated by phosphate (P) solubilizing microorganisms and P sources. However, little attention has been paid to the implications of Cd biosorption during MIPP. In this study, the newly isolated Penicillium oxalicum could immobilize 5.4-12.6 % of Cd2+, while the presence of hydroxyapatite (HAP) considerably enhanced Cd2+ immobilization in P. oxalicum and reached over 99 % Cd2+ immobilization efficiency within 7 days. Compared to P. oxalicum mono inoculation, MIPP dramatically boosted Cd biosorption and biomineralization efficiency by 71 % and 16 % after 96 h cultivation, respectively. P. oxalicum preferred to absorbing Cd2+ and reaching maximum Cd2+ biosorption efficiency of 87.8 % in the presence of HAP. More surface groups in P. oxalicum and HAP mineral involved adsorption which resulted in the formation of Cd-apatite [Ca8Cd2(PO4)6(OH)2] via ion exchange. Intracellular S2-, secreted organic acids and soluble P via HAP solubilization complexed with Cd2+, progressively mineralized into Cd5(PO4)3OH, Cd(H2PO4)2, C4H6CdO4 and CdS. These results suggested that Cd2+ immobilization was enhanced simultaneously by the accelerated biosorption and biomineralization during P. oxalicum induced P precipitation. Our findings revealed new mechanisms of Cd immobilization in MIPP process and offered clues for remediation practices at metal contaminated sites.

Endophytic Fungus Talaromyces sp. MR1 Promotes the Growth and Cadmium Uptake of Arabidopsis thaliana L. Under Cadmium Stress

Endophytes play essential roles in plant growth under metal(loid)s stress. An endophytic fungus strain MR1 was isolated from the roots of Miscanthus floridulus collected from a lead-zinc mining area (Huayuan, China), which could produce indole-3-acetic acid and have Cadmium (Cd) tolerance. Further 18S rRNA sequencing analysis showed that it was highly similar (99.83%) to Talaromyces pinophilus. In pot experiments, we explored the effects of strain MR1 on the growth and Cd uptake of a wide-type Arabidopsis thaliana under low (LC) and high (HC) Cd concentrations. The results showed that MR1 effectively increased the dry weight of aboveground and underground tissues by 25.95-107.21% in both LC and HC groups. Due to MR1 inoculation, the Cd content in the underground tissues was significantly (p < 0.05) decreased by 39.28% under low Cd concentration, while it was significantly (p < 0.05) increased by 28.28% under high Cd concentration. Besides, MR1 inoculations significantly (p < 0.05) increased the total content of removed Cd (17.080 μg) and BCF (0.064) by 129.77% and 153.95% under high Cd concentration. Therefore, we speculated that MR1 might be selected as the effective microbial agent to increase crop yield and control Cd content in the crop in light Cd-contaminated soil. Besides, MR1 could potentially enhance the phytoremediation efficiency of extremely Cd-contaminated soil.

Hierarchical stringent response behaviors of activated sludge system to stressed conditions

The stringent response of activated sludge systems to either stressed or harmful environments is important for the stable operation of activated sludge, which is examined by taking copper ion (Cu²⁺) as a stress model in this study. When weak stress was employed (Cu²⁺ ≤ 2.5 mg/L), the N-acyl-homoserine lactones (AHLs) of C6-, C8-, and C10-HSL increased by 30 %, 13 %, and 127 %, respectively, while the redox sensor green (RSG) intensity decreased by 28 %. Encountering the increased stress (2.5 mg/L < Cu²⁺ ≤ 5 mg/L), bacteria concentration in the supernatant increased by 87 %. However, the respiration rates of autotrophic and heterotrophic bacteria (SOUR_a and SOUR_h) and adenosine triphosphate decreased by 52 %, 18 %, and 27 %, respectively, and the flocs disintegrated with a diameter decreasing from 57 to 51 μm. When the stress became more serious (Cu²⁺ > 5 mg/L), the respiration rates continued to decline, but the quasi-endogenous respiration ratio (R_q/t) increased from 31 % to 47 %. Negligible changes occurred in the endogenous respiration rate (SOUR_e), adenosine diphosphate, and adenosine monophosphate. Based on these results, a hierarchical stringent response model of the activated sludge system to stressed conditions was proposed, and these responses were evaluated by respirogram. The initial response to weak stress was related to the most sensitive signals of quorum sensing and RSG intensity, well described by the quasi-endogenous respiration rate. The adaptive response to increased stress was the proactive migrations of low- and high-nucleic-acid bacteria to the supernatant, causing the looseness and even disintegration of sludge flocs, well described by SOUR_a, SOUR_h, and R_q/t. The lethal response to lethal stress was related to endogenous metabolic processes, well described by SOUR_e. This work provides new insights into understanding the stringent response of activated sludge systems to some stressed conditions. It helps to regulate the stability of activated sludge systems with respirogram technology.