Proposed mechanisms of electron uptake in metal-corroding methanogens and their potential for CO2 bioconversion applications.

Some methanogens are electrotrophic bio-corroding microbes that can acquire electrons from solid surfaces including metals. In the laboratory, pure cultures of methanogenic cells oxidize iron-based materials including carbon steel, stainless steel, and Fe0. For buried or immersed pipelines or other metallic structures, methanogens are often major components of corroding biofilms with complex interspecies relationships. Models explaining how these microbes acquire electrons from solid donors are multifaceted and include electron transfer via redox mediators such as H2 or by direct contact through membrane proteins. Understanding the electron uptake (EU) routes employed by corroding methanogens is essential to develop efficient strategies for corrosion prevention. It is also beneficial for the development of bioenergy applications relying on methanogenic EU from solid donors such as bioelectromethanogenesis, hybrid photosynthesis, and the acceleration of anaerobic digestion with electroconductive particles. Many methanogenic species carrying out biocorrosion are the same ones forming the extensive abiotic-biological interfaces at the core of these bio-applications. This review will discuss the interactions between corrosive methanogens and metals and how the EU capability of these microbes can be harnessed for different sustainable biotechnologies.

Ultrafast removal of toxic Cr(VI) by the marine bacterium Vibrio natriegens.

The fastest-growing microbe Vibrio natriegens is an excellent platform for bioproduction processes. Until now, this marine bacterium has not been examined for bioremediation applications, where the production of substantial amounts of biomass would be beneficial. V. natriegens can perform extracellular electron transfer (EET) to Fe(III) via a single porin-cytochrome circuit conserved in Vibrionaceae. Electroactive microbes capable of EET to Fe(III) usually also reduce toxic metals such as carcinogenic Cr(VI), which is converted to Cr(III), thus decreasing its toxicity and mobility. Here, the performance of V. natriegens was explored for the bioremediation of Cr(VI). At a density of 100 mg/mL, V. natriegens removed 5-20 mg/L Cr(VI) within 30 s and 100 mg/L Cr(VI) within 10 min. In comparison, the model bacterium Escherichia coli grown to a comparable cell density removed Cr(VI) 36 times slower. To eliminate Cr(VI), V. natriegens had to be metabolically active, and functional outer-membrane c-type cytochromes were required. At the end of the Cr(VI) removal process, V. natriegens had reduced all of it into Cr(III) while adsorbing more than half of the metallic ions. These results demonstrate that V. natriegens, with its fast metabolism, is a viable option for the rapid treatment of aqueous pollution with Cr.

An Electroconductive and Antibacterial Adhesive Nanocomposite Hydrogel for High-Performance Skin Wound Healing.

Multifunctional hydrogel adhesives inhibiting infections and enabling the electrical stimulation (ES) of tissue reparation are highly desirable for the healing of surgical wounds and other skin injuries. Herein, a therapeutic nanocomposite hydrogel is designed by integrating ß-cyclodextrin-embedded Ag nanoparticles (CDAgNPs) in a polyvinyl alcohol (PVA) matrix enhanced with free ß-cyclodextrin (CD) and an atypical macromolecule made of ß-glucan grafted with hyaluronic acid (HAG). The main objective is to develop a biocompatible dressing combining the electroconductivity and antibacterial activity of CDAgNPs with the cohesiveness and porosity of PVA and the anti-inflammatory, moisturizing, and cell proliferation-promoting properties of HAG. The last component, CD, is added to strengthen the network structure of the hydrogel. PVA/CD/HAG/CDAgNP exhibited excellent adhesion strength, biocompatibility, electroconductivity, and antimicrobial activity against a wide range of bacteria. In addition, the nanocomposite hydrogel has a swelling ratio and water retention capacity suitable to serve as a wound dressing. PVA/CD/HAG/CDAgNP promoted the proliferation of fibroblast in vitro, accelerated the healing of skin wounds in an animal model, and is hemostatic. Upon ES, the PVA/CD/HAG/CDAgNP nanocomposite hydrogel became more efficient both in vitro and in vivo further speeding up the skin healing process thus demonstrating its potential as a next-generation electroconductive wound dressing.

Genetic tools for the electrotroph Sporomusa ovata and autotrophic biosynthesis.

Sporomusa ovata is a Gram-negative acetogen of the Sporomusaceae family with a unique physiology. This anerobic bacterium is a core microbial catalyst for advanced CO2-based biotechnologies including gas fermentation, microbial electrosynthesis, and hybrid photosystem. Until now, no genetic tools exist for S. ovata, which is a critical obstacle to its optimization as an autotrophic chassis and the acquisition of knowledge about its metabolic capacities. Here, we developed an electroporation protocol for S. ovata. With this procedure, it became possible to introduce replicative plasmids such as pJIR751 and its derivatives into the acetogen. This system was then employed to demonstrate the feasibility of heterologous expression by introducing a functional ß-glucuronidase enzyme under the promoters of different strengths in S. ovata. Next, a recombinant S. ovata strain producing the non-native product acetone both from an organic carbon substrate and from CO2 was constructed. Finally, a replicative plasmid capable of integrating itself on the chromosome of the acetogen was developed as a tool for genome editing, and gene deletion was demonstrated. These results indicate that S. ovata can be engineered and provides a first-generation genetic toolbox for the optimization of this biotechnological workhorse.IMPORTANCES. ovata harbors unique features that make it outperform most microbes for autotrophic biotechnologies such as a capacity to acquire electrons from different solid donors, a low H2 threshold, and efficient energy conservation mechanisms. The development of the first-generation genetic instruments described in this study is a key step toward understanding the molecular mechanisms involved in these outstanding metabolic and physiological characteristics. In addition, these tools enable the construction of recombinant S. ovata strains that can synthesize a wider range of products in an efficient manner.

Electrochemiluminescent CdS Quantum Dots Biosensor for Cancer Mutation Detection at Different Positions on Linear DNA Analytes.

PCR-based techniques routinely employed for the detection of mutated linear DNA molecules, including circulating tumor DNA (ctDNA), require large nucleotide sections on both sides of the mutation for primer annealing. This means that DNA fragments with a mutation positioned closer to the extremities are unlikely to be detected. Thus, sensors capable of recognizing linear DNA with characteristic mutations closer to the ends would be advantageous over the state-of-the-art approaches. Here, an electrochemiluminescence-resonance energy transfer (ECL-RET) biosensor comprising capped CdS quantum dots and hairpin DNA probes labeled with Au nanoparticles was developed for the detection of epidermal growth factor receptor (EGFR) ctDNA carrying the critical T790M lung cancer mutation. The ECL-RET system detected different DNA molecules including single-stranded 18-nucleotides (nt) and 40-nt as well as double-stranded 100-nt with the single nucleotide polymorphism (SNP) coding for T790M located either in the middle or only 7 nt from one end. For all target DNA, the sensor's limits of detection (LODs) were in the aM range, with excellent selectivity. It was the case of 100-nt target linear ctDNA fragments with LODs of 8.1 and 3.4 aM when the EGFR T790M SNP was either in the middle or at the end, respectively. These results show that ECL-RET systems can sense mutations in DNA fragments that would remain undetected by standard techniques.

Versatile iodine-doped BiOCl with abundant oxygen vacancies and (110) crystal planes for enhanced pollutant photodegradation.

Crystal plane regulation, defect engineering, and element doping can effectively solve the problems of large band gaps, poor light absorption, and fast recombination of BiOCl. In this work, iodine-doped BiOCl (I/BiOCl) nanowafers with abundant (110) crystal planes and oxygen vacancies (OV) were prepared by a simple hydrothermal method and assessed for pollutant photodegradation. I/BiOCl with a molar ratio of I to Cl of 0.6 (I0.6/BiOCl) degraded under visible light 95.8% of the toxic dye rhodamine B and 85.1% of the persistent antibiotic tetracycline in 5 and 10 min, respectively. In comparison, unmodified BiOCl photodegraded only between 42.0% and 48.2% of these critical water pollutants. Furthermore, I0.6/BiOCl was highly stable with most of its photocatalytic activity remaining after 4 cycles. Three reasons explain the excellent photodegradation properties of I0.6/BiOCl. First, the doped photocatalyst grew abundant (110) crystal planes, which inhibits the recombination of photogenerated electron-hole pairs. Second, the large quantity of OV present in I0.6/BiOCl increased active sites for reactive oxygen species generation, improved photogenerated charge separation, and pollutants adsorption. Lastly, I0.6/BiOCl had a modified electronic band structure enhancing light absorption. Overall, these results describe a promising photocatalyst capable of degrading efficiently major pollutants with different structures.

Bacterial cellulose flakes loaded with Bi2MoO6 nanoparticles and quantum dots for the photodegradation of antibiotic and dye pollutants.

Effective strategies to improve charge separation in semiconductor particles are critical for improving the photodegradation of organic pollutants at levels sufficient for environmental applications. Herein, Bi2MoO6 (BMOMOF), comprising both nanoparticles (NPs) and quantum dots (QDs), was synthesized from a bismuth-based metal-organic framework (Bi-MOF) precursor. Surface defects on BMOMOF, the combination of NPs and QDs, and modified energy band edges improved photogenerated charge separation and facilitated redox reactions. When compared to BMO derived from uncoordinated Bi, the BMOMOF photocatalyst (PC) was more efficient at photodegrading tetracycline hydrochloride (TCH) and ciprofloxacin (CIP), two widely-used antibiotics ubiquitous in wastewater, as well as the carcinogenic pollutant rhodamine B (RhB). BMOMOF was then loaded on the biopolymer bacterial cellulose (BC) to further enhance photocatalytic performance and facilitate the recovery of the PC after water treatment processes. The novel BMOMOF/BC photocatalytic flakes were significantly larger than pure BMOMOF, and thus easier to recuperate. Furthermore, anchoring BMOMOF on BC flakes augmented significantly the photodegradation of TCH, CIP, and RhB, mainly because hydroxyl groups in BC act as hole traps facilitating photogenerated electron-hole separation. Results obtained with BMOMOF/BC highlight promising approaches to develop optimal PCs for aqueous pollutants degradation.

Electrostimulation of fibroblast proliferation by an electrospun poly (lactide-co-glycolide)/polydopamine/chitosan membrane in a humid environment.

Exogenous electrical stimulation (ES) facilitates skin wound healing and accelerates cell proliferation. Scaffolds fabricated with electrically-conductive materials combined with ES further promote cellular activity. Here, an electrospun membrane made of poly (lactide-co-glycolide) (PLGA) coated with chitosan (CS) via polydopamine (PDA) serving as a linker was developed and evaluated in vitro for the proliferation and migration of fibroblast cells involved in skin wound repair. PLGA/PDA/CS exhibited multiple optimal characteristics for cell proliferation and dressing materials including good mechanical properties, low cytotoxicity, a super-hydrophilic surface, and an excellent swelling ratio suitable for the absorption of wound exudates. Because of ionic charges, wet PLGA/PDA/CS had an electrical conductivity of 2.85 × 10-3 S/cm, which was comparable to the highest electrical conductivities observed with natural skin. Upon intermittent ES of 100 mV, PLGA/PDA/CS increased fibroblast proliferation 2 and 1.3 times compared to PLGA and PLGA/PDA, respectively. These results demonstrate the potential of PLGA/PDA/CS as a biodegradable polymeric surface for the ES of cells involved in skin wound healing. It also shows that polymers with low electrical conductivity in dry conditions can become suitable for the ES of humid wounds where ionic conductivity is occurring.

Fast-growing cyanobacteria bio-embedded into bacterial cellulose for toxic metal bioremediation.

Cyanobacterial biomass and cellulose-based materials have been used separately as green bio-adsorbents for the removal of toxic metals from water. Hybrid materials made of living microbial cells encased in a solid matrix have shown good potential for bioremediation. Here, the fast-growing cyanobacterium Synechococcus elongatus UTEX 2973 was embedded in situ into bacterial cellulose (BC), a robust biopolymer rich in hydroxyl groups with excellent water holding capacity. The living material was obtained by injecting S. elongatus into a Komagataeibacter sucrofermentans culture producing BC. Several types of BC/S. elongatus (BC/SE) materials were developed including small spheroids and flat films with different cyanobacteria loads via simple adjustments of the biosynthesis process parameters. BC/SE spheroids were evaluated for toxic copper removal and exhibited excellent adsorption properties compared to pure BC with a maximum capacity of 156.25 mg g-1. Thus, this simple bio-embedding approach holds promises in the development of living materials for environmental applications.

A two-stage process for the autotrophic and mixotrophic conversion of C1 gases into bacterial cellulose.

Gas fermentation is a well-established process for the conversion of greenhouse gases from industrial wastes into valuable multi-carbon chemicals. Here, a two-stage process was developed to expand the product range of gas fermentation and synthesized the versatile biopolymer bacterial cellulose (BC). In the first stage, the acetogen Clostridium autoethanogenum was cultivated with H2:CO:CO2 and produced ethanol and acetate. In the second stage, BC-synthesizing Komagataeibacter sucrofermentans was grown in the spent medium from gas fermentation. K. sucrofermentans was able to produce BC autotrophically from gas-derived metabolites alone as well as mixotrophically with the addition of exogenous glucose. In these circumstances, 1.31 g/L BC was synthesized with a major energetic contribution from C1 gas fermentation products. Mixotrophic BC characterization reveals unique properties including augmented mechanical strength, porosity, and crystallinity. This proof-of-concept process demonstrates that BC can be produced from gases and holds good potential for the efficient conversion of C1 wastes.

Fumarate disproportionation by Geobacter sulfurreducens and its involvement in biocorrosion and interspecies electron transfer.

The model electroactive bacterium Geobacter sulfurreducens can acquire electrons directly from solid donors including metals and other species. Reports on this physiology concluding that solid donors are the only electron sources were conducted with fumarate believed to serve exclusively as the terminal electron acceptor (TEA). Here, G. sulfurreducens was repeatedly transferred for adaptation within a growth medium containing only fumarate and no other solid or soluble substrate. The resulting evolved strain grew efficiently with either the C4-dicarboxylate fumarate or malate acting simultaneously as electron donor, carbon source, and electron acceptor via disproportionation. Whole-genome sequencing identified 38 mutations including one in the regulator PilR known to repress the expression of the C4-dicarboxylate antiporter DcuB essential to G. sulfurreducens when growing with fumarate. Futhermore, the PilR mutation was identical to the sole mutation previously reported in an evolved G. sulfurreducens grown in a co-culture assumed to derive energy solely from direct interspecies electron transfer, but cultivated with fumarate as the TEA. When cultivating the fumarate-adapted strain in the presence of stainless steel and fumarate, biocorrosion was observed and bacterial growth was accelerated 2.3 times. These results suggest that G. sulfurreducens can conserve energy concomitantly from C4-dicarboxylate disproportionation and the oxidation of a solid electron donor. This co-metabolic capacity confers an advantage to Geobacter for survival and colonization and explains in part why these microbes are omnipresent in different anaerobic ecosystems.

Improved polyhydroxybutyrate production by Cupriavidus necator and the photocatalyst graphitic carbon nitride from fructose under low light intensity.

The photocatalyst graphitic carbon nitride (g-C3N4) is known to photostimulate the production of the bioplastic polyhydroxybutyrate (PHB) by Cupriavidus necator. In previous studies, the combination of C. necator and g-C3N4 increased PHB yield from either an organic or inorganic carbon substrate under a light intensity of 4200 lx. Here, different parameters including light intensity, pH, temperature, nitrogen and carbon concentrations, aeration, and inoculum size were explored to maximize PHB production by hybrid photosynthesis from fructose and visible light. A g-C3N4/C. necator culture grown with a lower light intensity of 2100 lx, an inoculum size of 128.30 × 106 CFU ml-1, and constant aeration produced 7.16 g l-1 d-1 PHB with a product yield from fructose of 60.94%. Furthermore, the ratio of incident photons harvested by g-C3N4 converted into NADPH+H+ by C. necator for PHB production was improved to 19.74% after the process optimization. In comparison, the PHB production rate of a non-optimized g-C3N4/C. necator system exposed to 4200 lx was only 2.94 g l-1 d-1 with a product yield from fructose of 33.29%. These results demonstrate that hybrid photosynthesis productivity can be significantly augmented by decreasing light intensity and adjusting other parameters, which is promising for future bioproduction applications.

An electrochemiluminescence resonance energy transfer biosensor for the detection of circulating tumor DNA from blood plasma.

A liquid biopsy is a noninvasive approach for detecting double-stranded circulating tumor DNA (ctDNA) of 90-320 nucleotides in blood plasma from patients with cancer. Most techniques employed for ctDNA detection are time consuming and require expensive DNA purification kits. Electrochemiluminescence resonance energy transfer (ECL-RET) biosensors exhibit high sensitivity, a wide response range, and are promising for straightforward sensing applications. Until now, ECL-RET biosensors have been designed for sensing short single-stranded oligonucleotides of less than 45 nucleotides. In this work, an ECL-RET biosensor comprising graphitic carbon nitride quantum dots was assessed for the amplification-free detection in the blood plasma of DNA molecules coding for the EGFR L858R mutation, which is associated with non-small-cell lung cancer. Following a low-cost pre-treatment, the highly specific ECL-RET biosensor quantified double-stranded EGFR L858R DNA of 159 nucleotides diluted into the blood within a linear range of 0.01 fM to 1 pM, demonstrating its potential for noninvasive biopsies.

[Production of lactate from carbon fixation by cyanobacteria: development and prospect].

Lactate is an important industrial chemical and widely used in various industries. In recent years, with the increasing demand for polylactic acid (PLA), the demand for lactate raw materials is also increasing. The contradiction between the high cost and the market demand caused by the heterotrophic production of lactate attracts researchers to seek other favorable solutions. The production of lactate from photosynthetic carbon fixation by cyanobacteria is a potential new raw material supply strategy. Based on the photosynthetic autotrophic cell factory, it can directly produce high optical purity lactate from carbon dioxide on a single platform driven by solar energy. The raw materials are cheap and easy to obtain, the process is simple and controllable, the products are clear and easy to separate, and the double effects of energy saving and emission reduction and production of high value-added products are achieved at the same time, which has important research and application value. This paper reviews the development history of cyanobacteria carbon sequestration to produce lactate, summarizes its research progress and encounters technical difficulties from the aspects of metabolic basis, metabolic engineering strategy, metabolic kinetics analysis and technical application, and prospects the future of this technology.

Optimizing the electrical conductivity of polyacrylonitrile/polyaniline with nickel nanoparticles for the enhanced electrostimulation of Schwann cells proliferation.

Tissue engineering scaffolds made of biocompatible polymers are promising alternatives for nerve reparation. For this application, cell proliferation will be speeded up by electrostimulation, which required electrically-conductive materials. Here, a biomimicking scaffold with optimized conductivity was developed from electrospun polyacrylonitrile/electrically-conductive polyaniline (PAN/PANI) nanofibers doped with Ni nanoparticles. PAN/PANI/Ni was biocompatible for Schwann cells and exhibited a suitable tensile strength and wettability for cell proliferation. When compared with unmodified PAN/PANI, the electrical conductivity of PAN/PANI/Ni was 6.4 fold higher. Without electrostimulation, PAN/PANI and PAN/PANI/Ni exhibited similar Schwann cells' proliferation rates. Upon electrostimulation at 100 mV cm-1 for one hour per day over five days, PAN/PANI/Ni accelerated Schwann cells' proliferation 2.1 times compared to PAN/PANI. These results demonstrate the importance of expanding the electrical conductivity of the tissue engineering scaffold to ensure optimal electrostimulation of nerve cell growth. Additionally, this study describes a straightforward approach to modulate the electrical conductivity of polymeric materials via the addition of Ni nanoparticles that can be applied to different biomimicking scaffolds for nerve healing.

Photo-augmented PHB production from CO2 or fructose by Cupriavidus necator and shape-optimized CdS nanorods.

Particulate photocatalysts developed for the solar energy-driven reduction of the greenhouse gas CO2 have a small product range and low specificity. Hybrid photosynthesis expands the number of products with photocatalysts harvesting sunlight and transferring charges to microbes harboring versatile metabolisms for bioproduction. Besides CO2, abiotic photocatalysts have been employed to increase microbial production yields of reduced compounds from organic carbon substrates. Most single-reactor hybrid photosynthesis systems comprise CdS assembled in situ by microbial activity. This approach limits optimization of the morphology, crystal structure, and crystallinity of CdS for higher performance, which is usually done via synthesis methods incompatible with life. Here, shape and activity optimized CdS nanorods were hydrothermally produced and subsequently applied to Cupriavidus necator for the heterotrophic and autotrophic production of the bioplastic polyhydroxybutyrate (PHB). C. necator with CdS NR under light produced 1.5 times more PHB when compared to the same bacterium with suboptimal commercially-available CdS. Illuminated C. necator with CdS NR synthesized 1.41 g PHB from fructose over 120 h and 28 mg PHB from CO2 over 48 h. Interestingly, the beneficial effect of CdS NR was specific to C. necator as the metabolism of other microbes often employed for bioproduction including yeast and bacteria was negatively impacted. These results demonstrate that hybrid photosynthesis is more productive when the photocatalyst characteristics are optimized via a separated synthesis process prior to being coupled with microbes. Furthermore, bioproduction improvement by CdS-based photocatalyst requires specific microbial species highlighting the importance of screening efforts for the development of performant hybrid photosynthesis.

Improved robustness of microbial electrosynthesis by adaptation of a strict anaerobic microbial catalyst to molecular oxygen.

Microbial electrosynthesis (MES) and other bioprocesses such as syngas fermentation developed for energy storage and the conversion of carbon dioxide into valuable chemicals often employs acetogens as microbial catalysts. Acetogens are sensitive to molecular oxygen, which means that bioproduction reactors must be maintained under strict anaerobic conditions. This requirement increases cost and does not eliminate the possibility of O2 leakage. For MES, the risk is even greater since the system generates O2 when water splitting is the anodic reaction. Here, we show that O2 from the anode of a MES reactor diffuses into the cathode chamber where strict anaerobes reduce CO2. To overcome this drawback, a stepwise adaptive laboratory evolution (ALE) strategy is used to develop the O2 tolerance of the acetogen Sporomusa ovata. Two heavily-mutated S. ovata strains growing well autotrophically in the presence of 0.5 to 5% O2 were obtained. The adapted strains were more performant in the MES system than the wild type converting electrical energy and CO2 into acetate 1.5 fold faster. This study shows that the O2 tolerance of acetogens can be increased, which leads to improvement of the performance and robustness of energy-storage bioprocesses such as MES where O2 is an inhibitor.

Fast removal of toxic hexavalent chromium from an aqueous solution by high-density Geobacter sulfurreducens.

Hexavalent chromium (Cr(VI)) is a carcinogenic compound that can be removed from contaminated sites by the activity of metal-reducing bacteria. The model bacterium Geobacter sulfurreducens reduces Cr(VI) to less toxic Cr(III) and accumulates Cr ions intracellularly. However, this process is usually slow with small concentrations of Cr(VI) removed in a matter of days. Here, high-density G. sulfurreducens cultures were tested for the capacity to remove Cr(VI) readily. With an initial G. sulfurreducens density of 5.8 × 108 cells ml-1, 99.0 ± 0.8% of 100 mg l-1 Cr(VI) was removed after 20 min. With a higher starting Cr(VI) concentration of 200 mg l-1, G. sulfurreducens with a density of 11.4 × 108 cells ml-1 removed 99.0 ± 0.4% Cr(VI) after 2 h. Experiments performed with cell-free spent medium indicate that extracellular proteins are major contributors for the reduction of Cr(VI) to Cr(III). Furthermore, results show that most Cr(III) ions ultimately end up inside the bacterial cells where they are less susceptible to re-oxidation. The fast Cr(VI) removal rates observed with high-density G. sulfurreducens demonstrate the potential of this bacterium for bioremediation applications such as the cleaning of industrial wastewaters.

The facile and controllable synthesis of a bacterial cellulose/polyhydroxybutyrate composite by co-culturing Gluconacetobacter xylinus and Ralstonia eutropha.

Bacterial cellulose (BC) and polyhydroxybutyrate (PHB) are microbial polymers considered to be promising biodegradable alternatives to fossil fuel derivatives. BC and PHB can be combined into a composite with enhanced mechanical properties. The synthesis processes of BC/PHB composites described until now are complicated with multiple steps. Here, BC/PHB composites were synthesized by a facile Gluconacetobacter xylinus and Ralstonia eutropha co-culture method generating BC and PHB simultaneously in situ. This co-culture approach ensured a certain level of control over the synthesis process. By simply varying the R. eutropha inoculum, the weight ratio of PHB into BC/PHB was adjusted from 15.62 to 42.88 %. The fabricated composites were networks of BC fibers connecting PHB particles. BC/PHBs were characterized by thermal and mechanical analyses and exhibited a 2.6 times higher capacity for toxic copper adsorption than pure BC. The co-culture technique described here is a simple synthesis method to obtain BC/PHB with adjustable characteristics.

Graphene: An Antibacterial Agent or a Promoter of Bacterial Proliferation?

Graphene materials (GMs) are being investigated for multiple microbiological applications because of their unique physicochemical characteristics including high electrical conductivity, large specific surface area, and robust mechanical strength. In the last decade, studies on the interaction of GMs with bacterial cells appear conflicting. On one side, GMs have been developed to promote the proliferation of electroactive bacteria on the surface of electrodes in bioelectrochemical systems or to accelerate interspecies electron transfer during anaerobic digestion. On the other side, GMs with antibacterial properties have been synthesized to prevent biofilm formation on membranes for water treatment, on medical equipment, and on tissue engineering scaffolds. In this review, we discuss the mechanisms and factors determining the positive or negative impact of GMs on bacteria. Furthermore, we examine the bacterial growth-promoting and antibacterial applications of GMs and debate their practicability.