Adhesion and motility of fouling diatoms on a silicone elastomer

Recent demands for non-toxic antifouling technologies have led to increased interest in coatings based on silicone elastomers that ‘release’ macrofouling organisms when hydrodynamic conditions are sufficiently robust. However, these types of coatings accumulate diatom slimes, which are not released even from vessels operating at high speeds ( > 30 knots). In this study, adhesion strength and motility of three common fouling diatoms (Amphora coffeaeformis var. perpusilla (Grunow) Cleve, Craspedostauros australis Cox and Navicula perminuta Grunow) were measured on a polydimethylsiloxane elastomer (PDMSE) and acid-washed glass. Adhesion of the three species was stronger to PDMSE than to glass but the adhesion strengths varied. The wall shear stress required to remove 50% of cells from PDMSE was 17 Pa for Craspedostauros, 24 Pa for Amphora and >> 53 Pa for Navicula; the corresponding values for glass were 3, 10 and 25 Pa. In contrast, the motility of the three species showed little or no correlation between the two surfaces. Craspedostauros moved equally well on glass and PDMSE, Amphora moved more on glass initially before movement ceased and Navicula moved more on PDMSE before movement ceased. The results show that fouling diatoms adhere more strongly to a hydrophobic PDMSE surface, and this feature may contribute to their successful colonization of low surface energy, foul-release coatings. The results also indicate that diatom motility is not related to adhesion strength, and motility does not appear to be a useful indicator of surface preference by diatoms.     

Adhesion and motility of fouling diatoms on a silicone elastomer

Recent demands for non-toxic antifouling technologies have led to increased interest in coatings based on silicone elastomers that 'release' macrofouling organisms when hydrodynamic conditions are sufficiently robust. However, these types of coatings accumulate diatom slimes, which are not released even from vessels operating at high speeds (>30 knots). In this study, adhesion strength and motility of three common fouling diatoms (Amphora coffeaeformis var. perpusilla (Grunow) Cleve, Craspedostauros australis Cox and Navicula perminuta Grunow) were measured on a poly-dimethylsiloxane elastomer (PDMSE) and acid-washed glass. Adhesion of the three species was stronger to PDMSE than to glass but the adhesion strengths varied. The wall shear stress required to remove 50% of cells from PDMSE was 17 Pa for Craspedostauros, 24 Pa for Amphora and >53 Pa for Navicula; the corresponding values for glass were 3, 10 and 25 Pa. In contrast, the motility of the three species showed little or no correlation between the two surfaces. Craspedostauros moved equally well on glass and PDMSE, Amphora moved more on glass initially before movement ceased and Navicula moved more on PDMSE before movement ceased. The results show that fouling diatoms adhere more strongly to a hydrophobic PDMSE surface, and this feature may contribute to their successful colonization of low surface energy, foul-release coatings. The results also indicate that diatom motility is not related to adhesion strength, and motility does not appear to be a useful indicator of surface preference by diatoms.     

A live bioprobe for studying diatom-surface interactions

Atomic force microscopy has been employed to compare the adhesion of Navicula species I diatoms to surfaces of a hydrophobic elastomer, Intersleek, and a hydrophilic mineral, mica. This was accomplished using tipless atomic force microscopy cantilevers functionalized with live diatom cells. Both surfaces were tested with the same diatom bioprobe. Force versus distance curves generated during these experiments revealed comparable cell adhesion strengths on Intersleek and mica, indicating that Navicula diatoms secrete extracellular polymeric substances with hydrophobic and hydrophilic properties. A statistical analysis of force curves was carried out and the average values of works of detachment of a diatom from Intersleek and mica surfaces were determined.     

Microfluidic detachment assay to probe the adhesion strength of diatoms

Fouling release (FR) coatings are increasingly applied as an environmentally benign alternative for controlling marine biofouling. As the technology relies on removing fouling by water currents created by the motion of ships, weakening of adhesion of adherent organisms is the key design goal for improved coatings. In this paper, a microfluidic shear force assay is used to quantify how easily diatoms can be removed from surfaces. The experimental setup and the optimization of the experimental parameters to study the adhesion of the diatom Navicula perminuta are described. As examples of how varying the physico-chemical surface properties affects the ability of diatoms to bind to surfaces, a range of hydrophilic and hydrophobic self-assembled monolayers was compared. While the number of cells that attached (adhered) was barely affected by the coatings, the critical shear stress required for their removal from the surface varied significantly.     

Barnacle settlement and the adhesion of protein and diatom microfouling to xerogel films with varying surface energy and water wettability

Previous work has shown that organosilica-based xerogels have the potential to control biofouling. In this study, modifications of chemistry were investigated with respect to their resistance to marine slimes and to settlement of barnacle cyprids. Adhesion force measurements of bovine serum albumin (BSA)-coated atomic force microscopy (AFM) tips to xerogel surfaces prepared from aminopropylsilyl-, fluorocarbonsilyl-, and hydrocarbonsilyl-containing precursors, indicated that adhesion was significantly less on the xerogel surfaces in comparison to a poly(dimethylsiloxane) elastomer (PDMSE) standard. The strength of adhesion of BSA on the xerogels was highest on surfaces with the highest and the lowest critical surface tensions, γ_C and surface energies, γ_S, and duplicated the ‘Baier curve’. The attachment to and removal of cells of the diatom Navicula perminuta from a similar series of xerogel surfaces were examined. Initial attachment of cells was comparable on all of the xerogel surfaces, but the percentage removal of attached cells by hydrodynamic shear stress increased with γ_C and increased wettability as measured by the static water contact angle, θ_Ws, of the xerogel surfaces. The percentage removal of cells of Navicula was linearly correlated with both properties (R ² = 0.74 for percentage removal as a function of θ_Ws and R ² = 0.69 for percentage removal as a function of γ_C). Several of the aminopropylsilyl-containing xerogels showed significantly greater removal of Navicula compared to a PDMSE standard. Cypris larvae of the barnacle B. amphitrite showed preferred settlement on hydrophilic/higher energy surfaces. Settlement was linearly correlated with θ_Ws (R ² = 0.84) and γ_C (R ² = 0.84). Hydrophilic xerogels should prove useful as coatings for boats in regions where fouling is dominated by microfouling (protein and diatom slimes).     

Surface sensing and stress-signalling in Ulva and fouling diatoms – potential targets for antifouling: a review

Understanding the underlying signalling pathways that enable fouling algae to sense and respond to surfaces is essential in the design of environmentally friendly coatings. Both the green alga Ulva and diverse diatoms are important ecologically and economically as they are persistent biofoulers. Ulva spores exhibit rapid secretion, allowing them to adhere quickly and permanently to a ship, whilst diatoms secrete an abundance of extracellular polymeric substances (EPS), which are highly adaptable to different environmental conditions. There is evidence, now supported by molecular data, for complex calcium and nitric oxide (NO) signalling pathways in both Ulva and diatoms being involved in surface sensing and/or adhesion. Moreover, adaptation to stress has profound effects on the biofouling capability of both types of organism. Targets for future antifouling coatings based on surface sensing are discussed, with an emphasis on pursuing NO-releasing coatings as a potentially universal antifouling strategy.     

Fluorine-free mixed amphiphilic polymers based on PDMS and PEG side chains for fouling release applications

Fluorine-free mixed amphiphilic block copolymers with mixtures of short side groups of polydimethyl siloxane (PDMS) and polyethylene glycol (PEG) were synthesized and studied for their ability to influence the surface properties and control the adhesion of marine organisms to coated surfaces. The settlement (attachment) and strength of adhesion of two different marine algae, the green seaweed Ulva and the diatom Navicula, were evaluated against the surfaces. It is known that hydrophobic coatings based on polydimethyl siloxane elastomers (PDMSe) are prone to protein adsorption and accumulation of strongly adherent diatom slimes, in contrast to PEG-based hydrophilic surfaces that inhibit protein adsorption and moderate only weak adhesion of diatoms. By incorporating both PDMS and PEG side chains into the polymers, the effect of incorporating both polar and non-polar groups on fouling-release could be studied. The dry surfaces were characterized by X-ray photoelectron spectroscopy (XPS) and near-edge X-ray absorption fine structure spectroscopy (NEXAFS). The ability of these mixed amphiphilic polymers to reconstruct in water was examined using underwater bubble contact angle and dynamic water contact angle experiments. To understand more about surface reconstruction behavior, protein adsorption experiments were carried out with fluorescein isothiocyanate-labeled bovine serum albumin (BSA-FITC) on both dry and pre-soaked surfaces.     

New insights into developing antibiofouling surfaces for industrial photobioreactors

The biofouling formation of the marine microalga Nannochloropsis gaditana on nontoxic surfaces was quantified on rigid materials, both coated (with fouling release coatings and nanoparticle coatings) and noncoated, to cover a wide range of surface properties from strongly hydrophobic to markedly hydrophilic under conditions similar to those prevailing in outdoor massive cultures of marine microalgae. The effect of seawater on surfaces that presented the best antibiofouling properties was also evaluated. The adhesion intensity on the different surfaces was compared with the predictions of the biocompatibility theories developed by Baier and Vogler using water adhesion tension (τ⁰) as the quantitative parameter of surface wettability. For the most hydrophobic surfaces, τ⁰ ≤ 0, the microalgae adhesion density increased linearly with τ⁰, following the Baier's theory trend. However, for the rest of the surfaces, τ⁰ ≥ 0, a tendency toward minimum adhesion was observed for amphiphilic surfaces with a τ⁰ = 36 mJ/m², a value close to that which minimizes cell adhesion according to Vogler's theory. The understanding and combination of the two biocompatibility theories could help to design universal antibiofouling surfaces that minimize the van der Waals forces and prevent foulant adsorption by using a thin layer of hydration.     

Evaluation of Bacillus anthracis and Yersinia pestis sample collection from nonporous surfaces by quantitative real‐time PCR

Aim: We will validate sample collection methods for recovery of microbial evidence in the event of accidental or intentional release of biological agents into the environment. Methods and Results: We evaluated the sample recovery efficiencies of two collection methods – swabs and wipes – for both nonvirulent and virulent strains of Bacillus anthracis and Yersinia pestis from four types of nonporous surfaces: two hydrophilic surfaces, stainless steel and glass, and two hydrophobic surfaces, vinyl and plastic. Sample recovery was quantified using real‐time qPCR to assay for intact DNA signatures. We found no consistent difference in collection efficiency between swabs or wipes. Furthermore, collection efficiency was more surface‐dependent for virulent strains than nonvirulent strains. For the two nonvirulent strains, collection efficiency was similar between all four surfaces, albeit B. anthracis Sterne exhibited higher levels of recovery compared to Y. pestis A1122. In contrast, recovery of B. anthracis Ames spores and Y. pestis CO92 from the hydrophilic glass or stainless steel surfaces was generally more efficient compared to collection from the hydrophobic vinyl and plastic surfaces. Conclusions: Our results suggest that surface hydrophobicity may play a role in the strength of pathogen adhesion. The surface‐dependent collection efficiencies observed with the virulent strains may arise from strain‐specific expression of capsular material or other cell surface receptors that alter cell adhesion to specific surfaces. Significance and Impact of the Study: These findings contribute to the validation of standard bioforensics procedures and emphasize the importance of specific strain and surface interactions in pathogen detection.     

Adsorption of bacterial capsular exopolymers to hydrophilic and hydrophobic surfaces: A 2D‐FTIR analysis

Analysis of the adsorption of capsular exopolymers (EPS) from Pseudomonas sp. NCIMB 2021 to hydrophilic and hydrophobic gold surfaces was examined, in situ, using Fourier transform infrared spectroscopy. The molecular sequence of events occurring upon EPS adsorption to hydrophilic and hydrophobic surfaces has been elucidated using dynamic 2D‐FTIR correlation spectroscopy. This method of analysis enables the enhancement of the resolution of overlapping spectral features and the elucidation of time‐dependent changes. The data reveal the existence of surface dependent adsorption mechanisms. At both surfaces, the aromatic tyrosyl side chains of the protein moiety displace water. This is followed by an adsorption step dominated by carboxylate groups. However, at the hydrophobic surface, the two steps are interrupted by the ingress of water back to the surface. Furthermore, the amount of neutral exopolymer present was greater at the hydrophilic surface than the hydrophobic surface.     

Atomic force microscopy and hydrodynamic characterization of the adhesion of <Emphasis Type="Italic">staphylococcus aureus</Emphasis> to hydrophilic and hydrophobic substrata at different pH values

Understanding the mechanism of the bacterial cell adhesion to solid surfaces is of great medical and industrial importance. Bacterial adhesion to inert surfaces, such as a catheter, and other indwelling devices can form biofilm, consequently cause severe morbidity and often fatal infections. Initial bacterial adhesion to the material surfaces is a complicated process that is affected by various physicochemical properties of both bacterial cells and substratum surfaces. The surface properties of the cells were characterized by the sessile drop technique. Moreover, the interfacial free energy of Staphylococcus aureus adhesion to the supporting materials was determined. The results showed that S. aureus examined at different pH levels could be considered hydrophilic. We noted hat the electron-donor character of S. aureus was important at intermediate pH (pH 5, pH 7, and pH 9) and it decreased at both limits acidic and basic conditions. In addition, the adhesion of Staphylococcus aureus ATCC 25923 to the hydrophilic glass and hydrophobic indium tin oxide (ITO)-coated glass surfaces at different pH values (2, 3, 5, 7, 9 and 11) was investigated using atomic force microscopy (AFM) and image analysis was assessed with the Mathlab^® program. The data analysis showed that cells (number of adhering cells to glass and ITO-coated glass surface) adhered strongly at acidic pH and weakly at alkaline pH. Also, S. aureus has the ability to attach to both hydrophobic and hydrophilic surfaces, but the adhesion was higher on hydrophobic surface.     

Adhesion of the Entomopathogenic Fungus Beauveria (Cordyceps) bassiana to Substrata

The entomopathogenic fungus Beauveria bassiana produces at least three distinct single-cell propagules, aerial conidia, vegetative cells termed blastospores, and submerged conidia, which can be isolated from agar plates, from rich broth liquid cultures, and under nutrient limitation conditions in submerged cultures, respectively. Fluorescently labeled fungal cells were used to quantify the kinetics of adhesion of these cell types to surfaces having various hydrophobic or hydrophilic properties. Aerial conidia adhered poorly to weakly polar surfaces and rapidly to both hydrophobic and hydrophilic surfaces but could be readily washed off the latter surfaces. In contrast, blastospores bound poorly to hydrophobic surfaces, forming small aggregates, bound rapidly to hydrophilic surfaces, and required a longer incubation time to bind to weakly polar surfaces than to hydrophilic surfaces. Submerged conidia displayed the broadest binding specificity, adhering to hydrophobic, weakly polar, and hydrophilic surfaces. The adhesion of the B. bassiana cell types also differed in sensitivity to glycosidase and protease treatments, pH, and addition of various carbohydrate competitors and detergents. The outer cell wall layer of aerial conidia contained sodium dodecyl sulfate-insoluble, trifluoroacetic acid-soluble proteins (presumably hydrophobins) that were not present on either blastospores or submerged conidia. The variations in the cell surface properties leading to the different adhesion qualities of B. bassiana aerial conidia, blastospores, and submerged conidia could lead to rational design decisions for improving the efficacy and possibly the specificity of entomopathogenic fungi for host targets.     

Adhesion of algal cells to surfaces

This paper reports the cell–substratum interactions of planktonic (Chlorella vulgaris) and benthic (Botryococcus sudeticus) freshwater green algae with hydrophilic (glass) and hydrophobic (indium tin oxide) substrata to determine the critical parameters controlling the adhesion of algal cells to surfaces. The surface properties of the algae and substrata were quantified by measuring contact angle, electrophoretic mobility, and streaming potential. Using these data, the cell–substratum interactions were modeled using thermodynamic, DLVO, and XDLVO approaches. Finally, the rate of attachment and the strength of adhesion of the algal cells were quantified using a parallel-plate flow chamber. The results indicated that (1) acid–base interactions played a critical role in the adhesion of algae, (2) the hydrophobic alga attached at a higher density and with a higher strength of adhesion on both substrata, and (3) the XDLVO model was the most accurate in predicting the density of cells and their strength of adhesion. These results can be used to select substrata to promote/inhibit the adhesion of algal cells to surfaces.     

The role of exopolymers in the attachment of sphingomonas paucimobilis

The importance of exopolymers in the adhesion of Sphingomonas paucimobilis was established by studying the attachment to glass of three mutants with defective gellan production. The attachment assays were performed in either phosphate buffered saline (controls) or in the exopolymeric solutions produced by the mutants. The exopolymer was found to have surface active properties, changing the glass surface from hydrophilic to hydrophobic, making adhesion thermodynamically favourable. Only the cells that had a substantial polymeric layer surrounding their walls were able to significantly colonise glass coated with the exopolymer. It is hypothesised that the exopolymer bound to the glass and the exopolymer present at the surface of the bacteria bound together, overcoming the energy barrier created by the negative charge of both surfaces. It is concluded that the exopolymer from S. paucimobilis has a dual role in the process of adhesion by both coating the surface thereby strengthening adhesion and by enhancing adhesion through the establishment of polymeric bridges.     

Influence of an S-layer on surface properties of Bacillus stearothermophilus

Various aspects of surface properties of the S-layer-carrying Bacillus stearothermophilus PV72 and of an S-layer-deficient mutant (strain PV72/T5) have been tested by adsorption assays on solid surfaces, electrostatic interaction chromatography and hydrophobic interaction chromatography. The adsorption assays have shown that cell adhesion of the S-layer-carrying strain was less influenced by environmental changes than it was with the S-layer-deficient mutant. Electrostatic interaction chromatography indicated that both strains have positively and negatively charged groups exposed on the cell surface but the S-layer-carrying strain reveals more positively charged groups than does the S-layer-deficient mutant. Hydrophobic interaction chromatography showed that both strains have a hydrophilic surface but that the hydrophilic properties are more pronounced with the strain lacking an S-layer.     

Listeria monocytogenes LO28: Surface Physicochemical Properties and Ability To Form Biofilms at Different Temperatures and Growth Phases

The surface physicochemical properties of Listeria monocytogenes LO28 under different conditions (temperature and growth phase) were determined by use of microelectrophoresis and microbial adhesion to solvents. The effect of these parameters on adhesion and biofilm formation by L. monocytogenes LO28 on hydrophilic (stainless steel) and hydrophobic (polytetrafluoroethylene [PTFE]) surfaces was assessed. The bacterial cells were always negatively charged and possessed hydrophilic surface properties, which were negatively correlated with growth temperature. The colonization of the two surfaces, monitored by scanning electron microscopy, epifluorescence microscopy, and cell enumeration, showed that the strain had a great capacity to colonize both surfaces whatever the incubation temperature. However, biofilm formation was faster on the hydrophilic substratum. After 5 days at 37 or 20°C, the biofilm structure was composed of aggregates with a three-dimensional shape, but significant detachment took place on PTFE at 37°C. At 8°C, only a bacterial monolayer was visible on stainless steel, while no growth was observed on PTFE. The growth phase of bacteria used to inoculate surfaces had a significant effect only in some cases during the first steps of biofilm formation. The surface physicochemical properties of the strain are correlated with adhesion and surface colonization.     

Quantifying the exploratory behaviour of Amphibalanus amphitrite cyprids

The behavioural response of cypris larvae from A. amphitrite (=Balanus amphitrite) exploring three model glass surfaces is quantified by close-range microscopy. Step length and step duration measurements reveal a response to both surface properties and flow. Without flow, 2-day-old cyprids took larger steps with shorter step duration on hydrophilic glass surfaces (bare and NH₂-treated) vs hydrophobic glass (CH₃-treated). These parameters suggest a more detailed, local inspection of hydrophobic surfaces and a more extensive exploration for hydrophilic surfaces. Cyprids under flow took longer steps and exhibited shorter probing times on hydrophobic glass. On hydrophilic glass, cyprids increased their step duration under flow. This active response is attributed to drag and lift forces challenging the cyprids' temporary anchoring to the substratum. Seven-day-old cyprids showed almost no discrimination between the model surfaces. Microscopic-scale observation of cyprid exploration is expected to provide new insights into interactions between cyprids and surfaces.     

Near‐neutral surface charge and hydrophilicity prevent mineral encrustation of Fe‐oxidizing micro‐organisms

Microbial survival in mineralizing environments depends on the ability to evade surface encrustation by minerals, which could obstruct nutrient uptake and waste output. Some organisms localize mineral precipitation away from the cell; however, cell surface properties – charge and hydrophobicity – must also play a role in preventing surface mineralization. This is especially relevant for iron‐oxidizing bacteria (FeOB), which face an encrustation threat from both biotic and abiotic mineralization. We used electron microscopy and surface characterization techniques to study the surfaces of two stalk‐forming neutrophilic FeOB: the marine Zetaproteobacterium Mariprofundus ferrooxydans PV‐1 and the recently isolated freshwater Betaproteobacterium Gallionellales strain R‐1. Both organisms lack detectable iron on cell surfaces. Live and azide‐inhibited M. ferrooxydans PV‐1 cells had small negative zeta potentials (?0.34 to ?2.73 mV), over the pH range 4.2–9.4; Gallionellales strain R‐1 cells exhibited an even smaller zeta potential (?0.10 to ?0.19 mV) over pH 4.2–8.8. Cells have hydrophilic surfaces, according to water contact angle measurements and microbial adhesion to hydrocarbons tests. Thermodynamic and extended Derjaguin–Landau–Verwey–Overbeek (XDLVO) calculations showed that as low charge causes low electrostatic attraction, hydrophilic repulsion dominates cell–mineral interactions. Therefore, we conclude that surface properties help enable these FeOB to survive in highly mineralizing environments. Given both mineral‐repelling surface properties and the ability to sequester Fe(III) biominerals in an organomineral stalk, these two FeOB have a well‐coordinated system to localize both biotic and abiotic mineral distribution.     

Dependence of the initial adhesion of biofilm forming Pseudomonas putida mt2 on physico-chemical material properties

Bacterial adhesion is strongly dependent on the physico-chemical properties of materials and plays a fundamental role in the development of a growing biofilm. Selected materials were characterized with respect to their physico-chemical surface properties. The different materials, glass and several polymer foils, showed a stepwise range of surface tensions (γ_s) between 10.3 and 44.7 mN m^?1. Measured zeta potential values were in the range between ?74.8 and ?28.3 mV. The initial bacterial adhesion parameter q _max was found to vary between 6.6 × 10⁶ and 28.1 × 10⁶ cm^?2. By correlation of the initial adhesions kinetic parameters with the surface tension data, the optimal conditions for the immobilization of Pseudomonas putida mt2 were found to be at a surface tension of 24.7 mN m^?1. Both higher and lower surface tensions lead to a smaller number of adherent cells per unit surface area. Higher energy surfaces, commonly termed hydrophilic, could constrain bacterial adhesion because of their more highly ordered water structure (exclusion zone) close to the surface. At low energy surfaces, commonly referred to as hydrophobic, cell adhesion is inhibited due to a thin, less dense zone (depletion layer or clathrate structure) close to the surface. Correlation of q _max with zeta potential results in a linear relationship. Since P. putida carries weak negative charges, a measurable repulsive effect can be assumed on negative surfaces.     

The role of bacterial surface and substratum hydrophobicity in adhesion ofLeptospira biflexa serovarpatoc 1 to inert surfaces

Adhesion of the hydrophilicLeptospira biflexa serovarpatoc 1 (L. patoc) was consistently greater on inert hydrophobic surfaces than on hydrophilic surfaces (glass and plastic). When inert substrata were coated with fetal calf serum (FCS) or bovine serum albumin fraction V (BSA), however, surface hydrophobicity was reduced compared to untreated surfaces, but adhesion ofL. patoc increased. The mechanism of adhesion at protein-coated surfaces is likely to be different than that at untreated surfaces, but it is suggested that the adhesion is nonspecific, as the level of adhesion is similar for different protein coatings. Increased adhesion to FCS- and BSA-coated surfaces was apparently not associated with substrate utilization (scavenging of fatty acids) from the coatings, as essentially fatty acid-free BSA-coated surfaces had similar levels of adhesion. The presence of FCS in the diluent lowered the adhesion ofL. patoc regardless of the original nature of the substratum. This may result from the mutual repulsion of the bacterium and the substratum caused by the exclusion volumes of similar macromolecules adsorbed to both surfaces from the FCS solution.