Malathion, an extensively used organophosphorus pesticide, poses a high potential risk of toxicity to humans and the environment. Shewanella (S.) oneidensis MR-1 has been proposed as a strain with excellent bioremediation capabilities, capable of efficiently removing a wide range of hard-to-degrade pollutants. However, the physiological and biochemical response of S. oneidensis MR-1 to malathion is unknown. Therefore, this study aimed to examine how S. oneidensis MR-1 responds physiologically and biochemically to malathion while also investigating the biodegradation properties of the pesticide. The results showed that the 7-day degradation rates of S. oneidensis MR-1 were 84.1, 91.6, and 94.0% at malathion concentrations of 10, 20, and 30 mg/L, respectively. As the concentration of malathion increased, superoxide dismutase and catalase activities were inhibited, leading to a significant rise in malondialdehyde content. This outcome can be attributed to the excessive production of reactive oxygen species (ROS) triggered by malathion stress. In addition, ROS production stimulates the secretion of soluble polysaccharides, which alleviates oxidative stress caused by malathion. Malathion-induced oxidative damage further exacerbated the changes in the cellular properties of S. oneidensis MR-1. During the initial stages of degradation, the cell density and total intracellular protein increased significantly with increasing malathion exposure. This can be attributed to the remarkable resistance of S. oneidensis MR-1 to malathion. Based on scanning electron microscopy observations, continuous exposure to contaminants led to a reduction in biomass and protein content, resulting in reduced cell activity and ultimately leading to cell rupture. In addition, this was accompanied by a decrease in Na⁺/K⁺- ATPase and Ca²⁺/Mg²⁺-ATPase levels, suggesting that malathion-mediated oxidative stress interfered with energy metabolism in S. oneidensis MR-1. The findings of this study provide new insights into the environmental risks associated with organophosphorus pesticides, specifically malathion, and their potential for bioremediation. Graphical Abstract

Chromium (Cr) contamination, widely present in the environment, poses a significant threat to both ecology and human health. Microbial remediation technology has become a hot topic in the field of heavy metal remediation due to its advantages, such as environmental protection, low cost, and high efficiency. This paper focused on using various characterization and analysis methods to investigate the bioreduction effect and mechanism of microorganisms on Cr(VI) under various influencing factors. The main contents and conclusions were as follows: Shewanella oneidensis MR-1 was selected as the target strain for studying its reduction of Cr(VI) at different inoculation amounts, temperatures, pH values, time intervals, etc. The results indicated that S. oneidensis MR-1 exhibited an optimal reduction effect on Cr(VI) at pH 7 and a temperature of 35 °C. Additionally, electron shuttles (ESs), including humic acid (HA) and 9,10-antraquinone-2,6-disulfonate (AQDS), were introduced into the degradation system to improve the reduction efficiency of S. oneidensis MR-1. Upon adding goethite further, S. oneidensis MR-1 significantly enhanced its reducing ability by converting Fe(III) minerals to Fe(II) and reducing Cr(VI) to Cr(III) during electron transfer.

Background: Ofloxacin (OFL) is stable and difficult to degrade. It has been detected in water, soil, and plants throughout the world. This study domesticated OFL-contaminated livestock manure soil with simplified carbon sources to identify flora capable of effectively degrading OFL. The changes in the structural composition and diversity of the microbial community and the functional abundance of the soil flora were analyzed by metagenome sequencing technology. The Biolog-ECO microplate method was used to study the utilization of 31 different carbon sources by selected bacteria and to identify the best co-metabolized carbon source for degradation. Results: Amino acid carbon sources were more likely to cause significant changes in community structures with increasing OFL concentrations during the acclimation stage. The abundance of Sphingobacterium decreased from 69.23% to 9.84%, while Alcaligenes increased from 0.27% to 62.79%, and Stenotrophomonas increased from 11.63% to 33.33%, becoming the dominant genus. The results suggested that Stenotrophomonas and Alcaligenes were potential candidate bacteria for the degradation of quinolone antibiotics, such as OFL. Compared with the first stage of acclimation, there was an 87% increase (the concentration was 30 mg·L⁻¹) in the OFL degradation rate by functional flora obtained by gradient acclimation, and the functional abundance of the microbial community also increased and stabilized with the depth of the domestication process. The most significant changes in membrane transport were observed in the functional abundance of the microbial community, and it was found that itaconic acid, Tween 80, and L-aspartic acid could increase the biomass of the microbial community under OFL stress. Conclusion: Significant changes in the bacterial composition and functional abundance of the microbial community resulted from the addition of amino acid carbon sources, together with the OFL concentration. Functional flora resulting from domestication were better able to degrade OFL. The addition of a co-metabolic carbon source significantly enhanced the biomass of the functional flora. In this study, co-metabolism was performed by adding specific carbon sources, thus achieving metabolic diversity of functional flora and ultimately efficient biodegradation of OFL. This was an important discovery in the field of microbial remediation of environmental contamination.

A complete series of the calcite–otavite solid solutions [(Ca_1−xCd_x)CO₃] were prepared, and their dissolution processes lasting nine months were experimentally investigated. For the dissolution in the N₂-degassed water, the Ca concentrations of the aqueous phases increased up to the steady states after 5040 h of dissolution, and the Cd concentrations of the aqueous phases increased up to the highest values and then decreased gradually to the steady states of 0.017–6.476 μmol/L after 5040 h of dissolution. For the dissolution in the CO₂-saturated water, the Ca and Cd concentrations of the aqueous phases increased up to the peak values and then decreased gradually to the steady states of 0.94–0.46 mmol/L and 0.046–9.643 μmol/L after 5040 h of dissolution, respectively. For the dissolution in the N₂-degassed water at 25 °C, the mean solubility products (log K_sp) and the Gibbs free energies of formation (ΔG_f^θ) were estimated to be −8.45–−8.42 and −1129.65–−1129.48 kJ/mol for calcite [CaCO₃] and −11.62–−11.79 and −671.81–−672.78 kJ/mol for otavite [CdCO₃], respectively. Generally, the log K_sp values decreased non-linearly, and the ΔG_f^θ values increased linearly with the increasing Cd/(Ca+Cd) mole ratio (X_Cd) of the (Ca_1−xCd_x)CO₃ solid solutions. In the Lippmann diagrams constructed for the sub-regular (Ca_1−xCd_x)CO₃ solid solutions with the estimated Guggenheim coefficients a₀ = −0.84 and a₁ = −3.80 for the dissolution in the N₂-degassed water or a₀ = −1.12 and a₁ = −3.83 for the dissolution in the CO₂-saturated water, the (Ca_1−xCd_x)CO₃ solid solutions dissolved incongruently, moved progressively up to the quasi-equilibrium curves for otavite and then along the quasi-equilibrium curve from right to left, approached the solutus curve and finally reached the minimum stoichiometric saturation curve for calcite. The considerably Cd-poor aqueous phases were finally in equilibrium with the CdCO₃-rich solid phases.

Arsenic is highly toxic and carcinogenic. The aim of the present work is to develop a good remediation technique for arsenic-contaminated soils. Here, a novel remediation technique by coupling electrokinetics (EK) with the permeable reactive barriers (PRB) of Fe/Mn/C-LDH composite was applied for the remediation of arsenic-contaminated soils. The influences of electric field strength, PRB position, moisture content and PRB filler type on the removal rate of arsenic from the contaminated soils were studied. The Fe/Mn/C-LDH filler synthesized by using bamboo as a template retained the porous characteristics of the original bamboo, and the mass percentage of Fe and Mn elements was 37.85%. The setting of PRB of Fe/Mn/C-LDH placed in the middle was a feasible option, with the maximum and average soil leaching toxicity removal rates of 95.71% and 88.03%, respectively. When the electric field strength was 2 V/cm, both the arsenic removal rate and economic aspects were optimal. The maximum and average soil leaching toxicity removal rates were similar to 98.40% and 84.49% of 3 V/cm, respectively. Besides, the soil moisture content had negligible effect on the removal of arsenic but slight effect on leaching toxicity. The best leaching toxicity removal rate was achieved when the soil moisture content was 35%, neither higher nor lower moisture content in the range of 25–45% was conducive to the improvement of leaching toxicity removal rate. The results showed that the EK-PRB technique could effectively remove arsenic from the contaminated soils. Characterizations of Fe/Mn/C-LDH indicated that the electrostatic adsorption, ion exchange, and surface functional group complexation were the primary ways to remove arsenic.

Arsenic (As(V)), a highly toxic metalloid, is known to contaminate wastewater and groundwater and is difficult to degrade in nature. However, the development of highly efficient adsorbents, at a low cost for use in practical applications, remains highly challenging. Thus, to investigate the As(V) adsorption mechanism, a novel porous α-Fe₂O₃/Fe₃O₄/C composite (PC-Fe/C-B) was prepared, using bamboo side shoots as a bio-template, and the breakthrough performance of the PC-Fe/C-B composite-packed fixed-bed column in As(V) removal was evaluated, using simulated wastewater. The PC-Fe/C-B material accurately retained the hierarchical porous microstructure of the bamboo bio-templates, and the results demonstrated the great potential of PC-Fe/C-B composite, as an effective adsorbent for removing As(V) from wastewater, under the optimal experimental conditions of: influent flow 5.136 mL/min, pH 3, As(V) concentration 20 mg/L, adsorbent particle size < 0.149 mm, adsorption temperature 35 °C, PC-Fe/C-B dose 0.5 g, and breakthrough time 50 min (184 BV), with q_e,exp of 21.0 mg/g in the fixed-bed-column system. The CD-MUSIC model was effectively coupled with the transport model, using PHREEQC software, to simulate the reactive transportation of As(V) in the fixed-bed column and to predict the breakthrough curve for column adsorption.