Comparison of contact angle measurement and microbial adhesion to solvents for assaying electron donor-electron acceptor (acid-base) properties of bacterial surface

Chlorination of Pseudomonas aeruginosa in potable water

The present study examined the effects of chlorine (NaOCl) disinfection on Pseudomonas aeruginosa in potable water. The adhesion of the bacteria on glass surfaces and the growth of the adherent cells were measured after treatment with chlorine (0, 0.25, 0.5, 0.75, and 1 mg/L). Adhesion was assessed by optical microscopy, and cultivability of the adherent cells was estimated by counting the bacteria on solid medium after being recovered from the support surface. Regardless of the concentration applied, P. aeruginosa did not lose the ability to adhere or grow after adhesion. However, the two factors were influenced by the chlorine treatments. The results showed that the adhesive capacity and cultivability of adherent cells were linked. The maximum inhibition of adherence and cultivability was observed in the 0.25 and 0.5 mg/L treatments. At 0.75 and 1 mg/L, the adhesive capability and post-adhesive cultivability were slightly increased. The results suggest that residual concentrations of sodium hypochlorite fixed by standards (less than 1 mg/L) may be ineffective against P. aeruginosa, and thus could have an impact on consumers.

Flexible nanohybrid substrates utilizing gold nanocubes/nano mica platelets with 3D lightning-rod effect for highly efficient bacterial biosensors based on surface-enhanced Raman scattering

In this study, gold nanocubes (AuNCs) were quickly synthesized using the seed-mediated growth method and reduced onto the surface of two-dimensional (2D) delaminated nano mica platelets (NMPs), enabling the development of AuNCs/NMPs nanohybrids with a 3D lightning-rod effect. First, the growth-solution amount can be changed to easily adjust the AuNCs average-particle size within a range of 30-70 nm. The use of the cationic surfactant cetyltrimethylammonium chloride as a protective agent allowed the surface of AuNCs and nanohybrids to be positively charged. Positively charged nanohybrid surfaces presented a good adsorption effect for detecting molecules with negative charges on the surface. Additionally, the NMP surfaces were rich in ionic charges and provided a large specific surface area for stabilizing the growth of AuNCs. Delaminated AuNCs/NMPs nanohybrids can generate a 3D hotspot effect through self-assembly to enhance the Raman signal. Surface-enhanced Raman scattering (SERS) is highly sensitive in detecting adenine biomolecules. Its limit of detection (LOD) and Raman enhancement factor reached 10-9 M and 3.6 × 108, respectively. Excellent reproducibility was obtained owing to the relatively regular arrangement of AuNC particles, and the relative standard deviation (RSD) was 10.7%. Finally, the surface of NMPs was modified by adding the hydrophilic poly(oxyethylene)-diamine (POE2000) and amphiphilic PIB-POE-PIB copolymer at different weight ratios. The adjustment of the surface hydrophilicity and hydrophobicity of AuNCs/NMPs nanohybrids led to better adsorption and selectivity for bacteria. AuNCs/POE/NMPs and AuNCs/PIB-POE-PIB/NMPs were further applied to the SERS detection of hydrophilic Staphylococcus aureus and hydrophobic Escherichia coli, respectively. The SERS-detection results suggest that the LOD of hydrophilic Staphylococcus aureus and hydrophobic Escherichia coli reached 92 CFU mL-1 and 1.6 × 102 CFU mL-1, respectively. The AuNCs/POE/NMPs and AuNCs/PIB-POE-PIB/NMPs nanohybrids had different hydrophilic-hydrophobic affinities, which greatly improved the selectivity and sensitivity for detecting bacteria with different hydrophilicity and hydrophobicity. Therefore, fast, highly selective, and highly sensitive SERS biological-detection results were obtained.

Characterization of Streptomyces Cell Surface by the Microbial Adhesion to Solvents Method

The cell surface physicochemical properties of Streptomyces should influencing the dispersal and adsorption of spores and hyphae in soil and should conditioning there interactions with organic or metal substances in the bioremediation of contaminated environment. These properties are concerning surface hydrophobicity, electron donor/acceptor, and charge surface. To date, only hydrophobicity of Streptomyces was studied by contact angle measurements and microbial adhesion to hydrocarbons (MATH). In this work, we studied the electron donor/acceptor character of the Streptomyces cell surface in two ionic strength 10^-3 M and 10^-1 M of KNO₃. Thus, to facilitate the characterisation of the surfaces of microbial cells, we used a simple, rapid, and quantitative technique, the microbial adhesion method to solvents (MATS), which is based on the comparison of the affinity of microbial cells for a monopolar solvent with a polar solvent. The monopolar solvent can be acid (electron acceptor) or basic (electron donor), but both solvents should have a surface tension similar to that of the Kifshitz van der Waals components. At the significant ionic strength of the biological medium, the electron donor character is well expressed for all 14 Streptomyces strains with very significant differences among them ranging from 0% to 72.92%. When the cells were placed in a solution with a higher ionic strength, we were able to classify the donor character results into three categories. The first category is that the weak donor character of strains A53 and A58 became more expressed at 10^-1 M KNO₃ concentration. The second category is that three strains A30, A60, and A63 expressed a weaker character in a higher ionic strength. For the other strains, no expression of the donor trait was obtained at higher ionic strength. In a suspension with a concentration of 10^-3 KNO₃, only two strains expressed an electron acceptor character. This character is very important for strains A49, A57, A58, A60, A63, and A65 at 10^-1M KNO₃. This work has shown that these properties vary greatly depending on the Streptomyces strain. It is important to consider the change in physicochemical properties of surface cells with ionic strength when using Streptomyces in different bioprocesses.

Efficient biosynthesis of (R)-mandelic acid from styrene oxide by an adaptive evolutionary Gluconobacter oxydans STA

BACKGROUND

(R)-mandelic acid (R-MA) is a highly valuable hydroxyl acid in the pharmaceutical industry. However, biosynthesis of optically pure R-MA remains significant challenges, including the lack of suitable catalysts and high toxicity to host strains. Adaptive laboratory evolution (ALE) was a promising and powerful strategy to obtain specially evolved strains.

RESULTS

Herein, we report a new cell factory of the Gluconobacter oxydans to biocatalytic styrene oxide into R-MA by utilizing the G. oxydans endogenous efficiently incomplete oxidization and the epoxide hydrolase (SpEH) heterologous expressed in G. oxydans. With a new screened strong endogenous promoter P₁₂₇₈₀, the production of R-MA was improved to 10.26 g/L compared to 7.36 g/L of using P_lac. As R-MA showed great inhibition for the reaction and toxicity to cell growth, adaptive laboratory evolution (ALE) strategy was introduced to improve the cellular R-MA tolerance. The adapted strain that can tolerate 6 g/L R-MA was isolated (named G. oxydans STA), while the wild-type strain cannot grow under this stress. The conversion rate was increased from 0.366 g/L/h of wild type to 0.703 g/L/h by the recombinant STA, and the final R-MA titer reached 14.06 g/L. Whole-genome sequencing revealed multiple gene-mutations in STA, in combination with transcriptome analysis under R-MA stress condition, we identified five critical genes that were associated with R-MA tolerance, among which AcrA overexpression could further improve R-MA titer to 15.70 g/L, the highest titer reported from bulk styrene oxide substrate.

CONCLUSIONS

The microbial engineering with systematic combination of static regulation, ALE, and transcriptome analysis strategy provides valuable solutions for high-efficient chemical biosynthesis, and our evolved G. oxydans would be better to serve as a chassis cell for hydroxyl acid production.

Microbial Responses to Various Types of Chemical Regents during On-Line Cleaning of UF Membranes

Ultrafiltration is widely used to treat various environmental waters, and on-line membrane cleaning with various chemical reagents is frequently employed to sustain the filtration flux. However, the residue of cleaning agents in the ultrafiltration system is unavoidable, which may affect microbiological properties and biofilm formation during the next-round filtration. By investigating the changes in microbial characteristics, and their biofouling behaviors after exposure to HCl, NaOH, NaClO, citric acid (CA), and sodium dodecyl sulfonate (SDS), this study fills a knowledge gap in microbial responses to various types of chemical cleaning agents in an ultrafiltration system. The result shows that HCl, NaOH, and NaClO affect the bacterial properties and subsequent attachment on the membrane surface, while CA and SDS have no obvious influence on microorganisms. Specifically, HCl, NaOH, and NaClO reduce the hydrophobicity and mean size of suspended microorganisms, increase the extracellular polymeric substances (EPS) release, and trigger intracellular reactive oxygen species (ROS) generation, resulting in the death of a large quantity of microorganisms. Due to the self-protecting strategy, plenty of living cells aggregate on the membrane surface and form a cake layer with a stratified structure, causing more severe membrane biofouling.

Adhesion Behavior of Escherichia coli Strains on Glass: Role of Cell Surface Qualitative and Quantitative Hydrophobicity in Their Attachment Ability

Microbial adhesion to surfaces is thought to involve physicochemical interactions between the substrate and microbial cells. Understanding the physicochemical aspects involved in the adhesion phenomenon, as a critical step in biofilm formation, is essential to finding ways to prevent their formation and control biocontamination risks. The aim of this study was to investigate the relation between the adhesion behavior of 12 Escherichia coli strains isolated from food and their surface hydrophobicities using qualitative (θ _w ) and quantitative (ΔG _iwi ) approaches. The surface physicochemical properties of both bacterial cells and glass material were estimated through contact angle measurements. The adhesive behavior of E. coli strains on a glass surface was assessed. The results showed a good logarithmic relation between the percentage of the adhered cells and their surface hydrophobicity with the quantitative approach ΔG _iwi ; however, qualitative hydrophobicity (θ _w ) appeared to demonstrate no effect regarding adhesion behavior. This work lays the foundation for future studies and opens an important debate on the mechanisms underlying the adhesion behavior of E. coli strains by using the thermodynamic approach (ΔG _iwi ) as an important model of hydrophobicity that could explain and predict better bacterial adhesion ability.

Identification of CO2 induces oxidative stress to change bacterial surface properties

The surface properties of bacteria play an essential role in their abilities to perform transmembrane communication, adherence, immobilization, flocculation, etc. However, the responsiveness of bacterial surfaces to elevated atmospheric CO₂ remains unknown. In this study, using the model bacteria, Paracoccus denitrificans, the effect of CO₂ on the primary bacterial surface properties, specifically hydrophobicity and surface charge, has been explored. We found that hydrophilicity and negative surface charge both rose in conjunction with increased atmospheric CO₂ concentrations. Studies of the potential mechanisms involved have illustrated that elevated CO₂ significantly increases the production of polysaccharides in extracellular polymeric substances (EPS). Various hydrophilic groups and negative charges in these polysaccharides prompt hydrophilicity and surface charge variations in bacteria. Further research has identified that elevations in CO₂ result in the accumulation of reactive species, specifically reactive nitrogen species (RNS). In this study, it was found that RNS damaged the permeability of bacterial membranes by inducing lipid peroxidation and then caused the leakage of intracellular substrate, which ultimately led to an increase in EPS polysaccharides. Our findings suggest that changes in bacterial surface properties due to atmospheric CO₂ elevation, as well as the reactions these trigger, merit widespread attention.

Efficient chemical hydrophobization of lactic acid bacteria - One-step formation of double emulsion

A novel concept of stabilizing multiple-phase food structure such as emulsion using solely the constitutional bacteria enables an all-natural food grade formulation and thus a clean label declaration. In this paper, we propose an efficient approach to hydrophobically modifying the surface of lactic acid bacteria Lactobacillus rhamnosus (LGG) using lauroyl ahloride (LC) in non-aqueous media. Compared to the unmodified bacteria, cell hydrophobicity was dramatically altered upon modification, according to the higher percentages of microbial adhesion to hexadecane (MATH) and water contact angles (WCA) of LC-modified bacteria. No evident changes were found in bacterial surface charge before and after LC modification. By using one-step homogenization, all the modified bacteria were able to generate stabile water-in-oil-in-water (W/O/W) double emulsions where bacteria were observed on oil-water interfaces of the primary and secondary droplets. Modification using high LC concentrations (10 and 20 w/w%) led to rapid autoaggregation of bacteria in aqueous solution. A long-term lethal effect of modification primarily came from lyophilization and no apparent impact was detected on the instantaneous culturability of modified bacteria.

The theoretical adhesion of Pseudomonas aeruginosa and Escherichia coli on some plumbing materials in presence of distilled water or tap water

The main aim of this work was to determine the most appropriate materials for the installation of a water system according to the characteristics of the water that passes through it. To this end, we conducted an investigation of the effect of two types of water (SDW: sterile distilled water and STW: sterile tap water) on the properties of bacterial surfaces and the theoretical adhesion of two bacteria (Pseudomonas aeruginosa and Escherichia coli) on six plumbing materials. Contact angle measurements were used to determine the surface energies of bacteria and materials. XDLVO theory was used to estimate the interactions between bacteria and plumbing materials. The results showed that water had a clear impact on the electron donor character and the hydrophobicity of the bacterial surfaces. Also, the predictive adhesion showed that all tested materials could be colonized by P. aeruginosa and E. coli ([Formula: see text]<0). However, colonization became thermodynamically less favorable or unfavorable (increase in [Formula: see text] values) with SDW and STW, respectively. Finally, the results suggest that the choice of the most suitable material for a drinking water installation is related to the quality of the water itself.

Impacts of carrier properties, environmental conditions and extracellular polymeric substances on biofilm formation of sieved fine particles from activated sludge

To investigate the effect of properties of carriers, environmental conditions and extracellular polymeric substances (EPS) on the initial adhesion of biofilm formation in biofilm-based reactors, a quartz crystal microbalance with dissipation (QCM-D) was applied to monitor the deposition rates and viscoelastic properties of sieved sludge particles on model biocarriers. The results suggested that surface charge, hydrophobicity and surface coating of five representative carriers influenced deposition rates and viscoelastic properties of biofilm, whose variation with NaCl concentrations was controlled by not only the Derjaguin-Landau-Verwey-Overbeek (DLVO) interaction but also non-DLVO forces. On hydrophobic surface, the addition of cationic substances enhanced the deposition rates and the compaction of deposited layer due to strong "hydrophobizing effect". For examples, 10 mM Ca²⁺, 10 mM Mg²⁺ and 10 mg/L poly-l-lysine enhanced the deposition rates to nearly 3, 2 and 4 times, as well as reduced the softness of deposited layer to almost 35%, 60% and 35%. Conversely, 10 mg/L negatively charged alginate might cause water retainment and steric shielding, thereby reducing the deposition rates to 40% and increasing the softness of deposited film to 120%. The presence of EPS sub-fractions can modify surface properties of sludge particles, to distinct degrees, contributing to biofilm formation. Notably, compared to tightly bound EPS (TB-EPS), loosely bound EPS (LB-EPS) was more conducive to microbial attachment, but the presence of LB-EPS promoted the formation of a soft layer on a hydrophobic surface. Overall, these results provide insights into intrinsic mechanisms of the variation of deposition rates and viscoelastic properties responding to critical factors, which are meaningful to predict and regulate the initial adhesion process in biofilm-based reactors.

Analyzing the effect of pH on microalgae adhesion by identifying the dominant interaction between cell and surface

Microalgae adhesion plays a critical role in developing effective photobioreactors for large-scale production of microalgae biofuel. This study focused on elucidating the influencing mechanism of liquid medium pH on microalgae adhesion by identifying the dominant interactions between cell and substratum using a criterion. Herein, the adhesion of three microalgae onto two substrata at a series of pH was observed using a flow chamber. The results indicated that the adhesion of freshwater Chlorella sp. onto PVC and glass and marine Chlorella sp. and N. oculata onto glass decreased with increasing pH, because these adhesions were dominated by the EL interaction, and the pH would influence the adhesion primarily by affecting the ζ potential of the cell and substratum. Whereas, the adhesion of marine Chlorella sp. and N. oculata onto PVC increased with increasing pH, because these adhesions were dominated by Lewis acid-base (AB) interaction, and the pH would influence the adhesion primarily by affecting the components of surface free energy of cell. The study demonstrated that the influencing mechanism of pH on adhesion can be conclusively elucidated by identifying the dominant interaction between the cell and the surface, and may have significant implications for predicting cell adhesion in various applications.

Particle assisted removal of microbes from surfaces

Increased reliance on kill based approaches for disinfection raises concerns of antimicrobial resistance development and has significantly elevated the need for alternate approaches for skin and substrate disinfection. This study focuses on reducing harmful microbes from substrates primarily via removal and to a lesser extent by kill.

HYPOTHESIS

Functional micro-particles designed to adhere to microbes, with a force greater than the force of microbial adhesion to the substrate, would result in enhanced removal-based disinfection of substrates when subject to an external force.

EXPERIMENTS

Silica particles were functionalized with a cationic polymer to bind strongly with bacteria via Coulombic interactions. Disinfection efficacies of substrates with functional particles and control groups were evaluated under conditions relevant for handwashing.

FINDINGS

Functionalized silica micro-particles result in ∼4 log reduction of E. coli from an artificial skin substrate in 30 s as compared to a maximum of 1.5 log reduction with control particles. Bacterial viability assays indicate a mechanism of action driven by enhanced removal of bacteria with minimal kill. Particle number density, size and suspension velocity along with strong particle - bacteria interactions have been found to be the primary factors responsible for the enhanced bacterial removal from surfaces.

Aciduric Strains of Lactobacillus reuteri and Lactobacillus rhamnosus, Isolated from Human Feces, Have Strong Adhesion and Aggregation Properties

Human feces were streaked onto MRS Agar adjusted to pH 2.5, 3.0, and 6.4, respectively, and medium supplemented with 1.0% (w/v) bile salts. Two aciduric strains, identified as Lactobacillus reuteri HFI-LD5 and Lactobacillus rhamnosus HFI-K2 (based on 16S rDNA and recA sequences), were non-hemolytic and did not hydrolyze mucin. The surface of Lactobacillus reuteri HFI-LD5 cells has a weak negative charge, whereas Lactobacillus rhamnosus HFI-K2 has acidic and basic properties, and produces exopolysaccharides (EPS). None of the strains produce bacteriocins. Both strains are resistant to several antibiotics, including sulfamethoxazole-trimethoprim and sulphonamides. The ability of Lactobacillus reuteri HFI-LD5 and Lactobacillus rhamnosus HFI-K2 to grow at pH 2.5 suggests that they will survive passage through the stomach. EPS production may assist in binding to intestinal mucus, especially in the small intestinal tract, protect epithelial cells, and stimulate the immune system. Lactobacillus reuteri HFI-LD5 and Lactobacillus rhamnosus HFI-K2 may be used as probiotics, especially in the treatment of small intestinal bacterial overgrowth (SIBO).

Modeling Escherichia coli and Rhodococcus erythropolis transport through wettable and water repellent porous media

Water protection and bioremediation strategies in the vadose zone require understanding the factors controlling bacterial transport for different hydraulic conditions. Breakthrough experiments were made in two different flow conditions: i) an initial bacteria pulse under ponded infiltration into dry sand (-15,000 cm); ii) a second bacteria pulse into the same columns during subsequent infiltration in constant water content and steady-state flow. Escherichia coli (E. coli) and Rhodococcus erythropolis (R. erythropolis) were used to represent hydrophilic and hydrophobic bacteria, respectively. Equilibrium and attachment/detachment models were tested to fit bromide (Br^-) and bacteria transport data using HYDRUS-1D. Derjaguin-Landau-Verwey-Overbeek (DLVO) and extended DVLO (XDLVO) interaction energy profiles were calculated to predict bacteria sorption at particles. Adsorption of bacteria at air-water interfaces was estimated by a hydrophobic force approach. Results suggested greater retention of bacteria in water repellent sand compared with wettable sand. Inverse parameter optimization suggested that physico-chemical attachment of both E. coli and R. erythropolis was thousands of times lower in wettable than repellant sand and straining was 10-fold lower in E. coli for wettable vs repellant sand compared to the exact opposite by orders of magnitude with R. erythropolis. HYDRUS did not provide a clear priority of importance of solid-water or air-water interfaces in bacteria retention. Optimized model parameters did not show a clear relation to the (X)DLVO adsorption energies. This illustrated the ambivalence of (X)DLVO to predict bacterial attachment at solid soil particles of different wetting properties. Simultaneous analysis of mass recovery, numerical modeling, and interaction energy profiles thus suggested irreversible straining due to bacteria sizing as dominant compared to attachment to liquid-solid or liquid-air interfaces. Further studies are needed to distinguish straining mechanisms (i.e. pore structure or film straining) in different hydraulic conditions.

Application of Bdellovibrio bacteriovorus for reducing fouling of membranes used for wastewater treatment

Background:

Membrane bioreactor (MBR) systems used for wastewater treatment (WWT) processes are regarded as clean technologies. Degradation capacity of the predator bacterium, Bdellovibrio bacteriovorus, was used as a cleaning strategy for reducing membrane fouling.

Method:

Wastewater with different sludge age and hydraulic retention time were filtered through Poly(ether)sulphone (PES) membranes using dead end reactor. Change in filtration performance after cleaning of membrane surface by B. bacteriovorus was measured by comparison of flux values. Bacterial community of the sludge was determined by 16SrRNA sequence analysis. Community profile of membrane surface was analyzed by fluorescent in situ hybridization technique.

Results:

After cleaning of MP005 and UP150 membranes with predator bacteria, 4.8 L/m2·h and 2.04 L/m2·h increase in stable flux at steady state condition was obtained as compared to the control, respectively. Aeromonas, Proteus, and Alcaligenes species were found to be dominant members of the sludge. Bdellovibrio bacteriovorus lysed pure cultures of the isolated sludge bacteria successfully. FISH analysis of the membrane surface showed that Alfa-proteobacteria are the most numerous bacteria among the biofilm community on the membrane surface.

Conclusion:

Results suggested that cleaning of MBR membranes with B. bacteriovorus has a potential to be used as a biological cleaning method.

Effect of a novel potential probiotic Lactobacillus paracasei Jlus66 isolated from fermented milk on nonalcoholic fatty liver in rats

Nonalcoholic fatty liver disease (NAFLD) is the main cause of chronic liver disease worldwide. Previous evidence indicates that probiotics can be applied as a therapeutic agent for NAFLD. In this study, the potential probiotic strain Lactobacillus paracasei Jlus66 was isolated from natural fermented milk by a culture-dependent method, and its probiotic potentials were tested by established in vitro tests. In addition, the protective effect of Lactobacillus paracasei Jlus66 against NAFLD was evaluated in rat models. Compared with the high-fat-diet (HFD) group, the rats administered with 4 × 10¹⁰ cfu Jlus66 had significantly lower body weight gain, serum triglyceride (TG), low-density lipoprotein (LDL) as well as aminotransferase (ALT). Histopathological analysis showed Jlus66 also reduced the level of hepatic triglycerides and steatosis. From the above we conclude that L. paracasei Jlus66 has great potential as a probiotic in protecting from NAFLD.

The effective migration of Massilia sp. WF1 by Phanerochaete chrysosporium and its phenanthrene biodegradation in soil

Pollutant-degrading bacteria migrated by fungi may enhance the contacts between microorganisms and pollutants and improve the bioremediation efficiency of persistent organic pollutants in soil. Here, the migration of phenanthrene (PHE)-degrading bacteria Massilia sp. WF1 and Mycobacterium sp. WY10 by the hydrophobic fungi Phanerochaete chrysosporium (P. chrysosporium) and its effects on the PHE biodegradation in soil were investigated. Migration of the hydrophilic bacterium WF1 was better than that of the hydrophobic bacterium WY10 by P. chrysosporium mycelia since strain WF1 possesses flagellum and the type III secretion system. The interaction energy change of P. chrysosporium-WF1 was lower, but the interaction forces (van der Waals attractions, capillary forces, and cross-linking effects) were stronger than those of P. chrysosporium-WY10. Thus, the adhesive attraction between strain WF1 and P. chrysosporium was stronger, and consequently, strain WF1 was migrated by P. chrysosporium to a greater extent than WY10. The corresponding migration mechanism was inferred to be a bacterial 'passive' method: bacteria adhered to mycelia before they migrated with the growing mycelia. Moreover, migrated strain WF1 via P. chrysosporium showed effective PHE biodegradation in soil. Fungus-mediated migration of pollutant-degrading bacteria may play an important role in the bioremediation of pollutants in soil.

Production, optimization and probiotic characterization of potential lactic acid bacteria producing siderophores

The aim of the study was to characterize the probiotic qualities and siderophore production of Enterococcus and Bacillus isolates for possible application for iron nutrition in human and animals strains were selectively isolated from different dairy sources and infant faecal matter. Isolates SB10, JC13 and IFM22 were found to produce maximum siderophore ranging from 65–90% at an optimum pH 7, incubation period of 96 h, agitation speed of 150 rpm and inoculum volume of 15%. SB10 and JC13 were found to show high homology with Enterococcus spp. and IFM22 with Bacillus spp., using partial 16S rRNA sequencing and biochemical characterization. All the three isolates produced hydroxymate type of siderophores under iron stressed conditions and screened for probiotic characters as per WHO guidelines. Strains have shown excellent tolerance to acid, bile salt, sodium chloride and phenol. They were non-haemolytic in nature and exhibited high hydrophobicity and autoaggregation. Our isolates proved to be potent probiotic strains due to their survival under highly acidic conditions and higher tolerance to bile salt. In addition, its colonization efficiency was proved by exhibiting high autoaggregation and hydrophobicity.

Effect of preconditioning cobalt and nickel based dental alloys with Bacillus sp. extract on their surface physicochemical properties and theoretical prediction of Candida albicans adhesion

Biofilm formation on dental biomaterials is implicated in various oral health problems. Thus the challenge is to prevent the formation of this consortium of microorganisms using a safe approach such as antimicrobial and anti-adhesive natural products. Indeed, in the present study, the effects of an antifungal extract of Bacillus sp., isolated from plant rhizosphere, on the surface physicochemical properties of cobalt and nickel based dental alloys were studied using the contact angle measurements. Furthermore, in order to predict the adhesion of Candida albicans to the treated and untreated dental alloys, the total free energy of adhesion was calculated based on the extended Derjaguin-Landau-Verwey-Overbeek approach. Results showed hydrophobic and weak electron-donor and electron-acceptor characteristics of both untreated dental alloys. After treatment with the antifungal extract, the surface free energy of both dental alloys was influenced significantly, mostly for cobalt based alloy. In fact, treated cobalt based alloy became hydrophilic and predominantly electron donating. Those effects were time-dependent. Consequently, the total free energy of adhesion of C. albicans to this alloy became unfavorable after treatment with the investigated microbial extract. A linear relationship between the electron-donor property and the total free energy of adhesion has been found for both dental alloys. Also, a linear relationship has been found between this latter and the hydrophobicity for the cobalt based alloy. However, the exposure of nickel based alloy to the antifungal extract failed to produce the same effect.

Bacterial physiology is a key modulator of the antibacterial activity of graphene oxide

Carbon-based nanomaterials have a great potential as novel antibacterial agents; however, their interactions with bacteria are not fully understood. This study demonstrates that the antibacterial activity of graphene oxide (GO) depends on the physiological state of cells for both Gram-negative and -positive bacteria. GO susceptibility of bacteria is the highest in the exponential growth phase, which are in growing physiology, and stationary-phase (non-growing) cells are quite resistant against GO. Importantly, the order of GO susceptibility of E. coli with respect to the growth phases (exponential ≫ decline > stationary) correlates well with the changes in the envelope ultrastructures of the cells. Our findings are not only fundamentally important but also particularly critical for practical antimicrobial applications of carbon-based nanomaterials.

Mechanobiology of Antimicrobial Resistant Escherichia coli and Listeria innocua

A majority of antibiotic-resistant bacterial infections in the United States are associated with biofilms. Nanoscale biophysical measures are increasingly revealing that adhesive and viscoelastic properties of bacteria play essential roles across multiple stages of biofilm development. Atomic Force Microscopy (AFM) applied to strains with variation in antimicrobial resistance enables new opportunities for investigating the function of adhesive forces (stickiness) in biofilm formation. AFM force spectroscopy analysis of a field strain of Listeria innocua and the strain Escherichia coli K-12 MG1655 revealed differing adhesive forces between antimicrobial resistant and nonresistant strains. Significant increases in stickiness were found at the nanonewton level for strains of Listeria innocua and Escherichia coli in association with benzalkonium chloride and silver nanoparticle resistance respectively. This advancement in the usage of AFM provides for a fast and reliable avenue for analyzing antimicrobial resistant cells and the molecular dynamics of biofilm formation as a protective mechanism.

DNA microarray of global transcription factor mutant reveals membrane-related proteins involved in n-butanol tolerance in Escherichia coli

BACKGROUND

Escherichia coli has been explored as a platform host strain for biofuels production such as butanol. However, the severe toxicity of butanol is considered to be one major limitation for butanol production from E. coli. The goal of this study is therefore to construct butanol-tolerant E. coli strains and clarify the tolerance mechanisms.

RESULTS

A recombinant E. coli strain harboring σ(70) mutation capable of tolerating 2 % (v/v) butanol was isolated by the global transcription machinery engineering (gTME) approach. DNA microarrays were employed to assess the transcriptome profile of butanol-tolerant strain B8. Compared with the wild-type strain, 329 differentially expressed genes (197 up-regulated and 132 down-regulated) (p < 0.05; FC ≥ 2) were identified. These genes are involved in carbohydrate metabolism, energy metabolism, two-component signal transduction system, oxidative stress response, lipid and cell envelope biogenesis and efflux pump.

CONCLUSIONS

Several membrane-related proteins were proved to be involved in butanol tolerance of E. coli. Two down-regulated genes, yibT and yghW, were identified to be capable of affecting butanol tolerance by regulating membrane fatty acid composition. Another down-regulated gene ybjC encodes a predicted inner membrane protein. In addition, a number of up-regulated genes, such as gcl and glcF, contribute to supplement metabolic intermediates for glyoxylate and TCA cycles to enhance energy supply. Our results could serve as a practical strategy for the construction of platform E. coli strains as biofuel producer.

Control of bacterial adhesion and growth on honeycomb-like patterned surfaces

It is a great challenge to construct a persistent bacteria-resistant surface even though it has been demonstrated that several surface features might be used to control bacterial behavior, including surface topography. In this study, we develop micro-scale honeycomb-like patterns of different sizes (0.5-10 μm) as well as a flat area as the control on a single platform to evaluate the bacterial adhesion and growth. Bacteria strains, Escherichia coli and Staphylococcus aureus with two distinct shapes (rod and sphere) are cultured on the platforms, with the patterned surface-up and surface-down in the culture medium. The results demonstrate that the 1 μm patterns remarkably reduce bacterial adhesion and growth while suppressing bacterial colonization when compared to the flat surface. The selective adhesion of the bacterial cells on the patterns reveals that the bacterial adhesion is cooperatively mediated by maximizing the cell-substrate contact area and minimizing the cell deformation, from a thermodynamic point of view. Moreover, study of bacterial behaviors on the surface-up vs. surface-down samples shows that gravity does not apparently affect the spatial distribution of the adherent cells although it indeed facilitates bacterial adhesion. Furthermore, the experimental results suggest that two major factors, i.e. the availability of energetically favorable adhesion sites and the physical confinements, contribute to the anti-bacterial nature of the honeycomb-like patterns.

Reducing Staphylococcus aureus growth on Ti alloy nanostructured surfaces through the addition of Sn

β-type Ti alloys containing Nb are exciting materials for numerous orthopedic and dental applications due to their exceptional mechanical properties. To improve their cytocompatibility properties (such as increasing bone growth and decreasing infection), the surfaces of such materials can be optimized by adding elements and/or nanotexturing through anodization. Because of the increasing prevalence of orthopedic implant infections, the objective of this in vitro study was to add Sn and create unique nanoscale surface features on β-type Ti alloys. Nanotubes and nanofeatures on Ti-35Nb and Ti-35Nb-4Sn alloys were created by anodization in a HF-based electrolyte and then heat treated in a furnace to promote amorphous structures and phases such as anatase, a mixture of anatase-rutile, and rutile. Samples were characterized by SEM, which indicated different morphologies dependent on the oxide content and method of modification. XPS experiments identified the oxide content which resulted in a phase transformation in the oxide layer formed onto Ti-35Nb and Ti-35Nb-4Sn alloys. Most importantly, regardless of the resulting nanostructures (nanotubes or nanofeatures) and crystalline phase, this study showed for the first time that adding Sn to β-type Ti alloys strongly decreased the adhesion of Staphylococcus aureus (S. aureus; a bacteria which commonly infects orthopedic implants leading to their failure). Thus, this study demonstrated that β-type Ti alloys with Nb and Sn have great promise to improve numerous orthopedic applications where infection may be a concern.

Structural, Surface, in vitro Bacterial Adhesion and Biofilm Formation Analysis of Three Dental Restorative Composites

This study was conducted to investigate the relationship between dental materials and bacterial adhesion on the grounds of their chemical composition and physical properties. Three commercially available dental restorative materials (Filtek™Z350, Filtek™P90 and Spectrum^®TPH^®) were structurally analyzed and their wettability and surface roughness were evaluated by using Fourier Transform Infrared Spectroscopy, Contact Angle Measurement and Atomic Force Microscopy, respectively. These materials were molded into discs and tested with three bacterial strains (Staphylococcus aureus, Pseudomonas aeruginosa and Escherichia) for microbial attachment. The bacterial adhesion was observed at different time intervals, i.e., 0 h, 8 h, 24 h, 48 h and 72 h, along with Colony Forming Unit Count and Optical Density measurement of the media. It was found that all materials showed a degree of conversion with time intervals, i.e., 0 h, 8 h, 24 h, 48 h and 72 h, which led to the availability of functional groups (N–H and C–H) that might promote adhesion. The trend in difference in the extent of bacterial adhesion can be related to particle size, chemical composition and surface wettability of the dental materials.

Thermodynamic prediction of growth temperature dependence in the adhesion of Pseudomonas aeruginosa and Staphylococcus aureus to stainless steel and polycarbonate

This study investigated the effect of growth temperature changes (20, 30, and 37°C) on the adhesion behavior of Pseudomonas aeruginosa and Staphylococcus aureus to stainless steel and polycarbonate. Adhesion assays were performed under static conditions at 20°C. In addition, the validity of the thermodynamic and extended Derjaguin, Landau, Verwey, and Overbeek theories as predictive tools of bacterial adhesion were studied. The surface properties of the bacterial cells and the substrates of attachment were characterized, and atomic force microscopy was used to analyze the surface topography. The results indicated that the highest adhesion rate of P. aeruginosa and S. aureus on both surfaces was observed when the cells were grown at 37°C. The bacterial adhesion to stainless steel was found to be two times higher than to polycarbonate for both bacteria, whatever the condition used. The present study underlined that the thermodynamic and the extended Derjaguin, Landau, Verwey, and Overbeek theories were able to partially predict the empirical results of P. aeruginosa adhesion. However, these theories failed to predict the adhesion behavior of S. aureus to both surfaces when the growth temperature was changed. The results of the microbial adhesion to solvent indicated that the adhesion rate to abiotic surfaces may correlate with the hydrophobicity of bacterial surfaces. The effect of surface topography on bacterial adhesion showed that surface roughness, even on the very low nanometer scale, has a significant effect on bacterial adhesion behavior.

Success and failure of colloidal approaches in adhesion of microorganisms to surfaces

Biofilms are communities of cells attached to surfaces, their contributions to biological process may be either a benefit or a threat depending on the microorganism involved and on the type of substrate and environment. Biofilm formation is a complex series of steps; due to the size of microorganisms, the initial phase of biofilm formation, the bacterial adhesion to the surface, has been studied and modeled using theories developed in colloidal science. In this review the application of approaches such as Derjaguin, Landau, Verwey, Overbeek (DLVO) theory and its extended version (xDLVO), to bacterial adhesion is described along with the suitability and applicability of such approaches to the investigation of the interface phenomena regulating cells adhesion. A further refinement of the xDLVO theory encompassing the brush model is also discussed. Finally, the evidences of phenomena neglected in colloidal approaches, such as surface heterogeneity and fluid flow, likely to be the source of failure are defined.

Impact of the exopolysaccharides Pel and Psl on the initial adhesion of Pseudomonas aeruginosa to sand

In this study, the impact of the exopolysaccharides Pel and Psl on the cell surface electron donor-electron acceptor (acid-base) properties and adhesion to quartz sand was investigated by using Pseudomonas aeruginosa PAO1 and its isogenic EPS-mutant strains Δpel, Δpsl and Δpel/Δpsl. The microbial adhesion to hydrocarbon (MATH) test and titration results showed that both Pel and Psl contribute to the surface hydrophobicity of the cell. The results of contact angle measurement, however, showed no correlation with the cell surface hydrophobicity measured by the MATH test and the titration method. Packed-bed column experiments indicated that the exopolysaccharides Pel and Psl are involved in the initial cell attachment to the sand surface and the extent of their impact is dependent on the ionic strength (IS) of the solution. Overall, the Δpel/Δpsl double mutant had the lowest adhesion coefficient to sand compared with the wild-type PAO1, the Δpel mutant and the Δpsl mutant. It is hypothesized that in addition to bacterial surface hydrophobicity and DLVO forces, other factors, eg steric repulsion caused by extracellular macromolecules, and cell surface appendages (flagella and pili) also contribute significantly to the interaction between the cell surface and a sand grain.

Cell surface hydrophobicity of colistin-susceptible vs resistant Acinetobacter baumannii determined by contact angles: methodological considerations and implications

Contact angle analysis of cell surface hydrophobicity (CSH) describes the tendency of a water droplet to spread across a lawn of filtered bacterial cells. Colistin-induced disruption of the Gram-negative outer membrane necessitates hydrophobic contacts with lipopolysaccharide (LPS). We aimed to characterize the CSH of Acinetobacter baumannii using contact angles, to provide insight into the mechanism of colistin resistance. Contact angles were analysed for five paired colistin-susceptible and resistant Ac. baumannii strains. Drainage of the water droplet through bacterial layers was demonstrated to influence results. Consequently, measurements were performed 0·66s after droplet deposition. Colistin-resistant cells exhibited lower contact angles (38·8±2·8-46·8±1·3°) compared with their paired colistin-susceptible strains (40·7±3·0-48·0±1·4°; anova; P<0·05). Contact angles increased at stationary phase (50·3±2·9-61·5±2·5° and 47·4±2·0-50·8±3·2°, susceptible and resistant, respectively, anova; P<0·05) and in response to colistin 32mgl(-1) exposure (44·5±1·5-50·6±2·8° and 43·5±2·2-48·0±2·2°, susceptible and resistant, respectively; anova; P<0·05). Analysis of complemented strains constructed with an intact lpxA gene, or empty vector, highlighted the contribution of LPS to CSH. Compositional outer-membrane variations likely account for CSH differences between Ac. baumannii phenotypes, which influence the hydrophobic colistin-bacterium interaction. Important insight into the mechanism of colistin resistance has been provided. Greater consideration of contact angle methodology is necessary to ensure accurate analyses are performed.