Microbial Attachment Research Articles

Enhancement of bioelectricity generation by a microbial fuel cell using Ti nanoparticle‐modified carbon electrode

AbstractBACKGROUNDMicrobial fuel cells (MFCs) are promising devices that can be used to generate electricity from organic wastewater through microbial redox reactions. Various strategies have been attempted to improve the power generation of MFCs, including electrode modification. Titanium (Ti) is a biocompatible metal which is commonly used in various applications. This study examined the improvement of voltage generation by Ti nanoparticle attachment to the carbon electrode surface of an MFC by simple dipping and e‐beam evaporation. Two microbes, namely Shewanella oneidensis MR‐1 and Klebsiella pneumoniae L17, having different electron transfer mechanisms were used to identify the effects of Ti nanoparticles on bioelectricity generation.RESULTSVoltage generation was significantly increased for the MFCs containing Ti nanoparticles, both using S. oneidensis MR‐1 and K. pneumoniae L17. Higher concentrations of DNA extracted from the electrode surface indicated that the Ti nanoparticles did not only assist the electron transfer process from the bacteria to the electrode but also microbial attachment on the carbon electrode. Energy‐dispersive X‐ray spectroscopy (EDS) experiments demonstrated the sustainability of the Ti nanoparticles, showing no significant changes in the attached Ti nanoparticles during an operation period of 3 weeks.CONCLUSIONIt was demonstrated that the Ti‐dipping method is applicable to MFCs as an electrode modification strategy by Ti nanoparticle formation, leading to a similar level of voltage generation (but through a much simpler process) as compared with conventional evaporation methods. © 2019 Society of Chemical Industry

Adaptation to Host-Specific Bacterial Pathogens Drives Rapid Evolution of a Human Innate Immune Receptor

The selective pressure by infectious agents is a major driving force in the evolution of humans and other mammals. Members of the carcinoembryonic antigen-related cell adhesion molecule (CEACAM) familyserve as receptors for bacterial pathogens of the genera Haemophilus, Helicobacter, Neisseria, and Moraxella, which engage CEACAMs via distinct surface adhesins. While microbial attachment to epithelial CEACAMs facilitates host colonization, recognition by CEACAM3, a phagocytic receptor expressed by granulocytes, eliminates CEACAM-binding bacteria. Sequence analysis of primate CEACAM3 orthologs reveals that this innate immune receptor is one of the most rapidly evolving human proteins. In particular, the pathogen-binding extracellular domain of CEACAM3 shows a high degree of non-synonymous versus synonymous nucleotide exchanges, indicating an exceptionally strong positive selection. Using CEACAM3 domains derived from different primates, we find that the amino acid alterations found in CEACAM3 translate into characteristic binding patterns for bacterial adhesins. One such amino acid residue is F62 in human and chimp CEACAM3, which is not present in other primates and which is critical for binding the OMP P1 adhesin of Haemophilus aegyptius. Incorporation of the F62-containing motif into gorilla CEACAM3 results in a gain-of-function phenotype with regard to phagocytosis of H.aegyptius. Moreover, CEACAM3 polymorphisms found in human subpopulations widen the spectrum of recognized bacterial adhesins, suggesting an ongoing multivariate selection acting on this innate immune receptor. The species-specific detection of diverse bacterial adhesins helps to explain theexceptionally fast evolution of CEACAM3 within the primate lineage and provides an example of Red Queen dynamics in the human genome.

Anaerobic Bioreduction of Jarosites and Biofilm Formation by a Natural Microbial Consortium

Jarosite occurs naturally in acid sulphate soils and is a common feature of streams impacted by acid mine drainage (AMD). Biological reduction of iron-sulphate minerals, such as jarosite, has the potential to contribute to the natural attenuation of acid mine drainage sites. The reduction of different jarosites (including minerals containing precious and toxic metals) by a natural bacterial/microbial consortium was examined in this study. Jarosites was used as a sole terminal electron acceptor via the reductive dissolution of Fe(III) minerals. The production of Fe(II) and the presence of sulphate-reducing bacteria in the consortium lead to the precipitation of metal sulphides immobilizing toxic heavy metals. Microbial attachment and biofilm formation of minerals have a great impact on the production and transformation of minerals and can influence the mobility of metals. After the adaptation to different jarosites, a unique specie was found: Desulfosporosinus orientis. Desulfosporosinus species are sulphate-reducing bacteria and can be found in sulphate-rich heavy metal-polluted environments, such as acid mine/rock drainage sites, being responsible for the sulphides formation. D. orientis is an obligate anaerobic microorganism and is able to reduce Fe(III) D. orientis is an obligate anaerobic microorganism and is able to reduce Fe(III). Confocal laser scanning microscopy and fluorescent lectin-binding analyses (FLBA) were used to study the arrangement and composition of the exopolysaccharides/glycoconjugates in biofilms indicating the presence of mannose, glucose, and N-acetylglucosamine residues. This study provides insights to understand the processes leading to the mobility or retention of metals in mine waste and industrial landfill environments.

Isolation of wheat bran-colonizing and metabolizing species from the human fecal microbiota.

Undigestible, insoluble food particles, such as wheat bran, are important dietary constituents that serve as a fermentation substrate for the human gut microbiota. The first step in wheat bran fermentation involves the poorly studied solubilization of fibers from the complex insoluble wheat bran structure. Attachment of bacteria has been suggested to promote the efficient hydrolysis of insoluble substrates, but the mechanisms and drivers of this microbial attachment and colonization, as well as subsequent fermentation remain to be elucidated. We have previously shown that an individually dependent subset of gut bacteria is able to colonize the wheat bran residue. Here, we isolated these bran-attached microorganisms, which can then be used to gain mechanistic insights in future pure culture experiments. Four healthy fecal donors were screened to account for inter-individual differences in gut microbiota composition. A combination of a direct plating and enrichment method resulted in the isolation of a phylogenetically diverse set of species, belonging to the Bacteroidetes, Firmicutes, Proteobacteria and Actinobacteria phyla. A comparison with 16S rRNA gene sequences that were found enriched on wheat bran particles in previous studies, however, showed that the isolates do not yet cover the entire diversity of wheat-bran colonizing species, comprising among others a broad range of Prevotella, Bacteroides and Clostridium cluster XIVa species. We, therefore, suggest several modifications to the experiment set-up to further expand the array of isolated species.

Intestinal microbes direct CX3CR1+ cells to balance intestinal immunity

ABSTRACT Intestinal damage driven by unrestricted immune responses against the intestinal microbiota can lead to the development of inflammatory diseases including inflammatory bowel disease. How such breakdown in tolerance occurs alongside the mechanisms to reinforce homeostasis with the microbiota are a focus of many studies. Our recent work demonstrates coordinated interactions between intact microbiota and CX3CR1 expressing intestinal antigen presenting cells (APCs) that limits T helper 1 cell responses and promotes differentiation of regulatory T cells (Treg) against intestinal antigens including pathogens, soluble proteins and the microbiota itself. We find a microbial attachment to intestinal epithelial cells is necessary to support these anti-inflammatory immune functions. In this addendum, we discuss how our findings enhance understanding of microbiota-directed homeostatic functions of the intestinal immune system and implications of modulating this interaction in ameliorating inflammatory disease.

Effective anti-biofouling enabled by surface electric disturbance from water wave-driven nanogenerator

Biofouling has been a long-last problem in a variety of marine systems which causes energy waste and device damage. In this study, we present a self-activated anti-biofouling system enabled by electrical double layer disturbance, which could effectively suppress the initial formation of conditioning layers and subsequent microbe attachment. The small and low-frequency alternating electrical fields were produced by a triboelectric nanogenerator under water wave impacts. Systematic analyses confirmed that the anti-biofouling efficacy was directly related to the strength of the electric field and was effective in both fresh lake and sea water environments. An on-site demonstration was implemented at a calm lake shore for three weeks. The water wave-driven anti-biofouling exhibited excellent surface protection, which was significantly superior to several commercial anti-biofouling coatings. This development brings an effective and eco-friendly solution for protecting a broad range of surfaces against biofouling.

Fucosyltransferase Gene Polymorphisms and Lewisb-Negative Status Are Frequent in Swedish Newborns, With Implications for Infectious Disease Susceptibility and Personalized Medicine.

Single-nucleotide polymorphisms (SNPs) in the fucosyltransferase genes FUT2 and FUT3 have been associated with susceptibility to various infectious and inflammatory disorders. FUT variations influence the expression of human histo-blood group antigens (HBGAs) (H-type 1 and Lewis), which are highly expressed in the gut and play an important role in microbial attachment, metabolism, colonization, and shaping of the microbiome. In particular, FUT polymorphisms confer susceptibility to specific rotavirus and norovirus genotypes, which has important global health implications. We designed a genotyping method using a nested polymerase chain reaction approach to determine the frequency of SNPs in FUT2 and FUT3, thereby inferring the prevalence of Lewisb-positive, Lewisb-negative, secretor, and nonsecretor phenotypes in 520 Swedish newborns. There was an increased frequency of homozygotes for the minor allele for 1 SNP in FUT2 and 4 SNPs in FUT3. Overall, 37.3% of newborns were found to have Lewis b negative phenotypes (Le (a+b-) or Le (a-b-). Using our new, sensitive genotyping method, we were able to genetically define the Le (a-b-) individuals based on their secretor status and found that the frequency of Lewis b negative newborns in our cohort was 28%. Given the high frequency of fucosyltransferase polymorphisms observed in our newborn cohort and the implications for disease susceptibility, FUT genotyping might play a future role in personalized health care, including recommendations for disease screening, therapy, and vaccination.

PVA/CS and PVA/CS/Fe gel beads' synthesis mechanism and their performance in cultivating anaerobic granular sludge

Biomass washout from high-speed anaerobic suspended bed bio-reactors is still a challenge to their stable operation. Preserving active biomass to efficiently retain biomass in the reactor is one of the solutions to this problem. Herein, two carriers (polyvinyl alcohol/chitosan (PVA/CS) and PVA/CS/Fe gel beads) were prepared using the cross-linking method. The fourier transform infrared (FTIR) and 13C nuclear magnetic resonance (13C NMR) analyses showed that PVA/CS gel beads formed mainly through hydrogen-bonds (NH2OH-). Furthermore, FTIR, 13C NMR, energy dispersive spectrum (EDS), X-ray diffractometer (XRD) and X-ray photoelectron spectroscopy (XPS) analyses showed that PVA/CS/Fe gel beads formed mainly through chelate bond (NH2-FeM+OH-). The scanning electron microscope (SEM) results affirmed that the gel beads had rough and well-developed porous structure for the attachment of microbes. Furthermore, the abilities of gel beads on the cultivation of granular sludge in an up-flow anaerobic sludge bed (UASB) reactor were effectively demonstrated while treating wastewater polluted with glucose and alkali lignin. The results showed that the gel beads-assisted reactors had a higher performance than those without the gel beads. The cultivation of granules in these reactors was accelerated, while the granules became bigger and exhibited better settling velocities. The reactor with gel beads was easier to withstand a higher organic loading rate due to dense microbial aggregates, which were caused by more humic-like substance. Particularly, the reactor with PVA/CS/Fe gel beads was able to improve the overall robustness of the system due to stronger mechanical properties of gel beads, and also prevented cells detachment.

Effect of Zeolite-Fe on graphite anode in electroactive biofilm development for application in microbial fuel cells

The performance of microbial fuel cells (MFCs) is highly dependent on the electrode materials. The electrode surface can be modified to provide a favorable environment for biofilms to enhance electron transfer from the bacteria to the anode. In this work, Faujasite zeolite-Y (ZY) was exchanged with iron (Fe) and was used to modify glassy carbon/graphite electrodes (GC/gr-ZYFe) evaluating its effect in electroactive biofilm development for application in microbial fuel cells. The novel material was evaluated as an anode in MFCs by comparing its performance with GC/gr and GC/gr-ZY electrodes. The results show that when using a GC/gr-ZYFe electrode, an electroactive biofilm with good electrochemical activity for acetate degradation can be generated on the electrode surface. The maximum current density obtained with a GC/gr-ZYFe-BF electrode (where BF is biofilm) was 7.7 times higher than that of a GC/gr anode. The modification generates a less hydrophobic electrode surface that facilitates microbial cell attachment, thereby improving bioelectricity production. By using scanning electron microscopy, a homogeneous microbial community with bacteria that had a similar short rod-shaped morphology was observed. Furthermore, electrochemical impedance spectroscopy demonstrated that the charge transfer resistance (Rct) decreased as the biofilm grew, revealing that the presence of the biofilm facilitated the electrochemical reaction. After 7 days of MFC operation, the GC/gr-ZYFe bioanode showed a reduction in Rct from 212.9 ± 1.81 Ω to 151.5 ± 1.46 Ω, which was 2.4 times lower than that achieved with GC/gr. The biofilm on GC/gr-ZYFe was characterized using cyclic voltammetry, and the results showed a larger oxidation peak (169.8 μA cm−2) than that of the GC/gr electrode (36.5μA cm−2), further supporting the better electron-transfer properties of the modified electrode. Additionally, this result confirms the capability of biofilms to act as bioelectrocatalysts under acetate-oxidizing conditions.

Hydrocarbon contaminated water remediation using a locally constructed multi-stage bioreactor incorporated with media filtration

The present study investigated the coupling effect of biodegradation and media filtration in treating hydrocarbon contaminated water. The study recorded reductions in total petroleum hydrocarbon, total dissolved solids, turbidity and microbial load. The study was essentially a simulated pump and treat process that involved the pumping of hydrocarbon contaminated water for treatment in a locally designed multi-stage bioreactor incorporated with media filtration. A mixed consortium of hydrocarbon-eating microbes was applied in the study. Hydrocarbon-eating microbes were isolated from hydrocarbon contaminated soils obtained from selected mechanic workshops. Bamboo chips and coconut husk chips were applied as support media for microbial attachment within the bioreactor compartment of the treatment setup. Applied support media were approximately 2-4 cm in size. Media filters applied comprised three locally manufactured candle filters two of which were respectively impregnated with granular activated charcoal and sand. The coupling effect of biodegradation and media filtration recorded over 99 % (> 8.7 mg/L) total petroleum hydrocarbon removal. Microbial load reduction ranged from 3.57±0.11E+20 to 7.45±0.26E+20 Colony forming unit/mL, total dissolved solids reduction from 30.00±5.66 to 131.00±0.00 mg/L and turbidity reduction from 39.00±1.41 to 123.50±0.71 nephelometric turbidity units. Biodegradation accounted for 69.70±0.63 and 90.72±2.36 % total petroleum hydrocarbon removal respectively for bamboo chips and coconut husk chips.

Development of thin-film composite membranes via radical grafting with methacrylic acid/ ZnO doped TiO2 nanocomposites

The surface nanostructure of polyamide thin film composite membrane PA(TFC) has been improved for reverse osmosis water desalination using synthesized (ZnO/TiO2) nanocomposites (NCs) incorporated into the hydrophilic methacrylic acid (MAA) grafting solution. The membrane modification has been achieved using PA(TFC) functionalized with (ZnO/TiO2) NCs. The synthesized (ZnO/TiO2) NCs and membrane surface properties were characterized using the Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), Scanning electron microscope (SEM) and Contact angle (CA). Additionally, membrane performances have been evaluated. The preliminary results indicate that the (ZnO/TiO2) NCs are considerably developing the membrane performances in terms of water flux, salt rejection, mechanical properties, fouling resistances, stability in acidic-alkaline solutions and bio-antifouling properties of the PA(TFC) membranes. The (ZnO/TiO2/PMAA)-g-PA(TFC) NCs membrane showed salt rejection of 96.8% and water flux of 33.3 L/m2·h using15 bar applied pressure and a saline NaCl solution of 2000 mg/L. Furthermore, the modified membrane has greatly enhanced the fouling resistance of the Bovine Serum Albumin (BSA) as a potential fouling and inhibits microbial attachment and biofilm growing onto the membrane surfaces using E. coli as a foulant model.

A Fully-Papertronic Biosensing Array for High-Throughput Characterization of Microbial Electrogenicity.

For the first time, we report a low-cost, disposable fully-papertronic screening platform for rapid screening and identification of electroactive microorganisms. This novel papertronic device is capable of simultaneous characterizing the electrogenicity of 10' s of the newly discovered, genetically engineered, bacteria. This work explored an exciting range of possibilities with the goal of fusing microbial fuel cell technology with 'papertronics,' the emerging field of paper-based electronics. Spatially distinct 64 sensing units of the array were constructed by patterning hydrophilic anodic reservoirs in paper with hydrophobic wax boundaries and utilizing 3-D multi-laminate paper structures. Full integration of a high-performance microbial sensor on paper can be achieved by improving the microbial electron exchange with the electrodes in an engineered conductive paper reservoir and reducing cathodic overpotential by using a solid electron acceptor on paper. Furthermore, the intrinsic capillary force of the paper and the increased capacity from the engineered reservoir allowed for rapid adsorption of the bacterial sample and promote immediate microbial cell attachment to the electrode, leading to instant power generation with even a small amount of the liquid.

Wastewater Treatment and Biogas Recovery Using Anaerobic Membrane Bioreactors (AnMBRs): Strategies and Achievements

Anaerobic digestion is one of the most essential treatment technologies applied to industrial and municipal wastewater treatment. Membrane-coupled anaerobic bioreactors have been used as one alternative to the conventional anaerobic digestion process. They are presumed to offer the advantage of completely reducing or minimizing the volume of sludge and increasing biogas production. However, researchers have consistently reported different kinds of fouling that resulted in the reduction of membrane life span. Depending on the strength of the effluent, factors such as high suspended and dissolved solids, fats, oil and grease, transmembrane pressure (TMP) and flux were reported as major contributors to the membrane fouling. Moreover, extracellular polymeric substances (EPSs) are an important biological substance that defines the properties of sludge flocs, including adhesion, hydrophobicity and settling and have been found to accelerate membrane fouling as well. Extensive studies of AnMBR have been done at laboratory while little is reported at the pilot scale. The significance of factors such as organic loading rates (OLRs), hydraulic retention time (HRT), pH and temperature on the operations of AnMBRs have been discussed. Microbial environmental conditions also played the most important role in the production of biogas and the chemical oxygen demand (COD) removal, but adverse effects of volatile fatty acids formation were reported as the main inhibitory effect. Generally, evaluating the potential parameters and most cost effective technology involved in the production of biogas and its inhibitory effects as well as the effluent quality after treatment is technically challenging, thus future research perspectives relating to food to microorganism F/M ratio interaction, sufficient biofilm within the reactor for microbial attachment was recommended. For the purpose of energy savings and meeting water quality discharge limit, the use of micro filtration was also proposed.

Experimental Microbial Alteration and Fe Mobilization From Basaltic Rocks of the ICDP HSDP2 Drill Core, Hilo, Hawaii

The interaction of a single bacterial species (Burkholderia fungorum) with basaltic rocks from the ICDP HSDP2 drill core and synthetic basaltic glasses was investigated in batch laboratory experiments to better understand the role of microbial activity on rock alteration and Fe mobilization. Incubation experiments were performed with drill core basaltic rock samples to investigate differences in the solution chemistry during biotic and abiotic alteration. Additionally, colonization experiments with synthetic basaltic glasses of different Fe redox states and residual stresses were performed to evaluate their influence on microbial activity and surface attachment of cells. In biotic incubation experiments bacterial growth was observed and the release of Fe and other major elements from drill core basaltic rocks to solution exceeded that of abiotic controls only when the rock sample assay was nutrient depleted. The concentration of dissolved major elements in solution in biotic colonization experiments with synthetic basaltic glasses increased with increasing residual stress and Fe(II) content. Furthermore, the concentration of dissolved Fe and Al increased similarly in biotic colonization experiments indicating that their dissolution might be triggered by microbial activity. Surface morphology imaging by SEM revealed that cells on basaltic rocks in incubation experiments were most abundant on the glass and surfaces with high roughness and almost absent on minerals. In colonization experiments, basaltic glasses with residual stress and high Fe(II) content were intensely covered with a cellular biofilm. In contrast, glasses with high Fe(III) content and no residual stress were sparsely colonized. We therefore conclude that structurally bound Fe is most probably used by B. fungorum as a nutrient. Furthermore, we assume that microbial activity overall increased rock dissolution as soon as the environment becomes nutrient depleted. Our results show that besides compositional effects, other factors such as redox state and residual stress can control microbial alteration of basaltic glasses.

Bioinspired Photocatalytic Shark-Skin Surfaces with Antibacterial and Antifouling Activity via Nanoimprint Lithography.

By combining antifouling shark-skin patterns with antibacterial titanium dioxide (TiO2) nanoparticles (NPs), we present a simple route toward producing durable multifunctional surfaces that decrease microbial attachment and inactivate attached microorganisms. Norland Optical Adhesive, a UV-crosslinkable adhesive material, was loaded with 0, 10, or 50 wt % TiO2 NPs from which shark-skin microstructures were imprinted using solvent-assisted soft nanoimprint lithography on a poly(ethylene terephthalate) (PET) substrate. To obtain coatings with an exceptional durability and an even higher concentration of TiO2 NPs, a solution containing 90 wt % TiO2 NPs and 10 wt % tetraethyl orthosilicate was prepared. These ceramic shark-skin-patterned surfaces were fabricated on a PET substrate and were quickly cured, requiring only 10 s of near infrared (NIR) irradiation. The water contact angle and the mechanical, antibacterial, and antifouling characteristics of the shark-skin-patterned surfaces were investigated as a function of TiO2 composition. Introducing TiO2 NPs increased the contact angle hysteresis from 30 to 100° on shark-skin surfaces. The hardness and modulus of the films were dramatically increased from 0.28 and 4.8 to 0.49 and 16 GPa, respectively, by creating ceramic shark-skin surfaces with 90 wt % TiO2 NPs. The photocatalytic shark-skin-patterned surfaces reduced the attachment of Escherichia coli by ∼70% compared with smooth films with the same chemical composition. By incorporating as low as 10 wt % TiO2 NPs into the chemical matrix, over 95% E. coli and up to 80% Staphylococcus aureus were inactivated within 1 h UV light exposure because of the photocatalytic properties of TiO2. The photocatalytic shark-skin-patterned surfaces presented here were fabricated using a solution-processable and roll-to-roll compatible technique, enabling the production of large-area high-performance coatings that repel and inactivate bacteria.

Enhancing the biodegradation rate of poly(lactic acid) films and PLA bio-nanocomposites in simulated composting through bioaugmentation

Biodegradable polymers provide an opportunity to divert plastic waste from landfills, with composting as an alternative disposal route. However, some biodegradable polymers, such as poly (lactic acid) (PLA), do not biodegrade as fast as other organic wastes during composting, affecting their general acceptance in industrial composting facilities. Bioaugmentation, the addition of specific microbial strains, is a promising technique to accelerate the biodegradation of compostable plastics, so that they biodegrade in comparable time frames with other organic materials. In this study, we evaluated the effect of bioaugmentation on the biodegradation of PLA and PLA bio-nanocomposites (BNCs) in simulated composting conditions. PLA, PLA with 5% organo-modified montmorillonite (PLA-OMMT5), and PLA with 0.4% surfactant (PLA-QAC0.4) films were produced and fully characterized. PLA-degrading bacteria were isolated through an enrichment technique with PLA as the sole carbon source at 58 °C. Isolates were identified as Geobacillus using 16 S rRNA gene sequencing and the NCBI database, and further used to study the effect of bioaugmentation on the biodegradation rate of PLA and BNCs in solid environments. The biotic and abiotic degradation was assessed in compost, inoculated vermiculite, and uninoculated vermiculite at 58 °C by analysis of evolved CO2 using an in-house built direct measurement respirometer. Size exclusion chromatography was also used to measure and to monitor the change in molecular weight of the film samples retrieved every week during the biodegradation test. The microbial attachment on the surface of PLA of the isolated microbial strain and other microorganisms present in the compost was evaluated by a biofilm forming assay in wells incubated at 58 °C. Bioaugmentation with Geobacillus increased the evolution of CO2 and accelerated the biodegradation phase of PLA and BNCs when tested in compost and inoculated vermiculite with compost mixed culture. Bioaugmentation could commercially be used to accelerate the biodegradation of PLA in compost environments.

The attachment potential and N-acyl-homoserine lactone-based quorum sensing in aerobic granular sludge and algal-bacterial granular sludge.

Bacteria and algae often coexist in the aerobic granular sludge (AGS) system in a photo-bioreactor, forming algal-bacterial granular sludge. In this study, the physicochemical characteristics and microbial attachment potential of the AGS and algal-bacterial granular sludge were comparatively analyzed. Results clearly showed that the larger and denser algal-bacterial granular sludge had stronger attachment potential compared to the AGS (as the control). A bioassay with Agrobacterium tumefaciens KYC55 indicated that N-acyl-homoserine lactones (AHLs) existed in both sludge types, but further investigations revealed that the relative AHL content of the algal-bacterial granular sludge obviously increased and slightly decreased during phases II and III, respectively, but was consistently higher than the AGS. Based on the EPS measurements and 3D-excitation-emission matrix (3D-EEM) fluorescence spectra analysis, the enhancement of AHL-based QS favored the hydrophobic protein production of algal-bacterial granular sludge, contributing to a good development of the granular sludge. In addition, it was also found that inhibition of AHLs resulted in the reduction of the protein content and attachment potential in algal-bacterial granular sludge, which was unfavorable to the structural stability of the granules. High-throughput sequencing analysis showed that the microbial community of AGS was different from the algal-bacterial granular sludge; specifically, algal-bacterial granulation facilitated the abundance of AHLs and EPS producers, such as the genera Acinetobacter, Chryseobacterium, and Flavobacterium.

Optimization of dilute acetic acid pretreatment of mixed fruit waste for increased methane production

Abstract A proper waste management practice such as anaerobic digestion for the waste generated by the agro-food industries could minimize the amount of material disposal to landfill. In our study, the improvement of methane production was elucidated through the pretreatment optimization of the mixed fruit wastes (FW). Dilute acetic acid pretreatment of FW was optimized in order to increase the bioavailability and microbial accessibility. A maximum sugar recovery of 95% was achieved from the pretreated FW under the optimized conditions (0.2 M acetic acid, 62.5 °C, and 30 min). Fourier transform infrared spectroscopy (FTIR) and Thermogravimetric (TG) analyses verified the presence of cellulosic material in the pretreated FW. X-ray diffraction (XRD) analysis indicated that the crystallinity index was increased to 56% after the disruption of complex hemicellulosic structures during pretreatment. Increased porosity and surface roughness of pretreated FW for better microbial attachment were confirmed in scanning electron microscopy (SEM). Anaerobic digestion showed increased methanogenic activity (10.17 mL g−1 VSinitial d−1) in pretreated FW, during 86-day experimental period due to better microbial attachment and accessibility during the digestion process. Higher methane yield of 53.58 mL g−1 VSinitial was observed in pretreated FW. Thus, acetic acid pretreatment is an effective method to improve the utilization and conversion of FW to methane.

Dynamic Dispersal of Surface Layer Biofilm Induced by Nanosized TiO2 Based on Surface Plasmon Resonance and Waveguide.

Pollutant degradation is present mainly in the surface layer of biofilms, and the surface layer is the most vulnerable to impairment by toxic pollutants. In this work, the effects of nanosized TiO2 (n-TiO2) on the average thicknesses of Bacillus subtilis biofilm and on bacterial attachment on different surfaces were investigated. The binding mechanism of n-TiO2 to the cell surface was also probed. The results revealed that n-TiO2 caused biofilm dispersal and the thicknesses decreased by 2.0 to 2.6 μm after several hours of exposure. The attachment abilities of bacteria with extracellular polymeric substances (EPS) on hydrophilic surfaces were significantly reduced by 31% and 81% under 10 and 100 mg/liter of n-TiO2, respectively, whereas those of bacteria without EPS were significantly reduced by 43% and 87%, respectively. The attachment abilities of bacteria with and without EPS on hydrophobic surfaces were significantly reduced by 50% and 56%, respectively, under 100 mg/liter of n-TiO2 The results demonstrated that biofilm dispersal can be attributed to the changes in the cell surface structure and the reduction of microbial attachment ability.IMPORTANCE Nanoparticles can penetrate into the outer layer of biofilm in a relatively short period and can bind onto EPS and bacterial surfaces. The current work probed the effects of nanosized TiO2 (n-TiO2) on biofilm thickness, bacterial migration, and surface properties of the cell in the early stage using the surface plasmon resonance waveguide mode. The results demonstrated that n-TiO2 decreased the adhesive ability of both cell and EPS and induced bacterial migration and biofilm detachment in several hours. The decreased adhesive ability of microbes and EPS worked against microbial aggregation, reducing the effluent quality in the biological wastewater treatment process.

Preparation of ordered mesoporous and macroporous thermoplastic polyurethane surfaces for potential medical applications.

Thermoplastic polyurethanes are widely used in medical devices. In order to limit some of their shortfalls, like microbial attachment, surfaces modifications can be required. In this work, a two-step replication method was used to create ordered macroporous and mesoporous thermoplastic polyurethane surfaces using anodic aluminum oxide as master template. The intermediate mould materials that were tested were polystyrene and a polyacrylate resin with inorganic filler. All obtained surfaces were characterized by scanning electron microscopy. The initial anodic aluminum oxide surfaces possessed macro or mesopores, function of anodization conditions. The intermediate mould structure correctly replicated the pattern, but the polystyrene surface structures (pillars) were less resistant than the polyacrylate resin ones. The thermoplastic polyurethane pattern possessed macropores or mesopores of about 130 nm or 46 nm diameter and of about 300 nm or 99 nm interpore distances, respectively, in accordance with the initial pattern. Thermoplastic polyurethanes pore depth was however less than initial anodic aluminum oxide pore depth, linked to an incomplete replication during intermediate mould preparation (60 to 90% depth replication). The correct replication of the original pattern confirms that this novel fabrication method is a promising route for surface patterning of thermoplastic polyurethanes that could be used for medical applications.