Surface-Nanoengineered Bacteria for Efficient Local Enrichment and Biodegradation of Aqueous Organic Wastes: Using Phenol as a Model Compound

Cancer phototherapy with nano-bacteria biohybrids

The utilization of light for therapeutic interventions, also known as phototherapy, has been extensively employed in the treatment of a wide range of illnesses, including cancer. Despite the benefits of its non-invasive nature, phototherapy still faces challenges pertaining to the delivery of phototherapeutic agents, phototoxicity, and light delivery. The incorporation of nanomaterials and bacteria in phototherapy has emerged as a promising approach that leverages the unique properties of each component. The resulting nano-bacteria biohybrids exhibit enhanced therapeutic efficacy when compared to either component individually. In this review, we summarize and discuss the various strategies for assembling nano-bacteria biohybrids and their applications in phototherapy. We provide a comprehensive overview of the properties and functionalities of nanomaterials and cells in the biohybrids. Notably, we highlight the roles of bacteria beyond their function as drug vehicles, particularly their capacity to produce bioactive molecules. Despite being in its early stage, the integration of photoelectric nanomaterials and genetically engineered bacteria holds promise as an effective biosystem for antitumor phototherapy. The utilization of nano-bacteria biohybrids in phototherapy is a promising avenue for future investigation, with the potential to enhance treatment outcomes for cancer patients.

Chemical Approaches for the Preparation of Bacteria - Nano/Microparticle Hybrid Systems

Bacteria represent a class of living cells that are very attractive carriers for the transport and delivery of nano- and microsized particles. The use of cell-based carriers, such as for example bacteria, may allow to precisely direct nano- or microsized cargo to a desired site, which would greatly enhance the selectivity of drug delivery and allow to mitigate side effects. One key step towards the use of such nano-/microparticle - bacteria hybrids is the immobilization of the cargo on the bacterial cell surface. To fabricate bacteria - nano-/microparticle biohybrid microsystems, a wide range of chemical approaches are available that can be used to immobilize the particle payload on the bacterial cell surface. This article presents an overview of the various covalent and noncovalent chemistries that are available for the preparation of bacteria - nano-/microparticle hybrids. For each of the different chemical approaches, an overview will be presented that lists the bacterial strains that have been modified, the type and size of nanoparticles that have been immobilized, as well as the methods that have been used to characterize the nanoparticle-modified bacteria.

A novel combination of immobilized Enterococcus casseliflavus sp. nov. with silver nanoparticles into a reusable matrix of Ca-Alg beads as a new strategy for biotreatment of Disperse Blue 183: Insights into metabolic characterization, biotoxicity, and mutagenic properties

Recent advances in immobilized biologic systems for decolorizing azo dyes are gaining great attention due to microorganisms like bacteria and nanoparticles that could stimulate decolorization. Enhanced decolorization performance was observed in this study, indicating the great potential of the immobilized complex of bacterial cells and AgNPs as an alternative to the traditional biological processes to improve the performance of biological systems. The biodegradation and decolorization of Disperse Blue183 (DB 183) were investigated utilizing a novel combination of Enterococcus casseliflavus strain A₂ mediated by silver nanoparticles synthesized by Marinospirillum alkaliphilum strain N in three different conditions. Ⅰ: free bacterial strain A₂ (100% dye removal in 72 h), Ⅱ: immobilized bacterial strain A₂ in Ca-Alg beads (100% dye removal in 15 h), and Ⅲ: immobilized bacterial strain A₂ with silver nanoparticles (AgNPs) as support in Ca-Alg beads (100% dye removal in 9 h). The presence of bacterial cells and nanoparticles in Ca-Alg beads was assessed and proved by scanning electron microscope (SEM) and X-ray energy diffraction (EDX) analysis. Moreover, DB 183 and its decolorization metabolites were evaluated by applying UV-Vis, infrared spectroscopy (FTIR), and GC/MS, and the results showed that the dye was degraded. The antimicrobial effect, brine shrimp toxicity (BST) test, and mutagenicity assay in the presence and absence of metabolic activation (+S9/-S9) were run to assess DB 183 and metabolite obtained from biodegradation. The antimicrobial activity of DB 183 disappeared after treatment. Further, the results of the BST test determined that the dye has moderate biotoxicity (LC₅₀:0.064 mg/mL), and the after-treatment product was not toxic. According to the Ames test, DB 183 had mutagenicity effect (69-84%), and the metabolic activation increased the mutagenicity of the dye) 12-25%). However, the percentage mutagenicity of decolorization products decreased, ranging from 50 to 80% without activation (-S9) and 83-96% in present activation (+S9). This work used the immobilized bacterial cells and AgNPs Ca-Alg gel beads for the first time to introduce this kind of system as a suitable technique for rapid decolorization. Using this application enables a remarkable reduction in the time dedicated to the bioremediation of dyeing wastewater.

A comprehensive review on removal of pollutants from wastewater through microbial nanobiotechnology -based solutions

Increasing wastewater pollution owing to the briskly rising human population, rapid industrialization, and fast urbanization has necessitated highly efficient wastewater treatment technologies. Although several methods of wastewater treatments are in practice, expensiveness, use of noxious chemicals, generation of unsafe by-products, and longer time consumption restrain their use to a great extent. Over the last few decades, nanotechnological wastewater treatment approaches have received widespread recognition globally. Microbially fabricated nanoparticles reduce the utilization of reducing, capping, and stabilizing agents, and exhibit higher adsorptive and catalytic efficiency than chemically synthesized nanomaterials. The present review comprehensively summarizes the applications of microbial nanotechnology in the removal of a wide range of noxious wastewater pollutants. Moreover, prospects and challenges associated with the integration of nanotechnology with other biological treatment technologies including algal-membrane bioreactor, aerobic digestion, microbial fuel cells, and microbial nanofiber webs have also been briefly discussed.

Characterization of Immobilized Magnetic Fe3O4 Nanoparticles on Raoultella Ornithinolytica sp. and Its Application for Azo Dye Removal

A high-performance immobilized bacterial strain coated with magnetic iron oxide nanoparticles was used for Basic Blue 41 azo dye (BB 41 dye) decolorization. To create the coated bacterial strain, Raoultella Ornithinolytica sp. was isolated and identified under the accession number KT213695, then coated with manufactured magnetic iron oxide nanoparticles. SEM and SEM-EDX were used to characterize the coated bacteria and validate its morphological structure formation. The coated Raoultella Ornithinolytica sp. A1 (coated A1) generated a 95.20% decolorization for BB 41 dye at 1600 ppm starting concentration with an optimal dose of coated A1 5 mL/L, pH 8, under static conditions for 24 h at 37 °C. Continuous batch cycles were used, with BB 41 dye (1600 ppm) added every 24 h four times, to achieve a high decolorization efficiency of 80.14%. Furthermore, the metabolites of BB 41 dye biodegradation were investigated by gas chromatographic-mass spectrum analysis (GC-MS) and showed a less toxic effect on the bioindicator Artemia salina. Additionally, 5 mL/L of coated A1 demonstrated the highest decolorization rate (47.2%) when applied to a real wastewater sample after 96 h with a consequent reduction in COD from 592 to 494 ppm.

A smart enzyme reactor based on a photo-responsive hydrogel for purifying water from phenol contaminated sources

In this paper, a smart enzyme reactor (SER) was synthesized using immobilized tyrosinase (Tyr) in a photo-responsive hydrogel via a polydopamine-assisted self-assembly strategy for purifying water from phenol contaminated water. PDA was not only utilized as a binder between Tyr and the hydrogel to prevent the leakage of Tyr with relatively high enzymatic activity from the SER, but also acted as a light absorber to trigger the hydrophilic/hydrophobic switching of PNIPAm hydrogels to realize the efficient reclamation of clean water. Experimental results showed that the SER maintained a well-defined porous structure with excellent elasticity, which was beneficial for water transport and enzyme accessibility. And the stability and reusability of Tyr in the degradation of phenol were all improved. Furthermore, clean water could be reclaimed completely and facilely by light irradiation after enzymatic remediation in the SER.

3D Printed Bioresponsive Devices with Selective Permeability Inspired by Eggshell Membrane for Effective Biochemical Conversion

Eggshell membrane has selective permeability that enables gas or liquid molecules to pass through while effectively preventing migration of microbial species. Herein, inspired by the architecture of the eggshell membrane, we employ three-dimensional (3D) printing techniques to realize bioresponsive devices with excellent selective permeability for effective biochemical conversion. The fabricated devices show 3D conductive carbon nanofiber membranes in which precultured microbial cells are controllably deployed. The resulting outcome provides excellent selective permeability between chemical and biological species, which enables acquisition of target responses generated by biological species confined within the device upon input signals. In addition, electrically conductive carbon nanofiber networks provide a platform for real-time monitoring of metabolism of microbial cells in the device. The suggested platform represents an effort to broaden microbial applications by constructing biologically programmed devices for desired responses enabled by designated deployment of engineered cells in a securely confined manner within enclosed membranes using 3D printing methods.

Removal of phenol from aqueous solution using acid-modified Pseudomonas putida-sepiolite/ZIF-8 bio-nanocomposites

The discharge of phenol, a harmful pollutant, in the environment poses a threat to human health. With the rapid urbanization and industrialization of the land, there is a pressing need to find new technologies and efficient adsorption materials to address phenol contamination. As a potential adsorbent candidate, sepiolite (SEP) has garnered much interest owing to its large specific surface area, and excellent adsorption performance and biocompatibility. Herein, nanocomposite CESEP/ZIF-8, consisting of zeolite imidazole framework (ZIF-8) and hydrochloric acid-modified SEP (CESEP), was prepared and examined toward the adsorption of phenol. Adsorption equilibrium was achieved within 150 min at initial phenol solution concentrations of 10 and 20 mg/L. However, complete removal was not achieved. Accordingly, biodegradation was introduced. Microorganism Pseudomonas putida was immobilized onto CESEP/ZIF-8, which afforded synergistic adsorption and biodegradation action. Phenol at solution concentrations of 10 and 20 mg/L was effectively removed within 13 and 24 h, respectively (as opposed to 21 and 36 h when phenol was removed in the presence of free Pseudomonas putida solely). The synergistic physical-biological treatment presented herein is expected to have great potential in the field of wastewater treatment.

Immobilization of functional nano-objects in living engineered bacterial biofilms for catalytic applications

Nanoscale objects feature very large surface-area-to-volume ratios and are now understood as powerful tools for catalysis, but their nature as nanomaterials brings challenges including toxicity and nanomaterial pollution. Immobilization is considered a feasible strategy for addressing these limitations. Here, as a proof-of-concept for the immobilization of nanoscale catalysts in the extracellular matrix of bacterial biofilms, we genetically engineered amyloid monomers of the Escherichia coli curli nanofiber system that are secreted and can self-assemble and anchor nano-objects in a spatially precise manner. We demonstrated three scalable, tunable and reusable catalysis systems: biofilm-anchored gold nanoparticles to reduce nitro aromatic compounds such as the pollutant p-nitrophenol, biofilm-anchored hybrid Cd_0.9Zn_0.1S quantum dots and gold nanoparticles to degrade organic dyes and biofilm-anchored CdSeS@ZnS quantum dots in a semi-artificial photosynthesis system for hydrogen production. Our work demonstrates how the ability of biofilms to grow in scalable and complex spatial arrangements can be exploited for catalytic applications and clearly illustrates the design utility of segregating high-energy nano-objects from injury-prone cellular components by engineering anchoring points in an extracellular matrix.

Novel mesoporous organosilica nanoparticles with ferrocene group for efficient removal of contaminants from wastewater

Traditional method to functionalize mesoporous silica nanoparticles with organic groups for removal of contaminants from wastewater was surface modification. However, this surface modification could not cover the entire surface, leading to incomplete utilization of the high surface area of MSNs. In this work, we designed and prepared a novel inorganic-organic hybrid nanomaterial: ferrocene incorporated mesoporous organosilica nanoparticles (MONs). Owing to the mesoporous structure, large surface area and the ferrocene group in the framework, MONs could adsorb phosphate anion more efficiently with adsorption capacities up to 1299 mg/g than surface modified MSNs (SiO₂-Fe) (488 mg/g). Congo red (CR) and Pb²⁺ were also used as the model contaminants, and the results indicated that MONs is a superior absorbent comparing with ferrocene surface modified MSNs.

Adsorption and biodegradation of dye in wastewater with Fe3O4@MIL-100 (Fe) core-shell bio-nanocomposites

Adsorption and improved biodegradation of dyes in wastewater was achieved with Fe₃O₄@MIL-100 core-shell bio-nanocomposites, which were prepared by a step-by-step strategy and attached to the surface of bacteria via zero-length carbodiimide chemistry. The Fe₃O₄@MIL-100 (Fe) nano-composite showed excellent dye adsorption properties and the overall dye removal process followed second-order kinetics. The dye AO10 was completely eliminated from solution by the combined effects of adsorption and biodegradation within 15 and 25 h from initial dye concentrations of 25 and 50 mg/L, respectively. The time to degrade the dye decreased from 11 h for the free microorganisms to 5 h for the bio-nanocomposite. The procedure was non-toxic, allowed for magnetic separation of the bio-nanocomposite from solution, and showed good cycling performance for the removal of dye. Hence, the strategy of surface-engineering bacteria shows great potential for the treatment of dyes from industrial effluents.

Remediation of water contaminated with diesel oil using a coupled process: Biological degradation followed by heterogeneous Fenton-like oxidation

The treatment of a synthetically prepared wastewater containing diesel oil has been investigated using combined treatment schemes based on the biological treatment followed by an advanced oxidation process. 78% of diesel oil was degraded by Acinetobacter venetianus in 96 h, while the removal efficiency of chemical oxygen demand (COD) in the aqueous phase was only 56.8%, indicating that degraded metabolites existed in solution. To solve this problem, a Fenton-like system consisting of nanoscale zero-valent iron (nZVI) and hydrogen peroxide was used for further oxidation of the metabolites after biodegradation. Results showed that the total COD removal increased from 56.8% to 89% under the optimal condition. In addition, effects of initial pH (2.0-9.0), ZVI dosage (0-2.0 g L-1), hydrogen peroxide (H₂O₂) dosage concentration (0-15 mmol L-1) and temperature (298-308 K) on the treatment efficiency of the combined process were studied. Scanning electron microscopy (SEM) demonstrated that changes to the surface of nZVI occurred. GC-MS revealed that the degraded metabolites were mineralized practically by nZVI/H₂O₂ system. The results points towards the potential of Fenton-like oxidation as a short post-treatment after a biological process for the treatment of organic pollutants in wastewater.

Bioaugmentation: An Emerging Strategy of Industrial Wastewater Treatment for Reuse and Discharge

A promising long-term and sustainable solution to the growing scarcity of water worldwide is to recycle and reuse wastewater. In wastewater treatment plants, the biodegradation of contaminants or pollutants by harnessing microorganisms present in activated sludge is one of the most important strategies to remove organic contaminants from wastewater. However, this approach has limitations because many pollutants are not efficiently eliminated. To counterbalance the limitations, bioaugmentation has been developed and consists of adding specific and efficient pollutant-biodegrading microorganisms into a microbial community in an effort to enhance the ability of this microbial community to biodegrade contaminants. This approach has been tested for wastewater cleaning with encouraging results, but failure has also been reported, especially during scale-up. In this review, work on the bioaugmentation in the context of removal of important pollutants from industrial wastewater is summarized, with an emphasis on recalcitrant compounds, and strategies that can be used to improve the efficiency of bioaugmentation are also discussed. This review also initiates a discussion regarding new research areas, such as nanotechnology and quorum sensing, that should be investigated to improve the efficiency of wastewater bioaugmentation.