Characterization of the cell surface and cell wall chemistry of drinking water bacteria by combining XPS, FTIR spectroscopy, modeling, and potentiometric titrations

A novel glycosyltransferase from Bacillus subtilis achieves zearalenone detoxification by diglycosylation modification

Zearalenone (ZEN), a nonsteroidal estrogenic mycotoxin produced by Fusarium spp., contaminates cereals and threatens human and animal health by inducing hepatotoxicity, immunotoxicity, and genotoxicity. In this study, a new Bacillus subtilis strain, YQ-1, with a strong ability to detoxify ZEN, was isolated from soil samples and characterized. YQ-1 was confirmed to degrade more than 46.26% of 20 μg mL-1 ZEN in Luria-Bertani broth and 98.36% in fermentation broth within 16 h at 37 °C; one of the two resulting products was ZEN-diglucoside. Under optimal reaction conditions (50 °C and pH 5.0-9.0), the reaction mixture generated by YQ-1 catalyzing ZEN significantly reduced the promoting effect of ZEN on MCF-7 cell proliferation, effectively eliminating the estrogenic toxicity of ZEN. In addition, a new glycosyltransferase gene (yqgt) from B. subtilis YQ-1 was cloned with 98% similarity to Bs-YjiC from B. subtilis 168 and over-expressed in E. coli BL21 (DE3). ZEN glycosylation activity converted 25.63% of ZEN (20 μg mL-1) to ZEN-diG after 48 h of reaction at 37 °C. The characterization of ZEN degradation by B. subtilis YQ-1 and the expression of YQGT provide a theoretical basis for analyzing the mechanism by which Bacillus spp. degrades ZEN.

Constructing Two-Dimensional (2D) Heterostructure Channels with Engineered Biomembrane and Graphene for Precise Scandium Sieving

The special properties of rare earth elements (REE) have effectively broadened their application fields. How to accurately recognize and efficiently separate target rare earth ions with similar radii and chemical properties remains a formidable challenge. Here, precise two-dimensional (2D) heterogeneous channels are constructed using engineered E. coli membranes between graphene oxide (GO) layers. The difference in binding ability and corresponding conformational change between Lanmodulin (LanM) and rare earth ions in the heterogeneous channel allows for precisely recognizing and sieving of scandium ions (Sc3+). The engineered E. coli membranes not only can protect the integrity of structure and functionality of LanM, the rich lipids and sugars, but also help the Escherichia coli (E. coli) membranes closely tile on the GO nanosheets through interaction, preventing swelling and controlling interlayer spacing accurately down to the sub-nanometer. Apparently, the 2D heterogeneous channels showcase excellent selectivity for trivalent ions (SFFe /Sc≈3), especially for Sc3+ ions in REE with high selectivity (SFCe/Sc≈167, SFLa/Sc≈103). The long-term stability and tensile strain tests verify the membrane's outstanding stability. Thus, this simple, efficient, and cost-effective work provides a suggestion for constructing 2D interlayer heterogeneous channels for precise sieving, and this valuable strategy is proposed for the efficient extraction of Sc.

Metallic nanoparticle actions on the outer layer structure and properties of Bacillus cereus and Staphylococcus epidermidis

Although the antimicrobial activity of nanoparticles (NPs) penetrating inside the cell is widely recognised, the toxicity of large NPs (>10 nm) that cannot be translocated across bacterial membranes remains unclear. Therefore, this study was performed to elucidate the direct effects of Ag-NPs, Cu-NPs, ZnO-NPs and TiO2-NPs on relative membrane potential, permeability, hydrophobicity, structural changes within chemical compounds at the molecular level and the distribution of NPs on the surfaces of the bacteria Bacillus cereus and Staphylococcus epidermidis. Overall analysis of the results indicated the different impacts of individual NPs on the measured parameters in both strains depending on their type and concentration. B. cereus proved to be more resistant to the action of NPs than S. epidermidis. Generally, Cu-NPs showed the most substantial toxic effect on both strains; however, Ag-NPs exhibited negligible toxicity. All NPs had a strong affinity for cell surfaces and showed strain-dependent characteristic dispersion. ATR-FTIR analysis explained the distinctive interactions of NPs with bacterial functional groups, leading to macromolecular structural modifications. The results presented provide new and solid evidence for the current understanding of the interactions of metallic NPs with bacterial membranes.

Spectroscopic and Microscopic Characterization of Microbial Biofouling on Aircraft Fuel Tanks

Avoiding microbial contamination and biofilm formation on the surfaces of aircraft fuel tanks is a major challenge in the aviation industry. The inevitable presence of water in fuel systems and nutrients provided by the fuel makes an ideal environment for bacteria, fungi, and yeast to grow. Understanding how microbes grow on different fuel tank materials is the first step to control biofilm formation in aviation fuel systems. In this study, biofilms of Pseudomonas putida, a model Gram-negative bacterium previously found in aircraft fuel tanks, were characterized on aluminum 7075-T6 surfaces, which is an alloy used by the aviation industry due to favorable properties including high strength and fatigue resistance. Scanning electron microscopy (SEM) coupled with energy-dispersive X-ray (EDX) showed that extracellular polymeric substances (EPS) produced by P. putida were important components of biofilms with a likely role in biofilm stability and adhesion to the surfaces. EDX analysis showed that the proportion of phosphorus with respect to nitrogen is higher in the EPS than in the bacterial cells. Additionally, different morphologies in biofilm formation were observed in the fuel phase compared to the water phase. Micro-Fourier transform infrared spectroscopy (micro-FTIR) analysis suggested that phosphoryl and carboxyl functional groups are fundamental for the irreversible attachment between the EPS of bacteria and the aluminum surface, by the formation of hydrogen bonds and inner-sphere complexes between the macromolecules and the aluminum surface. Based on the hypothesis that nucleic acids (particularly DNA) are an important component of EPS in P. putida biofilms, the impact of degrading extracellular DNA was tested. Treatment with the enzyme DNase I affected both water and fuel phase biofilms─with the cell structure disrupted in the aqueous phase, but cells remained attached to the aluminum coupons.

Promotion of Humic Acid Transformation by Abiotic and Biotic Fe Redox Cycling in Nontronite

The redox activity of Fe-bearing minerals is coupled with the transformation of organic matter (OM) in redox dynamic environments, but the underlying mechanism remains unclear. In this work, a Fe redox cycling experiment of nontronite (NAu-2), an Fe-rich smectite, was performed via combined abiotic and biotic methods, and the accompanying transformation of humic acid (HA) as a representative OM was investigated. Chemical reduction and subsequent abiotic reoxidation of NAu-2 produced abundant hydroxyl radicals (thereafter termed as ·OH) that effectively transformed the chemical and molecular composition of HA. More importantly, transformed HA served as a more premium electron donor/carbon source to couple with subsequent biological reduction of Fe(III) in reoxidized NAu-2 by Geobacter sulfurreducens, a model Fe-reducing bacterium. Destruction of aromatic structures and formation of carboxylates were mechanisms responsible for transforming HA into an energetically more bioavailable substrate. Relative to unaltered HA, transformed HA increased the extent of the bioreduction by 105%, and Fe(III) reduction was coupled with oxidation and even mineralization of transformed HA, resulting in bleached HA and formation of microbial products and cell debris. ·OH transformation slightly decreased the electron shuttling capacity of HA in bioreduction. Our results provide a mechanistic explanation for rapid OM mineralization driven by Fe redox cycling in redox-fluctuating environments.

Applications of Fourier Transform-Infrared spectroscopy in microbial cell biology and environmental microbiology: advances, challenges, and future perspectives

Microorganisms play pivotal roles in shaping ecosystems and biogeochemical cycles. Their intricate interactions involve complex biochemical processes. Fourier Transform-Infrared (FT-IR) spectroscopy is a powerful tool for monitoring these interactions, revealing microorganism composition and responses to the environment. This review explores the diversity of applications of FT-IR spectroscopy within the field of microbiology, highlighting its specific utility in microbial cell biology and environmental microbiology. It emphasizes key applications such as microbial identification, process monitoring, cell wall analysis, biofilm examination, stress response assessment, and environmental interaction investigation, showcasing the crucial role of FT-IR in advancing our understanding of microbial systems. Furthermore, we address challenges including sample complexity, data interpretation nuances, and the need for integration with complementary techniques. Future prospects for FT-IR in environmental microbiology include a wide range of transformative applications and advancements. These include the development of comprehensive and standardized FT-IR libraries for precise microbial identification, the integration of advanced analytical techniques, the adoption of high-throughput and single-cell analysis, real-time environmental monitoring using portable FT-IR systems and the incorporation of FT-IR data into ecological modeling for predictive insights into microbial responses to environmental changes. These innovative avenues promise to significantly advance our understanding of microorganisms and their complex interactions within various ecosystems.

The evaluation of biotechnological potential of Gp144, the key molecule of natural predator bacteriophage K in Staphylococcus aureus hunting mechanism

Bacteriophages, which selectively infect bacteria, and phage-derived structures are considered promising agents for the diagnosis and treatment of bacterial infections due to the increasing antibiotic resistance. The binding of phages to their specific receptors on host bacteria is highly specific and irreversible, and therefore, the characterization of receptor-binding proteins(RBPs), which are key determinants of phage specificity, is crucial for the development of new diagnostic and therapeutic products. This study highlights the biotechnological potential of Gp144, an RBP located in the tail baseplate of bacteriophage K and responsible for adsorption of phageK to S. aureus. Once it was established that recombinant Gp144 (rGp144)is biocompatible and does not exhibit lytic effects on bacteria, its interaction with the host, the binding efficiency and performance were assessed in vitro using microscopic and serological methods. Results showed that rGp144 has a capture efficiency (CE) of over 87% and the best CE score is %96 which captured 9 CFU mL-1 out of 10 CFU mL-1 bacteria, indicating that very low number of bacteria could be detected. Additionally, it was shown for the first time in the literature that rGp144 binds to both S. aureus and methicillin-resistant S. aureus (MRSA) cells in vitro, while its affinity to different Gram-positive bacteria (E. faecalis and B. cereus) was not observed. The findings suggest that rGp144 can be effectively used for the diagnosis of S. aureus and MRSA, and that the use of RBPs in host-phage interaction can be a novel and effective strategy for imaging and diagnosing the site of infection.

Spatial-temporal clogging development in leachate collection systems of landfills: Insight into chemical and biological clogging characteristics

The clogging of leachate collection systems (LCSs) is a typical challenge for landfills operation. Although clogging occurs in different LCS components, its spatial-temporal distributions remain unclear. This study aimed to systematically investigate the dynamic clogging development in simulated LCSs by monitoring changes in clogging characteristics over time. Results revealed that clogging accumulated in all components of the simulated LCS during a 215-day period, including chemical clogging and bio-clogging. Distinct spatial variations in clogging components were observed along the leachate flow of the simulated LCS, with the geotextile being severely clogged due to bio-clogging (70.1 ± 3.0%-80.0 ± 0.5%). Additionally, chemical clogging mainly occurred at the top (85.4 ± 0.8%-95.0 ± 0.9%) and middle (91.2 ± 0.8%-94.9 ± 1.1%) gravel layers. Nevertheless, the percentage of chemical clogging decreased from 72.0 ± 2.1% (day 42) to 42.5 ± 2.7% (day 215) at the bottom gravel layer. Chemical clogging was the main type in the pipe, accounting for 69.6 ± 0.5% (day 215). In addition, the ratios of bio-clogging to chemical clogging changed over time in all LCS components. The spatial-temporal characteristics of clogging across LCS components can enhance the understanding of clogging mechanisms, facilitate the design optimization of LCSs, and promote the formulation of effective control strategies.

The role of multi-low molecular weight organic acids on phenanthrene biodegradation: Insight from cellular characteristics and proteomics

Polycyclic aromatic hydrocarbons (PAHs) are carcinogenic and ubiquitous pollutants that need to be solved. The low-molecular-weight organic acid (LMWOA) holds the promise to accelerate the capacity of microbes to degrade PAHs. However, the degradation mechanism(s) with multi-LMWOAs has not been understood yet, which is closer to the complex environmental biodegradation in nature. Here, we demonstrated a comprehensive cellular and proteomic response pattern by investigating the relationship between a model PAH degrading strain, B. subtilis ZL09-26, and the mixture LMWOAs (citric acid, glutaric acid, and oxalic acid). As a result, multi-LMWOAs introduced a highly enhanced phenanthrene (PHE) degradation efficiency with up to 3.1-fold improvement at 72 h, which is accompanied by the enhancement of strain growth and activity, but the releasement of membrane damages and oxidative stresses. Moreover, a detailed proteomic analysis revealed that the synergistic perturbation of various metabolic pathways jointly governed the change of cellular behaviors and improved PHE degradation in a network manner. The obtained knowledge provides a foundation for designing the artificial LMWOAs mixtures and guides the rational remediation of contaminated soils using bio-stimulation techniques.

Simultaneous ammonium and water recovery from landfill leachate using an integrated two-stage membrane distillation

Resources recovery from landfill leachate (LFL) has been attracting growing attention instead of merely purifying the wastewater. An integrated two-stage membrane distillation (ITMD) was proposed to simultaneously purify LFL and recover ammonia in this study. The results showed that organics could be always effectively rejected by the ITMD regardless of varying feed pH, with COD removal higher than 99%. With feed pH increased from 8.64 to 12, the ammonia migration (50-100%) and capture (36-75%) in LFL were considerably enhanced, boosting the separated ammonia enrichment to 1.3-1.7 times due to the improved ammonium diffusion. However, the corresponding membrane flux of the first MD stage decreased from 13.7 to 10.5 L/m²·h. Elevating feed pH caused the deprotonation of NOM and its binding with inorganic ions, constituting a complex fouling layer on the membrane surface in the first MD stage. In contrast, the membrane permeability and fouling of the second MD were not affected by feed pH adjustment because only volatiles passed through the first MD. More importantly, it was estimated that ITMD could obtain high-quality water and recover high-purity ammonium from LFL with relatively low ammonium concentration at an input cost of $ 2-3/m³, which was very competitive with existing techniques. These results demonstrated that the ITMD can be a valuable candidate strategy for simultaneous water purification and nutrient recovery from landfill leachate.

Tracking of Intestinal Probiotics In Vivo by NIR-IIb Fluorescence Imaging

The ability to accurately characterize microorganism distribution in the intestinal tract is helpful for understanding intrinsic mechanisms. Within the intestine, traditional optical probes used for microorganism labeling commonly suffer from a low imaging penetration depth and poor resolution. We report a novel observation tool useful for microbial research by labeling near-infrared-IIb (NIR-IIb, 1500-1700 nm) lanthanide nanomaterials NaGdF4:Yb3+,Er3+@NaGdF4,Nd3+ (Er@Nd NPs) onto the surface of Lactobacillus bulgaricus (L. bulgaricus) via EDC-NHS chemistry. We monitor microorganisms in tissue by two-photon excitation (TPE) microscopy and in vivo with NIR-IIb imaging. This dual-technique approach offers great potential for determining the distribution of transplanted bacteria in the intestinal tract with a higher spatiotemporal resolution.

Textile wastewater phytoremediation using Spirodela polyrhiza (L.) Schleid. assisted by novel bacterial consortium in a two-step remediation system

The study aims at developing a phyto-microremediation system for textile wastewater treatment using Spirodela polyrhiza (L.) Schleid. and a consortium of bacterial strains isolated from textile wastewater-contaminated matrices and rhizosphere of S. polyrhiza. The sequential phyto-microremediation of textile wastewater was carried out utilizing two-stage phyto-microremediation systems I [phytoremediation system (Stage 1) preceded microremediation system (Stage 2)] and II [microremediation system (Stage 1) preceded phytoremediation system (Stage 2)]. Pseudomonas stutzeri, Janibacter anophelis, Bacillus safensis, Bacillus pumilus, Bacillus thuringiensis, and Bacillus cereus constituted the bacterial consortium that was involved in the microremediation of textile wastewater. Biochemical characterization of Spirodela on exposure to untreated textile wastewater showed cadmium and nickel uptake as 26.03 and 22.99 mg g^-1 dw^-1. S. polyrhiza exhibited anatomical changes like distortion in the structure of the xylem, phloem, lower epidermis, and increased aerenchyma formation when remediating textile wastewater. The textile wastewater bioremediation in phyto-microremediation system I gives final reduction of COD 77.36%, color 91.70%, calcium 61.65%, iron 69.41%, nickel 89.30%, cadmium 88.37%, nitrate 70.83%, phosphate 73.11%, and sulfate 75.49%. Further, LC-MS analysis of treated wastewater from phyto-microremediation system I have shown biotransformation of metabolites into simpler compounds like 2-{Bis [4-(2-cyanophenoxy)phenyl]methyl}benzoic acid (C₃₄H₂₂N₂O₄). The FTIR spectrum of bacterial biomass exposed to textile wastewater exhibits substantial shifts of various bands in the IR region for functional groups such as alcohol, alkene, esters, azide, and amine as compared to non-exposed biomass.

Effect of different phosphate sources on uranium biomineralization by the Microbacterium sp. Be9 strain: A multidisciplinary approach study

Introduction

Industrial activities related with the uranium industry are known to generate hazardous waste which must be managed adequately. Amongst the remediation activities available, eco-friendly strategies based on microbial activity have been investigated in depth in the last decades and biomineralization-based methods, mediated by microbial enzymes (e.g., phosphatase), have been proposed as a promising approach. However, the presence of different forms of phosphates in these environments plays a complicated role which must be thoroughly unraveled to optimize results when applying this remediation process.

Methods

In this study, we have looked at the effect of different phosphate sources on the uranium (U) biomineralization process mediated by Microbacterium sp. Be9, a bacterial strain previously isolated from U mill tailings. We applied a multidisciplinary approach (cell surface characterization, phosphatase activity, inorganic phosphate release, cell viability, microscopy, etc.).

Results and Discussion

It was clear that the U removal ability and related U interaction mechanisms by the strain depend on the type of phosphate substrate. In the absence of exogenous phosphate substrate, the cells interact with U through U phosphate biomineralization with a 98% removal of U within the first 48 h. However, the U solubilization process was the main U interaction mechanism of the cells in the presence of inorganic phosphate, demonstrating the phosphate solubilizing potential of the strain. These findings show the biotechnological use of this strain in the bioremediation of U as a function of phosphate substrate: U biomineralization (in a phosphate free system) and indirectly through the solubilization of orthophosphate from phosphate (P) containing waste products needed for U precipitation.

Coupled effect of microbiologically induced calcium carbonate and biofilms in leachate

Fouling and clogging are persistent challenges to the collection and treatment of leachate. The main components of fouling and clogging are calcium carbonate (CaCO₃) and biofilms. However, the relationships between CaCO₃ and biofilms remain to be clarified. In this study, the interaction between microbially induced CaCO₃ precipitation (MICP) and biofilms was investigated using Luria-Bertani (LB) or urea media. Results showed that the bacteria promoted the precipitation of CaCO₃ and the formation of a complex mixture of biofilms. The amount of formed CaCO₃ in the urea medium was 12.9 times of that in the LB medium. The high MICP potential in the urea medium was associated with increased pH and alkalinity. In addition, the clogging materials exhibited a layered structure and uneven distribution over the clogging width and depth profile. These results indicated the presence of nucleation sites of CaCO₃ on the surface of and inside the bacteria. This research provides insights into the regulation of MICP and biofilms through dynamic control of clogging and fouling.

Peptidoglycan as major binding motif for Uranium bioassociation on Magnetospirillum magneticum AMB-1 in contaminated waters

The U(VI) bioassociation on Magnetospirillum magneticum AMB-1 cells was investigated using a multidisciplinary approach combining wet chemistry, microscopy, and spectroscopy methods to provide deeper insight into the interaction of U(VI) with bioligands of Gram-negative bacteria for a better molecular understanding. Our findings suggest that the cell wall plays a prominent role in the bioassociation of U(VI). In time-dependent bioassociation studies, up to 95 % of the initial U(VI) was removed from the suspension and probably bound on the cell wall within the first hours due to the high removal capacity of predominantly alive Magnetospirillum magneticum AMB-1 cells. PARAFAC analysis of TRLFS data highlights that peptidoglycan is the most important ligand involved, showing a stable immobilization of U(VI) over a wide pH range with the formation of three characteristic species. In addition, in-situ ATR FT-IR reveals the predominant strong binding to carboxylic functionalities. At higher pH polynuclear species seem to play an important role. This comprehensive molecular study may initiate in future new remediation strategies on effective immobilization of U(VI). In combination with the magnetic properties of the bacteria, a simple technical water purification process could be realized not only for U(VI), but probably also for other heavy metals.

Fluorescence spectroscopy analysis of fly ash removal from aqueous systems: adsorption of alginate to silica and alumina

Fly ash is a toxic industrial waste, mainly consisting of silica and alumina particles, that has been found discharged into the environment. It is proposed that alginate, a naturally occurring biopolymer, can bind to these minerals and thus play a role in water purification. The binding forces involved in this process consist of weak interactions, such as van der Waals forces and electrostatic interactions. Although the attachment of alginate to mineral surfaces is mainly governed by its carboxylate groups, hydroxyl moieties could play a role in the interaction between the polymer and minerals. This work aims to use the SiO₂ and Al₂O₃ particles as models for fly ash and to show the use of alginate biopolymers (fluorescently labelled with an aminonaphthaline sulfonate fluorophore (AmNS)) to coagulate them. The addition of simple electrolytes like NaCl and CaCl₂ encourages the coiling of the polymer chain at high pH values which has an effect on its capability to bind to the inorganic particles. A combination of fluorescence and ICP-MS demonstrated that alginate has a considerable adsorption affinity for Al₂O₃, whereas it attracts SiO₂ weakly. The adsorption process is pH dependent: strong adsorption was observed at low pH values. The dependence of adsorption on the mineral (Al₂O₃ and SiO₂) concentration was also examined under different pH conditions: the adsorption amount was observed to increase by increasing the solid concentration. Adsorption isotherms obtained at low and high mineral concentrations were found to be Henry in type.

Calcium ion biorecovery from industrial wastewater by Bacillus amyloliquefaciens DMS6

Calcium ions in industrial wastewater needs to be removed to prevent the production of limescale, which can have negative consequences. Biomineralization has become the focus due to its lower costs than traditional methods of remediation. In this study, calcium ions were bio-precipitated under the action of free and immobilized Bacillus amyloliquefaciens DMS6 bacteria, and the calcium ion removal efficiency was also compared. The results show that it only needed 3 days to decrease the calcium ion concentration to an ideal level of 76-116 mg/L under the action of DMS6 bacteria immobilized by activated carbon fiber, with calcium ion removal ratios reaching 99%-95% by the 7^th day. DMS6 bacteria immobilized by activated carbon fiber were superior to free bacteria and bacteria immobilized by sodium alginate in calcium ion removal. Calcium ions are biomineralized into calcite, Mg-rich calcite, aragonite and monohydrocalcite with abundant organic functional groups, 4 types of secondary protein structures, amino acids, phospholipids, negative stable carbon isotope δ¹³C_PDB values (-16.68‰ to-17.25‰) and negatively charged biomineral surface. Calcium ions were diffused into cells and took part in the intracellular biomineralization of monohydrocalcite, also facilitating calcium ion removal. The formation of intracellular monohydrocalcite has rarely been reported. This study demonstrates an economic and environmentally friendly method to remove calcium ions from industrial wastewater.

Au(III)-induced extracellular electron transfer by Burkholderia contaminans ZCC for the bio-recovery of gold nanoparticles

The biorecovery of gold (Au) by microbial reduction has received increasing attention, however, the biomolecules involved and the mechanisms by which they operate to produce Au nanoparticles have been not resolved. Here we report that Burkholderia contaminans ZCC is capable of reduction of Au(III) to Au nanoparticles on the cell surface. Exposure of B. contaminans ZCC to Au(III) led to significant changes in the functional group of cell proteins, with approximately 11.1% of the (C-C/C-H) bonds being converted to CO (8.1%) and C-OH (3.0%) bonds and 29.4% of the CO bonds being converted to (C-OH/C-O-C/P-O-C) bonds, respectively. In response to Au(III), B. contaminans ZCC also displayed the ability of extracellular electron transfer (EET) via membrane proteins and could produce reduced riboflavin as verified by electrochemical and liquid chromatography-mass spectrometric results, but did not do so without Au(III) being present. Addition of exogenous reduced riboflavin to the medium suggested that B. contaminans ZCC could utilize indirect EET via riboflavin to enhance the rate of reduction of Au(III). Transcriptional analysis of the riboflavin genes (ribBDEFH) supported the view of the importance of riboflavin in the reduction of Au(III) and its importance in the biorecovery of gold.

Aggregation performance and adhesion behavior of microbes in response to feast/famine condition: Rapid granulation of aerobic granular sludge

Periodic starvation was a common strategy for the rapid start-up of aerobic granular sludge (AGS), and investigating the behavior of microbes that originated from inner or outer layer in response to feast/famine condition could provide more details for the development or stability of AGS. In this work, the microbes of the AGS were isolated by layers, the aggregation of microbes, the adhesion behavior of microbes, and viscoelasticity of the layer formed by microbes, at feast/famine conditions, were investigated for the in-depth understanding of the start-up and stability of AGS. The famine condition reduced the negative charge and deprotonated carboxyl groups of the surface thereby boosting the aggregation and adhesion of microbes. The feast condition was more beneficial for the stability of the layer as it caused a denser layer of microbes. The inner core microbes (IC) presented a higher aggregation rate than the outer layer microbes (OL) at feast/famine conditions. Also, the IC presented the highest aggregation rate, adhesion rate, and adhesion mass at famine conditions, which was most in favor of the start-up stage of the aerobic granulation. Since the denser layer was formed by IC, IC had better advantages over OL at the famine stage in the formation of a more stable layer. This study affirmed the role of microbes in the inner layer of the granule during the start-up phase and provided a theoretical basis for understanding the significance of the famine period for rapid granulation.

Cell components, interaction types and functional groups involved in the in vitro binding of bisphenol A by Lactiplantibacillus plantarum RS20D and DL7X

AIMS

The current study aimed to evaluate the capacity of two Lactiplantibacillus plantarum strains to remove Bisphenol A (BPA) and to determine the preliminary removal mechanisms underlying this process.

METHODS AND RESULTS

The BPA removal capacity of L. plantarum RS20D and DL7X was assessed by HPLC analysis. The effect of various treatments (physical, chemical, and enzymatic) on two strains were studied to understand which interaction types worked. The different cellular components of them were also subjected to binding assays. Additionally, Fourier-transform infrared spectroscopy (FTIR) was performed to identify the functional groups related to the BPA binding process. Results show that various treatments enhanced the binding capacity of two strains, the effect of sodium dodecyl sulfate was the most outstanding (P=0.000, P=0.000). Hydrogen bonding and hydrophobic interactions likely occurred. Peptidoglycans showed the highest binding capability, protoplasts and teichoic acids might also exert a binding effect. -OH, C=O, -CH, -NH, C-N, C-O, and P=O participated in BPA binding by the two L. plantarum lines.

CONCLUSIONS

Peptidoglycans, protoplasts, and teichoic acid played a vital role in the binding of BPA.

SIGNIFICANCE AND IMPACT OF THE STUDY

Our results provided a theoretical foundation for developing effective dietary strategies with foodborne L. plantarum to remove food contaminants.

How humic acid and Tween80 improve the phenanthrene biodegradation efficiency: Insight from cellular characteristics and quantitative proteomics

Polycyclic aromatic hydrocarbons (PAHs) are toxic and recalcitrant pollutants, with an urgent need for bioremediation. Systematic biodegradation studies show that surfactant-mediated bioremediation is still poorly understood. Here, we investigated a comprehensive cellular response pattern of the PAH degrading strain B. subtilis ZL09-26 to (non-)green surfactants at the cellular and proteomic levels. Eight characteristic cellular factor investigations and detailed quantitative proteomics analyses were performed to understand the highly enhanced phenanthrene (PHE) degradation efficiency (2.8- to 3-fold improvement) of ZL09-26 by humic acid (HA) or Tween80. The commonly upregulated pathway and proteins (Arginine generation, LacI-family transcriptional regulator, and Lactate dehydrogenase) and various metabolic pathways (such as phenanthrene degradation upstream pathway and central carbon metabolism) jointly govern the change of cellular behaviors and improvement of PHE transport, emulsification, and degradation in a network manner. The obtained molecular knowledge empowers engineers to expand the application of surfactants in the biodegradation of PAHs and other pollutants.

Inheritance of physico-chemical properties and ROS generation by carbon quantum dots derived from pyrolytically carbonized bacterial sources

Bacteria are frequently used in industrial processes and nutrient supplementation to restore a healthy human microflora, but use of live bacteria is often troublesome. Here, we hypothesize that bacterially-derived carbon-quantum-dots obtained through pyrolytic carbonization inherit physico-chemical properties from probiotic and pathogenic source-bacteria. Carbon-quantum-dots carbonized at reaction-temperatures below 200 ​°C had negligible quantum-yields, while temperatures above 220 ​°C yielded poor water-suspendability. Fourier-transform infrared-spectroscopy demonstrated preservation of amide absorption bands in carbon-quantum-dots derived at intermediate temperatures. X-ray photoelectron-spectroscopy indicated that the at%N in carbon-quantum-dots increased with increasing amounts of protein in source-bacterial surfaces. Carbonization transformed hydrocarbon-like bacterial surface compounds into heterocyclic aromatic-carbon structures, evidenced by a broad infrared absorption band (920-900 ​cm⁻¹) and the presence of carbon in C–C functionalities of carbon-quantum-dots. The chemical composition of bacterially-derived carbon-quantum-dots could be explained by the degradation temperatures of main bacterial cell surface compounds. All carbon-quantum-dots generated reactive-oxygen-species, most notably those derived from probiotic lactobacilli, carrying a high amount of surface protein. Concluding, amide functionalities in carbon-quantum-dots are inherited from surface proteins of source-bacteria, controlling reactive-oxygen-species generation. This paves the way for applications of bacterially-derived carbon-quantum-dots in which reactive-oxygen-species generation is essential, instead of hard-to-use live bacteria, such as in food supplementation or probiotic-assisted antibiotic therapy.

•

Pyrolytic carbonization of bacteria between 200°C and 220°C yields water-suspendable CQDs.

•

Bacterially-derived CQDs inherit amide functionalities from bacterial cell surface proteins.

•

Hydrocarbon-like bacterial surface compounds give heterocyclic aromatic-carbon structures in bacterially-derived CQDs.

•

Bacterially-derived CQDs possess graphitic nitrogen.

•

Zeta potentials of CQDs relate with nitrogen occurrence in CQDs.

Synergy between "Probiotic" Carbon Quantum Dots and Ciprofloxacin in Eradicating Infectious Biofilms and Their Biosafety in Mice

Orally administrated probiotic bacteria can aid antibiotic treatment of intestinal infections, but their arrival at their intestinal target site is hampered by killing in the gastrointestinal tract and by antibiotics solely intended for pathogen killing. Carbon-quantum-dots are extremely small nanoparticles and can be derived from different sources, including bacteria. Here, we hypothesize that carbon-quantum-dots inherit antibacterial activity from probiotic source bacteria to fulfill a similar role as live probiotics in intestinal infection therapy. Physico-chemical analyses indicated that carbon-quantum-dots, hydrothermally derived from Bifidobacterium breve (B-C-dots), inherited proteins and polysaccharides from their source-bacteria. B-C-dots disrupted biofilm matrices of Escherichia coli and Salmonella typhimurium biofilms through extensive reactive-oxygen-species (ROS)-generation, causing a decrease in volumetric bacterial-density in biofilms. Decreased bacterial densities leave more open space in biofilms and have enhanced ciprofloxacin penetration and killing potential in an E. coli biofilm pre-exposed to probiotic B-C-dots. Pathogenic carbon-quantum-dots hydrothermally derived from E. coli (E-C-dots) did not disrupt pathogenic biofilms nor enhance E. coli killing potential by ciprofloxacin. B-C-dots were biosafe in mice upon daily administration, while E-C-dots demonstrated a decrease in white blood cell and platelet counts and an increase in C-reactive protein levels. Therefore, the way is paved for employing probiotic carbon-quantum-dots instead of viable, probiotic bacteria for synergistic use with existing antibiotics in treating intestinal infections.

Characterisation of Microparticle Waste from Dental Resin-Based Composites

Clinical applications of resin-based composite (RBC) generate environmental pollution in the form of microparticulate waste. Methods: SEM, particle size and specific surface area analysis, FT-IR and potentiometric titrations were used to characterise microparticles arising from grinding commercial and control RBCs as a function of time, at time of generation and after 12 months ageing in water. The RBCs were tested in two states: (i) direct-placement materials polymerised to simulate routine clinical use and (ii) pre-polymerised CAD/CAM ingots milled using CAD/CAM technology. Results: The maximum specific surface area of the direct-placement commercial RBC was seen after 360 s of agitation and was 1290 m²/kg compared with 1017 m²/kg for the control material. The median diameter of the direct-placement commercial RBC was 6.39 μm at 360 s agitation and 9.55 μm for the control material. FTIR analysis confirmed that microparticles were sufficiently unique to be identified after 12 months ageing and consistent alteration of the outermost surfaces of particles was observed. Protonation-deprotonation behaviour and the pH of zero proton charge (pH_zpc) ≈ 5–6 indicated that the particles are negatively charged at neutral pH7. Conclusion: The large surface area of RBC microparticles allows elution of constituent monomers with potential environmental impacts. Characterisation of this waste is key to understanding potential mitigation strategies.

Effect of growth conditions on cell wall composition and cadmium adsorption in Chlorella vulgaris: A new approach to biosorption research

Biosorption of toxic metals in microalgae is a process relying on the presence of cell wall reactive groups acting as binding sites. This work studied the effect of culture conditions on the outer cell wall composition of C. vulgaris and cadmium biosorption. The experiments were conducted in continuous culture under light and nitrogen limitation at two growth rates (0.4 and 0.2 d^-1). Functional groups were profiled using ATR-FTIR spectrometry, and total cadmium biosorption was assayed. Significant differences in composition were attested the most salient being the absence of carboxyl groups in the light deprived states and a larger number of carbohydrates and amino groups in the nitrogen deprived cultures, particularly amino groups from deacetylated D-glucosamine polysaccharides. Higher biosorption was obtained with the nitrogen-restricted biomass, reaching a maximum of 11.9 mg_Cd/g_biomass, as compared to a minimum of 8.0 mg_Cd/g_biomass achieved in the light-restricted states. The increased biosorption exhibited by nitrogen-restricted strains was attributed to the deacetylated amino groups that have enhanced cation affinity. This work has shown that the characteristics of the outer cell wall can be engineered by culture conditions to improve biosorption, providing a new approach that opens up new research frontiers for the biosorption of hazardous metals.

X-Ray Photoelectron Spectroscopy on Microbial Cell Surfaces: A Forgotten Method for the Characterization of Microorganisms Encapsulated With Surface-Engineered Shells

Encapsulation of single microbial cells by surface-engineered shells has great potential for the protection of yeasts and bacteria against harsh environmental conditions, such as elevated temperatures, UV light, extreme pH values, and antimicrobials. Encapsulation with functionalized shells can also alter the surface characteristics of cells in a way that can make them more suitable to perform their function in complex environments, including bio-reactors, bio-fuel production, biosensors, and the human body. Surface-engineered shells bear as an advantage above genetically-engineered microorganisms that the protection and functionalization added are temporary and disappear upon microbial growth, ultimately breaking a shell. Therewith, the danger of creating a "super-bug," resistant to all known antimicrobial measures does not exist for surface-engineered shells. Encapsulating shells around single microorganisms are predominantly characterized by electron microscopy, energy-dispersive X-ray spectroscopy, Fourier transform infrared spectroscopy, particulate micro-electrophoresis, nitrogen adsorption-desorption isotherms, and X-ray diffraction. It is amazing that X-ray Photoelectron Spectroscopy (XPS) is forgotten as a method to characterize encapsulated yeasts and bacteria. XPS was introduced several decades ago to characterize the elemental composition of microbial cell surfaces. Microbial sample preparation requires freeze-drying which leaves microorganisms intact. Freeze-dried microorganisms form a powder that can be easily pressed in small cups, suitable for insertion in the high vacuum of an XPS machine and obtaining high resolution spectra. Typically, XPS measures carbon, nitrogen, oxygen and phosphorus as the most common elements in microbial cell surfaces. Models exist to transform these compositions into well-known, biochemical cell surface components, including proteins, polysaccharides, chitin, glucan, teichoic acid, peptidoglycan, and hydrocarbon like components. Moreover, elemental surface compositions of many different microbial strains and species in freeze-dried conditions, related with zeta potentials of microbial cells, measured in a hydrated state. Relationships between elemental surface compositions measured using XPS in vacuum with characteristics measured in a hydrated state have been taken as a validation of microbial cell surface XPS. Despite the merits of microbial cell surface XPS, XPS has seldom been applied to characterize the many different types of surface-engineered shells around yeasts and bacteria currently described in the literature. In this review, we aim to advocate the use of XPS as a forgotten method for microbial cell surface characterization, for use on surface-engineered shells encapsulating microorganisms.

The importance of the bacterial cell wall in uranium(VI) biosorption

The bacterial cell envelope, in particular the cell wall, is considered the main controlling factor in the biosorption of aqueous uranium(vi) by microorganisms. However, the specific roles of the cell wall, associated biomolecules, and other components of the cell envelope are not well defined. Here we report findings on the biosorption of uranium by isolated cell envelope components and associated biomolecules, with P. putida 33015 and B. subtilis 168 investigated as representative strains for the differences in Gram-negative and Gram-positive cell envelope architecture, respectively. The cell wall and cell surface membrane were isolated from intact cells and characterised by X-ray Photoelectron Spectroscopy (XPS) and Attenuated Total Reflectance-Fourier Transform Infrared (ATR-FT-IR) spectroscopy; revealing variations in the abundance of functional moieties and biomolecules associated with components of the cell envelope. Uranium biosorption was investigated as a function of cell envelope component and pH, comparing with intact cells. The isolated cell wall from both strains exhibited the greatest uranium biosorption capacity. Deprotonation of favourable functional groups on the biomass as the pH increased from 3 to 5.5 increased their uranium biosorption capacity by approximately 3 fold. The results from ATR-FT-IR indicated that uranium(vi) biosorption was mediated by phosphate and carboxyl groups associated with proteins and phosphorylated biopolymers of the cell envelope. This includes outer membrane phospholipids and LPS of Gram-negative bacteria and teichoic acids, surface proteins and peptidoglycan from Gram-positive bacteria. As a result, the biosorption process of uranium(vi) to microorganisms is controlled by surface interactions, resulting in higher accumulation of uranium in the cell envelope. This demonstrates the importance of bacterial cell wall as the key mediator of uranium biosorption with microorganisms.

New Tools for Imaging Neutrophils: Work Function Mapping and Element-Specific, Label-Free Imaging of Cellular Structures

Photoemission electron microscopy and imaging X-ray photoelectron spectroscopy are today frequently used to obtain chemical and electronic states, chemical shifts, work function profiles within the fields of surface- and material sciences. Lately, because of recent technological advances, these tools have also been valuable within life sciences. In this study, we have investigated the power of photoemission electron microscopy and imaging X-ray photoelectron spectroscopy for visualization of human neutrophil granulocytes. These cells, commonly called neutrophils, are essential for our innate immune system. We hereby investigate the structure and morphology of neutrophils when adhered to gold and silicon surfaces. Energy-filtered imaging of single cells are acquired. The characteristic polymorphonuclear cellular nuclei divided into 2-5 lobes is visualized. Element-specific imaging is achieved based on O 1s, P 2p, C 1s, Si 2p, and N 1s core level spectra, delivering elemental distribution with submicrometer resolution, illustrating the strength of this type of cellular morphological studies.

Biosorption behavior and mechanism of cadmium from aqueous solutions by Synechocystis sp. PCC6803

Cyanobacteria are promising adsorbents that are widely used for heavy metal removal in aqueous solutions. However, the underlying adsorption mechanism of Synechocystis sp. PCC6803 is currently unclear. In this study, the adsorption behavior and mechanism of cadmium (Cd²⁺) were investigated. Batch biosorption experiments showed that the optimal adsorption conditions were pH 7.0, 30 °C, 15 min, and an initial ion concentration of 4.0 mg L⁻¹. The adsorption process fitted well with the pseudo-second order kinetic model, mainly based on chemisorption. Complexation of Cd²⁺ with carboxyl, hydroxyl, carbonyl, and amido groups was demonstrated by Fourier-transform infrared spectroscopy (FTIR), Raman spectroscopy and X-ray photoelectron spectroscopy (XPS) analyses. Scanning electron microscopy (SEM), transmission electron microscopy (TEM), and energy-dispersive X-ray spectrometry (EDX) analyses confirmed the presence of Cd²⁺ on the cyanobacterial cell surface and intracellularly. Cd²⁺ could lead to reactive oxygen species (ROS) accumulation and photosynthesis inhibition in cyanobacterial cells, and glutathione (GSH) played an important role in alleviating Cd²⁺ toxicity. Analyses of three-dimensional fluorescence spectroscopy (3D-EEM) and high performance anion exchange chromatography-pulsed amperometric detection (HPAEC-PAD) revealed the changes of the composition and content of EPS after Cd²⁺ adsorption, respectively. Real-time quantitative polymerase chain reaction (RT-qPCR) revealed the potential molecular regulatory mechanisms involved in Cd²⁺ biosorption. These results revealed the adsorption mechanism of Cd²⁺ by Synechocystis sp. PCC6803 and provided theoretical guidance for insight into the biosorption mechanisms of heavy metals by other strains.

The results of extracellular polymeric substances (EPS) extraction, physiological and biochemical determination and gene expression revealed the adsorption mechanism of Synechocystis sp. PCC6803 under cadmium stress.

Molecular Binding of EuIII/CmIII by Stenotrophomonas bentonitica and Its Impact on the Safety of Future Geodisposal of Radioactive Waste

Microbial communities occurring in reference materials for artificial barriers (e.g., bentonites) in future deep geological repositories of radioactive waste can influence the migration behavior of radionuclides such as curium (Cm^III). This study investigates the molecular interactions between Cm^III and its inactive analogue europium (Eu^III) with the indigenous bentonite bacterium Stenotrophomonas bentonitica at environmentally relevant concentrations. Potentiometric studies showed a remarkably high concentration of phosphates at the bacterial cell wall compared to other bacteria, revealing the great potential of S. bentonitica for metal binding. Infrared spectroscopy (ATR-FTIR) and X-ray photoelectron spectroscopy (XPS) confirmed the role of phosphates and carboxylate groups from the cell envelope in the bioassociation of Eu^III. Additionally, time-resolved laser-induced fluorescence spectroscopy (TRLFS) identified phosphoryl and carboxyl groups from bacterial envelopes, among other released complexing agents, to be involved in the Eu^III and Cm^III coordination. The ability of this bacterium to form a biofilm at the surface of bentonites allows them to immobilize trivalent lanthanide and actinides in the environment.

Biofilm Producing Rhizobacteria With Multiple Plant Growth-Promoting Traits Promote Growth of Tomato Under Water-Deficit Stress

Plant growth-promoting rhizobacteria (PGPR) not only enhance plant growth but also control phytopathogens and mitigate abiotic stresses, including water-deficit stress. In this study, 21 (26.9%) rhizobacterial strains isolated from drought-prone ecosystems of Bangladesh were able to form air–liquid (AL) biofilms in the glass test tubes containing salt-optimized broth plus glycerol (SOBG) medium. Based on 16S rRNA gene sequencing, Pseudomonas chlororaphis (ESR3 and ESR15), P. azotoformans ESR4, P. poae ESR6, P. fluorescens (ESR7 and ESR25), P. gessardii ESR9, P. cedrina (ESR12, ESR16, and ESR23), P. veronii (ESR13 and ESR21), P. parafulva ESB18, Stenotrophomonas maltophilia ESR20, Bacillus cereus (ESD3, ESD21, and ESB22), B. horikoshii ESD16, B. aryabhattai ESB6, B. megaterium ESB9, and Staphylococcus saprophyticus ESD8 were identified. Fourier transform infrared spectroscopy studies showed that the biofilm matrices contain proteins, polysaccharides, nucleic acids, and lipids. Congo red binding results indicated that these bacteria produced curli fimbriae and nanocellulose-rich polysaccharides. Expression of nanocellulose was also confirmed by Calcofluor binding assays and scanning electron microscopy. In vitro studies revealed that all these rhizobacterial strains expressed multiple plant growth-promoting traits including N₂ fixation, production of indole-3-acetic acid, solubilization of nutrients (P, K, and Zn), and production of ammonia, siderophores, ACC deaminase, catalases, lipases, cellulases, and proteases. Several bacteria were also tolerant to multifarious stresses such as drought, high temperature, extreme pH, and salinity. Among these rhizobacteria, P. cedrina ESR12, P. chlororaphis ESR15, and B. cereus ESD3 impeded the growth of Xanthomonas campestris pv. campestris ATCC 33913, while P. chlororaphis ESR15 and B. cereus ESD21 prevented the progression of Ralstonia solanacearum ATCC^® 11696^TM. In a pot experiment, tomato plants inoculated with P. azotoformans ESR4, P. poae ESR6, P. gessardii ESR9, P. cedrina ESR12, P. chlororaphis ESR15, S. maltophilia ESR20, P. veronii ESR21, and B. aryabhattai ESB6 exhibited an increased plant growth compared to the non-inoculated plants under water deficit-stressed conditions. Accordingly, the bacterial-treated plants showed a higher antioxidant defense system and a fewer tissue damages than non-inoculated plants under water-limiting conditions. Therefore, biofilm-producing PGPR can be utilized as plant growth promoters, suppressors of plant pathogens, and alleviators of water-deficit stress.

Cadmium Immobilization in the Rhizosphere and Plant Cellular Detoxification: Role of Plant-Growth-Promoting Rhizobacteria as a Sustainable Solution

Food is the major cadmium (Cd)-exposure pathway from agricultural soils to humans and other living entities and must be reduced in an effective way. A plant can select beneficial microbes, like plant-growth-promoting rhizobacteria (PGPR), depending upon the nature of root exudates in the rhizosphere, for its own benefits, such as plant growth promotion as well as protection from metal toxicity. This review intends to seek out information on the rhizo-immobilization of Cd in polluted soils using the PGPR along with plant nutrient fertilizers. This review suggests that the rhizo-immobilization of Cd by a combination of PGPR and nanohybrid-based plant nutrient fertilizers would be a potential and sustainable technology for phytoavailable Cd immobilization in the rhizosphere and plant cellular detoxification, by keeping the plant nutrition flow and green dynamics of plant nutrition and boosting the plant growth and development under Cd stress.

Competitive adsorption of heavy metals by anaerobic ammonium-oxidizing (anammox) consortia

Anammox-based processes and microbial consortia have drawn extensive attention for their use in high-efficiency wastewater treatment technologies. Metals substantially affect the activity of anammox consortia and the quality of wastewater treatment plant effluent. Here, we explored the role of anammox consortia in terms of metals complexation in both single and multi-metal systems. Adsorption edges of single metal cations indicate that the adsorption preference was in the order: Pb(II) > Cd(II) > Cr(VI). A competitive effect was observed in multi-metal cations systems, with Pb(II) being preferably adsorbed and the degree of adsorption somewhat reduced in the presence of either Cd(II) or Cr(VI), while Cd(II) and Cr(VI) were easily exchanged and substituted by other metals. Fourier transform infrared (FTIR) and X-ray photoelectron spectroscopy (XPS) further suggest that the adsorption of Pb(II) and Cd(II) are as inner-sphere ion-exchange mechanisms, while Cr(VI) adsorption is mainly by outer-sphere complexation. Density functional theory (DFT) calculations highlight that Cd(II) and Pb(II) have different binding sites compared to Cr(VI), and the order of binding energy (E_bd) of three metal cations were Pb(II) > Cd(II) > Cr(VI). These calculations support the adsorption data in that Pb forms more stable complexes with anammox bacterial surface ligands. Surface complexation modelling (SCM) further predicted both the sorption of single metal cations and competitive adsorption of the three metals to anammox consortia, the exception being Cd at higher loadings. The results of this study highlight the potential role of anammox consortia in removing metal cations from wastewater in treatment systems.

Microwave-Assisted Synthesis of Hollow Microspheres with Multicomponent Nanocores for Heavy-Metal Removal and Magnetic Sensing

The primary advantage of a hollow structure is the likelihood of introducing diverse components in a single particle to achieve multiple missions. Herein, hollow microspheres with multicomponent nanocores (HMMNs) have been prepared based on a template-free strategy via a microwave-assisted hydrothermal treatment of Chlorella. The resulting HMMNs retain the near-spherical hollow morphology and functional groups of the cell wall of Chlorella, obviating the need for templates and chemical modification. The elements (iron, cobalt, calcium, magnesium, chlorine, and phosphorus) naturally present within the Chlorella cells react to form hydroxyapatite/chlorapatite and magnetic nanocores without the need for exogenous chemical reagents. The performances of HMMNs for cadmium ion (Cd²⁺) removal and antibiotic detection are explored. HMMNs exhibit relatively high adsorbance of Cd²⁺ (1035.8 mmol/kg) and can be easily recovered by application of an external magnetic field. Ion exchange with Ca²⁺ and Mg²⁺ is shown to be the main mechanism of Cd²⁺ elimination. In addition, HMMNs are a suitable carrier for the construction of a magnetic immunosensor, as demonstrated by the successful development of such an immunosensor with acceptable analytical performance for the detection of neomycin in milk samples. The versatile applications of HMMNs result from their multicomponent nanocores, hollow structure, and the functional groups on their shell. This work not only offers a simple and eco-friendly strategy for the fabrication of novel HMMNs but also provides a valuable advanced material for contaminant detection and heavy-metal removal.

High-efficient microbial immobilization of solved U(VI) by the Stenotrophomonas strain Br8

The environmental impact of uranium released during nuclear power production and related mining activity is an issue of great concern. Innovative environmental-friendly water remediation strategies, like those based on U biomineralization through phosphatase activity, are desirable. Here, we report the great U biomineralization potential of Stenotrophomonas sp. Br8 CECT 9810 over a wide range of physicochemical and biological conditions. Br8 cells exhibited high phosphatase activity which mediated the release of orthophosphate in the presence of glycerol-2-phosphate around pH 6.3. Mobile uranyl ions were bioprecipitated as needle-like fibrils at the cell surface and in the extracellular space, as observed by Scanning Transmission Electron Microscopy (STEM). Extended X-Ray Absorption Fine Structure (EXAFS) and X-Ray Diffraction (XRD) analyses showed the local structure of biogenic U precipitates to be similar to that of meta-autunite. In addition to the active U phosphate biomineralization process, the cells interact with this radionuclide through passive biosorption, removing up to 373 mg of U per g of bacterial dry biomass. The high U biomineralization capacity of the studied strain was also observed under different conditions of pH, temperature, etc. Results presented in this work will help to design efficient U bioremediation strategies for real polluted waters.

Importance of exopolysaccharide branched chains in determining the aggregation ability of anammox sludge

The high aggregation ability of anammox granular sludge is an issue of wide concern; however, the mechanism needs to be further clarified. In this study, selective hydrolysis experiments were performed to determine the role of exopolysaccharide (PS) branched chains and proteins for the aggregation mechanism of anammox granular sludge. The results revealed that selective hydrolysis of proteins hardly affected the granular aggregation while the hydrolysis of PS branched chains led to a decrease in the sludge zeta potential by 17.3% (β-amylase group) and 24.1% (isoamylase group), a decrease of hydrophobicity by 11.6% (β-amylase group) and 17.7% (isoamylase group), an increase of surface free energy by 36.8% (β-amylase group) and 55.1% (isoamylase group) and the deterioration of the PS self-assembly ability. In addition, FTIR and XPS spectra analysis showed that the disruption of PS branched chains resulted in a higher proportion of hydrophilic and electronegative groups, which hindered bacterial aggregation, which was further confirmed by XDLVO theory. The key role of the PS chain structure in sludge aggregation is a critical finding of this work that provides helpful insights for the application of anammox process.

The branched chains and branching degree of exopolysaccharides affecting the stability of anammox granular sludge

The effect of extracellular polysaccharides on the structural stability of granular sludge is widely recognized, and determining their mechanism of action on the stability of granules remains challenging. Herein, enzymatic experiments were used to systematically study the stability changes and internal mechanisms of anammox granular sludge following hydrolysis of extracellular proteins and polysaccharides (PS). The results revealed that the selective hydrolysis of the proteins hardly affected the stability of the granules, while the hydrolysis of the PS branched chains caused the granules to disintegrate. The hydrolysis of the PS chains in the EPS matrix decreased the degree of branching, width and height via nuclear magnetic resonance (NMR) spectroscopy and atomic force microscopy (AFM), and these parameters are closely related to granular stability. Moreover, scanning electron microscopy (SEM) showed a large number of pores and cracks on the granules, bacterial adhesion decreased, and the EPS adhered to the surface of the granules dissolved. The changes in the gel characteristics of the granules were studied by rheology, and the mechanical strength and viscosity of the granular sludge decreased. For the surface characteristics of granules, the zeta potential and hydrophobicity both decreased, revealing that changes in the branched-chain configuration of the PS and the degree of branching caused granular disintegration. Spectral analysis showed that the hydrolysis of the branch points and the branched glycosides of PS led to a higher proportion of hydrophilic and electronegative groups in the EPS matrix, which hindered bacterial aggregation and reduced anammox granule stability. This investigation clarifies the impact of the branched-chain configuration of the PS and their degree of branching on anammox granule stability, which will promote the further application of anammox granules.

Cell surface-expression of the phosphate-binding protein PstS: System development, characterization, and evaluation for phosphorus removal and recovery

Simultaneous overabundance and scarcity of inorganic phosphate (P_i) is a critical issue driving the development of innovative water/wastewater treatment technologies that not only facilitate P_i removal to prevent eutrophication, but also recover P_i for agricultural reuse. Here, a cell-surface expressed high-affinity phosphate binding protein (PstS) system was developed, and its P_i capture and release potential was evaluated. E. coli was genetically modified to express PstS on its outer membrane using the ice nucleation protein (INP) as an anchoring motif. Verification of protein expression and localization were performed utilizing SDS-polyacrylamide gel electrophoresis (SDS-PAGE), western blot, and outer membrane separation analyses. Cell surface characterization was investigated through acid-base titration, X-ray photoelectron spectroscopy (XPS), and Fourier transform infrared spectroscopy (FTIR). These tests provided information on the macromolecular structure and composition of the bacteria surface as well as the proton-exchange properties of the surface functional groups (i.e., pKa values). Phosphate desorption and adsorption batch experiments were conducted to evaluate the effects of temperature, pH, and ionic strength on phosphate capture and release. The PstS surface-displayed cells demonstrated greater potential to release and capture phosphate compared to non-modified cells. Higher temperatures up to 40°C, basic pH conditions (pH = 10.5), and higher ionic strength up to 1.0 mol/L KCl promoted 20%-50% higher phosphate release.

Infrared spectroscopy with multivariate analysis to interrogate the interaction of whole cells and secreted soluble exopolimeric substances of Pseudomonas veronii 2E with Cd(II), Cu(II) and Zn(II)

Extracellular polymeric substances (EPS) are bacterial products associated to cell wall or secreted to the liquid media that form the framework of microbial mats. These EPS contain functional groups as carboxyl, amino, hydroxyl, phosphate and sulfhydryl, able to interact with cations. Thus, EPS may be considered natural detoxifying compounds of metal polluted waters and wastewaters. In this work Attenuated Total Reflectance-Fourier Transform Infrared spectroscopy (ATR-FTIR) in combination with multivariate analysis (Principal Component Analysis-PCA-) were used to study the interaction of Cd(II), Cu(II) and Zn(II) and Pseudomonas veronii 2E cells, including bound EPS and cell wall, and its different soluble EPS fractions, previously characterized as Cd(II) ligands of moderate strength. Amino groups present in exopolysaccharide fraction were responsible for Zn(II) and Cu(II) complexation, while carboxylates chelated Cd(II). In lipopolysaccharide fraction, phosphoryl and carboxyl sites were involved in Cd(II) and Cu(II) binding, while Zn(II) interacted with amino groups. Similar results were obtained from cells. These studies confirmed that FTIR-PCA is a rapid analytical tool to provide valuable information regarding the functional groups in biomolecules related to metal interaction. Moreover, a discrimination and identification of functional groups present in both EPS and cells that interacted with Cd(II), Zn(II) and Cu(II) was demonstrated.

Effects of graphene oxide and reduced graphene oxide on acetoclastic, hydrogenotrophic and methylotrophic methanogenesis

This study describes the effects of graphene oxide (GO) and reduced graphene oxide (rGO) on the acetoclastic, hydrogenotrophic and methylotrophic pathways of methanogenesis by an anaerobic consortium. The results showed that GO negatively affected the hydrogenotrophic and acetoclastic pathways at a concentration of 300 mg/L, causing a decrease of ~ 38% on the maximum specific methanogenic activity (MMA) with respect to the controls lacking GO. However, the presence of rGO (300 mg/L) promoted an improvement of the MMA (> 45%) achieved with all substrates, except for the hydrogenotrophic pathway, which was relatively insensitive to rGO. The presence of either rGO or GO enhanced the methylotrophic pathway and resulted in an increase of the MMA of up to 55%. X-ray photoelectron spectroscopy (XPS) analysis revealed that GO underwent microbial reduction during the incubation period. Electrons derived from substrates oxidation were deviated from methanogenesis towards the reduction of GO, which may explain the MMA decreased observed in the presence of GO. Furthermore, XPS evidence indicated that the extent of GO reduction depended on the metabolic pathway triggered by a given substrate.

Fluorescence Spectroscopy Analysis of the Bacteria-Mineral Interface: Adsorption of Lipopolysaccharides to Silica and Alumina

We present here a quantification of the sorption process and molecular conformation involved in the attachment of bacterial cell wall lipopolysaccharides (LPSs), extracted from Escherichia coli, to silica (SiO₂) and alumina (Al₂O₃) particles. We propose that interfacial forces govern the physicochemical interactions of the bacterial cell wall with minerals in the natural environment, and the molecular conformation of LPS cell wall components depends on both the local charge at the point of binding and hydrogen bonding potential. This has an effect on bacterial adaptation to the host environment through adhesion, growth, function, and ability to form biofilms. Photophysical techniques were used to investigate adsorption of fluorescently labeled LPS onto mineral surfaces as model systems for bacterial attachment. Adsorption of macromolecules in dilute solutions was studied as a function of pH and ionic strength in the presence of alumina and silica via fluorescence, potentiometric, and mass spectrometry techniques. The effect of silica and alumina particles on bacterial growth as a function of pH was also investigated using spectrophotometry. The alumina and silica particles were used to mimic active sites on the surface of clay and soil particles, which serve as a point of attachment of bacteria in natural systems. It was found that LPS had a high adsorption affinity for Al₂O₃ while adsorbing weakly to SiO₂ surfaces. Strong adsorption was observed at low pH for both minerals and varied with both pH and mineral concentration, likely in part due to conformational rearrangement of the LPS macromolecules. Bacterial growth was also enhanced in the presence of the particles at low pH values. This demonstrates that at a molecular level, bacterial cell wall components are able to adapt their conformation, depending on the solution pH, in order to maximize attachment to substrates and guarantee community survival.

Thorn-like TiO2 nanoarrays with broad spectrum antimicrobial activity through physical puncture and photocatalytic action

To overcome the conventional limitation of TiO2 disinfection being ineffective under light-free conditions, TiO2 nanowire films (TNWs) were prepared and applied to bacterial disinfection under dark and UV illumination. TNW exhibited much higher antibacterial efficiencies against Escherichia coli (E. coli) under dark and UV illumination conditions compared to TiO2 nanoparticle film (TNP) which was almost inactive in the dark, highlighting the additional contribution of the physical interaction between bacterial membrane and NWs. Such a physical contact-based antibacterial activity was related to the NW geometry such as diameter, length, and density. The combined role of physical puncture and photocatalytic action in the mechanism underlying higher bactericidal effect of TNW was systematically examined by TEM, SEM, FTIR, XPS, and potassium ion release analyses. Moreover, TNW revealed antimicrobial activities in a broad spectrum of microorganisms including Staphylococcus aureus and MS2 bacteriophage, antibiofilm properties, and good material stability. Overall, we expect that the free-standing and antimicrobial TNW is a promising agent for water disinfection and biomedical applications in the dark and/or UV illumination.

The Pseudomonas aeruginosa biofilm matrix and cells are drastically impacted by gas discharge plasma treatment: A comprehensive model explaining plasma-mediated biofilm eradication

Biofilms are microbial communities encased in a protective matrix composed of exopolymeric substances including exopolysaccharides, proteins, lipids, and extracellular DNA. Biofilms cause undesirable effects such as biofouling, equipment damage, prostheses colonization, and disease. Biofilms are also more resilient than free-living cells to regular decontamination methods and therefore, alternative methods are needed to eradicate them. The use of non-thermal atmospheric pressure plasmas is a good alternative as plasmas contain reactive species, free radicals, and UV photons well-known for their decontamination potential against free microorganisms. Pseudomonas aeruginosa biofilms colonize catheters, indwelling devices, and prostheses. Plasma effects on cell viability have been previously documented for P. aeruginosa biofilms. Nonetheless, the effect of plasma on the biofilm matrix has received less attention and there is little evidence regarding the changes the matrix undergoes. The aim of this work was to study the effect plasma exerts mostly on the P. aeruginosa biofilm matrix and to expand the existing knowledge about its effect on sessile cells in order to achieve a better understanding of the mechanism/s underlying plasma-mediated biofilm inactivation. We report a reduction in the amount of the biofilm matrix, the loss of its tridimensional structure, and morphological changes in sessile cells at long exposure times. We show chemical and structural changes on the biofilm matrix (mostly on carbohydrates and eDNA) and cells (mostly on proteins and lipids) that are more profound with longer plasma exposure times. We also demonstrate the presence of lipid oxidation products confirming cell membrane lipid peroxidation as plasma exposure time increases. To our knowledge this is the first report providing detailed evidence of the variety of chemical and structural changes that occur mostly on the biofilm matrix and sessile cells as a consequence of the plasma treatment. Based on our results, we propose a comprehensive model explaining plasma-mediated biofilm inactivation.

Arsenite and arsenate binding to ferrihydrite organo-mineral coprecipitate: Implications for arsenic mobility and fate in natural environments

Arsenic mobility in soils, sediments and groundwater systems is strongly controlled by adsorption occurring at iron oxide/water interfaces, and the extent of this adsorption may be influenced by the presence of natural organic matter (NOM). This study aims to investigate the adsorption of As(III) and As(V) onto coprecipitates made with ferrihydrite (Fh) and humic acid (HA) with two organic carbon (OC) loadings of 5 and 15 wt% OC. We show that the coprecipitation of HA with Fh can significantly reduce the retention of both As(III) and As(V) over a wide pH range (4-11), and with increased OC loading, there is reduced arsenic adsorption. On pure Fh, As(III) is adsorbed to a greater extent than As(V) at pH > 6.5 (the crossover pH), whereas the crossover pH shifts to more acidic pH in the presence of HA, implying that the binding of As(III) is more favorable than As(V) in the presence of NOM. Both As(III) and As(V) are complexed with the ferric hydroxyl functional groups, and no ternary Fh-HA-As complexes are detected. We observe that ∼40% of the adsorbed As(III) is oxidized to As(V) on pure Fh, compared to only ∼29% of As(III) oxidation on the Fh-HA coprecipitate, indicating that NOM hinders As(III) oxidation on iron (hydr)oxide. The results of this study suggest that NOM interacts with arsenic in ways that promote arsenic mobility and especially promote the mobility of arsenate relative to arsenite, which is of great significance for evaluating the migration and bioavailability of arsenic in both natural and contaminated environments.

Extracellular electron transfer of Enterobacter cloacae SgZ-5T via bi-mediators for the biorecovery of palladium as nanorods

In nature, microbes use extracellular electron transfer (EET) to recover noble metals. Most attention has been paid to the biorecovery process occurring intracellularly and on the cell surface. In this work, we report that Pd nanorods could be biosynthesized by Enterobacter cloacae SgZ-5T in the extracellular space. This bacterium possesses both a direct EET pathway through membrane redox systems and an indirect EET pathway via the self-secreted electron carrier hydroquinone (HQ). When exposed to Pd(II), the bacteria adjusted their metabolic pathway and membrane-bound proteins to secrete riboflavin (RF). However, no HQ was detected in the supernatant in presence of Pd(II). No significant change was observed through metabolomic analysis regarding the abundance of HQ in presence of Pd(II) compared to Pd(II)-free supernatant. Similar results were also obtained through transcriptomic analysis of YqjG gene encoding glutathionyl-HQ reductase synthase. X-ray photoelectron spectroscopic evidence indicated that HQ may adsorb to the surface of Pd nanorods. Moreover, the gene encoding RF synthase (ribE) was up-regulated in the present of Pd(II), suggesting that this bioreduction process induced RF synthase, which had been shown in previous results. The UV-vis spectroscopy data demonstrated that the Pd(II) reduction rate was enhanced by 5%, 5.5% and 30% by the addition of 3.33 μM HQ, 3.33 μM RF and the both, respectively. All these results revealed that the bi-mediators secreted by bacteria were beneficial for biorecovery of Pd. This work is of significance for understanding metal biorecovery processes and natural biogeochemical processes.