Transport and retention of Shewanella oneidensis strain MR1 in water-saturated porous media with different grain-surface properties

Strategy and mechanisms of sulfamethoxazole removal from aqueous systems by single and combined Shewanella oneidensis MR-1 and nanoscale zero-valent iron-enriched biochar

Sulfamethoxazole (SMX, a sulfonamide antibiotic) is ubiquitously present in various aqueous systems, which can accelerate the spread of antibiotic resistance genes, induce genetic mutations, and even disrupt the ecological equilibrium. Considering the potential eco-environmental risk of SMX, this study explored an effective technology using Shewanella oneidensis MR-1 (MR-1) and nanoscale zero-valent iron-enriched biochar (nZVI-HBC) to remove SMX from aqueous systems with different pollution levels (1-30 mg·L^-1). SMX removal by nZVI-HBC and nZVI-HBC + MR-1 (55-100 %) under optimal conditions (iron/HBC ratio of 1:5, 4 g·L^-1 nZVI-HBC, and 10 % v/v MR-1) was more effective than its removal by MR-1 and biochar (HBC) (8-35 %). This was due to the catalytic degradation of SMX in the nZVI-HBC and nZVI-HBC + MR-1 reaction systems because of accelerated electron transfer during oxidation of nZVI and reduction of Fe(III) to Fe(II). When SMX concentration was lower than 10 mg·L^-1, nZVI-HBC + MR-1 effectively removed SMX (removal rate of approximately 100 %) when compared to nZVI-HBC (removal rate of 56-79 %). In addition to oxidation degradation of SMX by nZVI in the nZVI-HBC + MR-1 reaction system, MR-1-driven dissimilatory iron reduction accelerated electron transfer to SMX, thereby enhancing reductive degradation of SMX. However, a considerable decline in SMX removal from the nZVI-HBC + MR-1 system (42 %) was observed when SMX concentrations ranged 15-30 mg·L^-1, which was due to the toxicity of accumulated degradation products of SMX. A high interaction probability between SMX and nZVI-HBC promoted the catalytic degradation of SMX in the nZVI-HBC reaction system. The results of this study provide promising strategies and insights for enhancing antibiotic removal from aqueous systems with different pollution levels.

Mechanistic insights into aggregation process of graphene oxide and bacterial cells in microbial reduction of ferrihydrite

Microbial reduction of ferrihydrite is prevalent in natural environments and plays an important role in reductive dissolution of Fe(III) minerals. With consistent release of anthropogenic graphene oxide (GO) into water bodies, new changes in the Fe(III)-reducing microorganisms/ferrihydrite binary system demand attention. Herein, we focused on the interaction of GO and bacterial cells in view of colloidal stability and interfacial forces, and on the consequences for microbial ferrihydrite reduction. The results showed that the addition of GO decreased the bioreduction efficiency of ferrihydrite down to 1/15 of the control. Meanwhile, the GO nanosheets were found not depositing on ferrihydrite but spontaneously aggregating with Shewanella spp., the representative dissimilatory Fe(III) reduction bacterial species. Using the extended Derjaguin-Landau-Verwey-Overbeek (XDLVO) theory and atomic force microscopy (AFM), the aggregation process can be interpreted in three steps according to the interaction energy calculation, namely, colloidal instability, reversible aggregation and irreversible aggregation. The motility of living cells seems the reason inducing the colloidal instability between GO and bacteria. While, the aggregation remains reversible even the secondary minimum achieved at the separation distance of 8.74-9.24 nm from XDLVO. When the separation distance <5.74-6.01 nm, the adhesion work predominates and causes irreversible aggregation, validated by AFM. Additionally, the probable ecological risks raised by this aggregation behavior for the imbalance of iron biogeochemical cycle were demonstrated.

A unified parameter model based on machine learning for describing microbial transport in porous media

The transport and retention of microorganisms are typically described using attachment/detachment and straining/liberation models. However, the parameters in the models varied significantly, posing a significant challenge to describe microbial transport under different environmental conditions. A neural network (ANN) model was developed in this study to link the parameters in the model with the factors influencing microbial transport including the properties of microorganisms such as size and surface potentials, and the properties of porous media such as grain size and porosity, and flow conditions. Exhaustive search of literature renders 420 sets of experimental data of microbial transport, which were fitted using the microbial transport model to obtain model parameters. The model parameters, together with the factors influencing microbial transport, were then used to train an ANN model to search for their relationship. An ANN-based parameter relationship was derived and was then used to simulate microbial transport. The simulated results using the relationship roughly matched with the experimental data under different environmental conditions, indicating that a unified relationship was established between the parameters of the microbial transport model and the factors influencing microbial transport, and that microbial transport can be described using the microbial transport model with the ANN-based unified relationship for model parameters.

Transport of silver nanoparticles coated with polyvinylpyrrolidone of various molecular sizes in porous media: Interplay of polymeric coatings and chemically heterogeneous surfaces

Silver nanoparticles (AgNPs) are usually capped with stabilizing agents to protect their activities and improve stability. Polyvinylpyrrolidone (PVP) is one of the most used capping agents of AgNPs, and may affect the transport of AgNPs in porous media. The transport and retention of AgNPs capped with PVPs of different molecular weights (PVP10-AgNP, PVP40-AgNP and PVP360-AgNP) in uncoated, and humic acid (HA)-, kaolinite (KL)- and ferrihydrite (FH)-coated sand porous media were investigated. Among the three AgNPs, PVP360-AgNP exhibited the highest mobility and eluted from all types of porous media. This is because PVPs of higher molecular weight provided stronger steric effect and electrostatic repulsive forces among PVP-AgNPs, inducing stronger blocking and shadow effects. The transport of the PVP-AgNPs increased in the HA-Sand columns, while decreased in the KL- and FH-Sand columns, especially for PVP10-AgNP and PVP40-AgNP. The simulation results using one-site kinetic model indicated that HA-Sand reduced the maximum retention capacity (Smax), while KL- and FH-Sand increased the Smax as well as the first-order attachment rate coefficients (katt), particularly at high ionic strength. The results shed light on the interplay of the capping agents of AgNPs and the surface heterogeneity on the transport of AgNPs in porous media.

Effect of Shewanella oneidensis MR-1 on U(VI) sequestration by montmorillonite

Bacteria may change the physicochemical properties of montmorillonite and further effect the disposal of high-level radioactive waste. Therefore, we explored the influence of Shewanella oneidensis MR-1 on the elimination of representative radionuclide U(VI) by montmorillonite (MMT). The batch experiments showed that MR-1 significantly enhanced the removal efficiency of U(VI), the adsorption capacity of MMT improved from 8.4 to 16.1 mg/g after addition of MR-1, and the adsorption type changed from Langmuir to Freundlich. FTIR and XPS analysis revealed that hydroxyl, phosphate, carbonyl and amine in MMT + MR-1 were primary actors in the elimination of U(VI). The U 4f high-resolution XPS spectrum of MMT + MR-1 showed U(VI) and U(IV) peaks at the same time, indicating that the adsorption process was accompanied by the reduction reaction, which may be due to the extracellular respiration of MR-1. These investigations are significant to insight the potential significance of microbial processes for the transport and elimination of U(VI) in repositories, which in return will contribute to their safe disposal.

A novel real-time TMAO detection method based on microbial electrochemical technology

Trimethylamine N-oxide (TMAO) is considered to be a novel biomarker of cardiovascular diseases. However, the traditional TMAO detection method has failed to meet the requirements of real-time and point-of-care tests. Herein, a novel TMAO detection method based on microbial electrochemical technology is established, which realizes the direct conversion of TMAO concentration into electrical signals. Attached Shewanella loihica PV-4 was first proven to be capable of simultaneous inward extracellular electron transfer and TMAO reduction. The TMAO detection method showed a wide linear range of 0 to 250 μM, a high sensitivity of 23.92 μA/mM, and a low limit of detection of 5.96 μM. In addition, the TMAO detection process was accomplished within 600 s, with an acceptable accuracy of 90% in the real serum, showing high feasibility in clinical applications.