Bacterial Extracellular Polymeric Substances Research Articles

Relative Contribution of Biomolecules in Bacterial Extracellular Polymeric Substances to Disinfection Byproduct Formation

In this study, detailed chemical compositions of the biomolecules in extracellular polymeric substances (EPS) from both pure cultures of bacteria and mixed species biofilm isolated from a water utility were analyzed. Then, based on detailed EPS analysis results, the DBP yield experiments were conducted with both extracted EPS and surrogate chemicals to indirectly identify the influence of biomolecules and their structures on DBP formation and speciation. DBP yield results of both extracted EPS and EPS surrogates indicated that proteins in EPS have a greater influence on DBP formation, especially on the formation of nitrogenous DBPs (N-DBPs), where amino acids containing unsaturated organic carbon or conjugated bonds in R-group produced higher amount of DBPs. For regulated DBPs, HAA yields were higher than THM yields, while haloacetonitriles were the dominant DBP species formed among unregulated DBPs. However, DBP yields of polysaccharide monomers were lower than those of tested amino acids groups and the DBP yields of polysaccharide monomers were not significantly influenced by their structures. Considering the results obtained in this study, biofilm needs to be considered an important precursor to DBP formation and biofilm eradication methods for water distribution systems need to be carefully selected to minimize subsequent DBP formation.

The roles of extracellularDNAin the structural integrity of extracellular polymeric substance and bacterial biofilm development

Bacteria adhere to natural and engineered surfaces and develop into mature biofilms encased in self-produced extracellular polymeric substances (EPSs). EPS consists of polysaccharides, proteins, metabolites and extracellular DNA (eDNA). Extracellular DNA release by bacteria is mediated by both quorum-sensing (QS)-dependent and -independent mechanisms. Quorum-sensing-independent mechanisms are responsible for basal levels of eDNA release, whereas QS-dependent mechanisms control the production of prophages, phenazines and proteins involved in cell lysis and subsequent release of elevated amounts of eDNA. Extracellular DNA binds with other biopolymers such as polysaccharides, proteins or metabolites like phenazines, thereby providing structural integrity to EPS. Extracellular DNA promotes attractive acid-base interactions between bacterial cells and between bacteria and surfaces. It therefore plays an essential structural role in stabilising biofilms and protecting bacterial cells from physical and chemical challenges. Accordingly, with current knowledge, it becomes clear that targeting and destroying eDNA in bacterial EPS is a promising strategy for treatment of bacterial-associated infections in a medical context and biofilm control on surfaces to prevent biocorrison in an engineering context. In contrast, the addition of DNA can be applied to engineering of biofilms for beneficial purposes such as remediation of environmental pollutants and electricity or fuel production in bioelectrochemical systems or bioreactors.

Effects of Biological Molecules on Calcium Mineral Formation Associated with Wastewater Desalination as Assessed using Small-Angle Neutron Scattering

Calcium phosphate scale formation on reverse osmosis (RO) membranes is one of the main limitations on cost-effective desalination of domestic wastewater worldwide. It has been shown that organic agents affect mineralization. In this study, we explored mineralization in the presence of two biofilm-relevant organic compounds, the proteins bovine serum albumin (BSA) and lysozyme, in a simulated secondary effluent (SSE) solution using small-angle neutron scattering (SANS), and applied the results to analyses of mineral precipitation in RO desalination of secondary effluents of wastewater. The two proteins are prominent members of bacterial extracellular polymeric substances (EPSs), forming biofilms that are frequently associated with RO-membrane fouling during wastewater desalination. Laboratory experiments showed that both proteins in SSE solution are involved in complex mineralization processes. Only small portions of both protein fractions are involved in mineralization processes, whereas most of the protein fractions remain as monomers in solution. Contrast variation showed that composite particles of mineral and protein are formed instantaneously to a radius of gyration of about 300 Å, coexisting with particles of about μm size. After about one day, these large particles start to grow again at the expense of the 300 Å particles. The volume fraction of the 300 Å particles is of the order of 2 × 10(-4), which is too large to represent calcium phosphate such as hydroxyapatite as the only mineral present. Considering the data of mineral volume fraction obtained here as well as the solubility product of possible mineral polymorphs in the SSE solution, we suggest the formation of protein-mineral particles of hydroxyapatite and calcium carbonate during scale formation.

Carbohydrate analysis by methanolysis method and application to compositional analysis of transparent exopolymer particles

Measurement of uronic acids (URAs) which are a group of acidic sugar, would be useful for the understanding of dynamics of bacterial extracellular polymeric substances (EPS) in marine environments. However, the URA analysis using traditional hydrolysis method which is used for neutral sugar analysis poses serious problems in URA that is unstable under hydrolysis. We developed the methanolysis method, which deploymerizes polysaccharides while retaining quantitative information. Our method was applied to coastal seawater, and the URAs distribution was compared with that of transparent exopolymer particles (TEP) which are acidic sugar containing particles. Since the relationship of URA with TEP was relatively weak, URA-containing polysaccharides present in bacterial EPS would not participate as a structural component of TEP.

Bacterial extracellular polymeric substances and their effect on settlement of zoospore of Ulva fasciata

The extracellular polymeric substances (EPSs) secreted by Bacillus flexus (GU592213) were estimated to have the molecular weight of approximately 1528 and 33,686kDa with the elemental composition of Na, P, Mg, C, O, Cl and S. The 1H NMR and FT-IR analysis of EPS confirmed the presence of different aliphatic and aromatic groups. The EPS was amorphous in nature with an average particle size of 13.969μm (d 0.5) and roughness of 193nm. The GC–MS analysis has revealed different monosaccharides such as fucose, ribose, xylose, galactose, mannose and glucose. Oligo and polysaccharides were detected with MALDI TOF–TOF MS. The bacterial EPS for the first time tested as a natural substratum for settle of zoospores of Ulva fasciata by incubating for various durations ranging from 2h to 48h. The zoospore settlement on EPS coated cover slips progressively increased with incubation time in axenic cultures over controls. The EPS, thus investigated in this study was found to facilitate the primary settlement of spores that play crucial role in recruitment of macroalgal communities in coastal environment including intertidal regions.

Influence of Bacterial Extracellular Polymeric Substances on the Formation of Carbonaceous and Nitrogenous Disinfection Byproducts

Considering the regulatory presence of residual chlorine in water distribution systems, untreated organic matter may not be the sole contributor to disinfection byproduct (DBP) formation, given the presence of microbial biofilm with extracellular polymeric substances (EPS). This study investigated the influence of bacterial EPS on the formation of carbonaceous DBPs (C-DBPs) and nitrogenous DBPs (N-DBPs), reacting chlorine with Pseudomonas strains that produce different quantities and composition of EPS. When biomass is reacted in excess to chlorine, both C-DBPs and N-DBPs were produced without preference for speciation. However, under an excess of chlorine compared to biomass, increased EPS content led to enhanced formation of DBPs. The DBP yield of haloacetic acids (HAAs) was higher than that of trihalomethanes where dichloroacetic acid was dominant in HAA species. Additionally, chemical composition of EPS influenced the yields of DBPs. The N-DBP yield from P. putida EPS was two times higher than that of P. aeruginosa EPS, which suggested that higher organic nitrogen content in EPS contributes to higher N-DBP yield. Moreover, time-based experiments revealed that DBP formation from biomass occurs rapidly, reaching a maximum in less than four hours. Combined results suggest that bacterial EPS have significant roles in both the formation and fate of DBPs.

Arsenic adsorption by Bacterial Extracellular Polymeric Substances

The main objective of this work was to isolate arsenic resistant bacteria from contaminated soil, followed by screening for their ability to adsorb arsenic. Six bacterial isolates (S1 to S6) were obtained from arsenic contaminated soil samples and among these, five (S1, S2, S3, S5 and S6) were characterized as bacillus and the rest one (S4) was cocci depending on shape. All the isolates except S6 produced extracellular polymeric substances (EPS) in the culture medium and displayed arsenic adsorbing activities demonstrated by adsorption of around 90% from initial concentration of 1 mg/L sodium arsenite. To clarify the role of EPS, we killed the bacteria that produced EPS and used these killed bacteria to see whether they could still adsorb arsenic or not. We found that they could adsorb arsenic similarly like that of EPS produced live bacterial isolates. From the observation it is concluded that these isolates showed potentiality to adsorb arsenic and hence might be used for bioremediation of arsenic. DOI: http://dx.doi.org/10.3329/bjm.v28i2.11821 Bangladesh J Microbiol, Volume 28, Number 2, December 2011, pp 80-83

Membrane bioreactor: TMP rise and characterization of bio-cake structure using CLSM-image analysis

Abstract Membrane biofouling in membrane bioreactor (MBR) was analyzed quantitatively using a quantitative image analysis technique combined with confocal laser scanning microscopy (CLSM). The CLSM-Image analysis technique was (i) used to quantify the structure of bio-cake relating to the spatial change in the architecture, (ii) then applied to calculate the contribution of bacterial cell and extra-cellular polymeric substances (EPSs) to bio-cake resistances (Rc). A variation in the structural parameters of the bio-cake was found for different fluxes. EPS was more prevalent for the system operated under the lowest flux of 13 L/(m2 h). At this “subcritical” flux, the amount of EPS in the final bio-cake was greater than the amount of bacterial cells. This flux also gave the greatest rate of resistance rise towards the end of the period of operation. The profiles of each component (cell and EPSs) within the bio-cake were used to estimate the cake resistance (Rc). A particle size of less than 1 μm was required to have correspondence between theory and measurement. It was deduced that the steep TMP rise (labeled by others as Stage 3) is due to a combination of two mechanisms: inhomogeneous pore loss and changes in percolation due to EPS accumulation.

A new approach to study local corrosion processes on steel surfaces by combining different microscopic techniques

Corrosion studies of materials on the micro or even nano-scale level are cumbersome due to instrumental limitations and handling procedures. If biological processes are involved the spatial resolution is even more important and sample preparation is usually the limitation. Attachment of bacteria on stainless steel surface is a complex interfacial process including interactions of bacterial cells and bacterial extracellular polymeric substances with the surface. To overcome the limitations in sample preparations and resolution we present a new stainless steel sample holder to switch among epifluorescent microscope (EFM), AFM and SEM at exactly the same position. Exemplary bacterial accumulation was studied by staining the bacterial DNA with a fluorescent dye over time. It was possible to distinguish among bacteria and other surface characteristic such as deformations or grain structures. Also surface topographic features such as roughness at the grain boundaries and deposits were quantified. All three techniques complement one another in the way that AFM is a high-resolution technique that does not allow to distinguish directly bacterial cell structures, whereas EFM offers excellent bacterial identification based on staining at a low resolution that can complement AFM images. Application of SEM in the last step will reveal inclusions and grain structure and combined with EDX gives the composition of the substrate, inclusions and corrosion deposit. The combination of the three high-resolution techniques enables a more detailed understanding of surface phenomena. The method itself is quite elegant and easy to handle which is an important aspect in materials research, especially when a high sample throughput is needed.

Selection of effective methods for extracting extracellular polymeric substances (EPSs) from Bacillus megaterium TF10

Bacterial extracellular polymeric substances (EPSs) play an important role in the formation and stabilization of bioaggregates, such as biofilm, microbial flocs and granules. Thus, the selection of appropriate extraction method is of critical importance, which may affect the yield, compositions and properties of EPS. In this work, six different methods used for EPS extraction, including ultrasonication, heating, formaldehyde+NaOH, H2SO4, glutaraldehyde, and EDTA methods, from Bacillus megaterium TF10, a bacterium with a high EPS-producing capacity isolated from a soil sample, are investigated. These EPS extraction methods are compared in terms of EPS yields and compositions, cell lysis, and flocculation activities and spectrum characteristics of extracted EPS. The results show that both EPS yield and cell lysis generally increase with the extraction time. The heating, formaldehyde+NaOH and H2SO4 methods lead to a high EPS yield compared to the ultrasonication or EDTA methods, while the ultrasonication and H2SO4 methods cause much more cell lysis than the formaldehyde+NaOH treatment. The flocculation activities of EPS, which can quantitatively reflect the EPS disruption during extraction, are also evaluated. The flocculation efficiencies of the extracted EPS are found in the order of: formaldehyde+NaOH (30-min formaldehyde treatment and then 60-min NaOH treatment), 92.4%>EDTA (10h), 92.2%>heating (120min), 91.6%>glutaraldehyde (15min), 90.9%>ultrasonication (30min), 81.0%>H2SO4 (45min), 73.2%>control, 59.9%. The IR and EEM spectra suggest that the EPS compositions and structures also vary significantly with the extraction method. Among the six methods, the EDTA method with an extraction time of 10h was identified to be most effective method to extract EPS from B. megaterium TF10.

Impact of cranberry juice on initial adhesion of the EPS producing bacterium Burkholderia cepacia

The impact of cranberry juice was investigated with respect to the initial adhesion of three isogenic strains of the bacterium Burkholderia cepacia with different extracellular polymeric substance (EPS) producing capacities, viz. a wild-type cepacian EPS producer PC184 and its mutant strains PC184rml with reduced EPS production and PC184bceK with a deficiency in EPS production. Adhesion experiments conducted in a parallel-plate flow chamber demonstrated that, in the absence of cranberry juice, strain PC184 had a significantly higher adhesive capacity compared to the mutant strains. In the presence of cranberry juice, the adhesive capacity of the EPS-producing strain PC184 was largely reduced, while cranberry juice had little impact on the adhesion behavior of either mutant strain. Thermodynamic modeling supported the results from adhesion experiments. Surface force apparatus (SFA) and scanning electron microscope (SEM) studies demonstrated a strong association between cranberry juice components and bacterial EPS. It was concluded that cranberry juice components could impact bacterial initial adhesion by adhering to the EPS and impairing the adhesive capacity of the cells, which provides an insight into the development of novel treatment strategies to block the biofilm formation associated with bacterial infection.

Membrane biofouling and scaling in forward osmosis membrane bioreactor

The forward osmosis membrane bioreactor (FOMBR) has received much attention recently. Due to the high rejection nature of FO membranes, the biomass, dissolved organic and inorganic compounds retained in the bioreactor could cause membrane fouling by multiple mechanisms. In this study, a 45% permeate flux decrease was observed in a well controlled FOMBR equipped with a submerged hollow fiber FO membrane module with the active layer facing the draw solution (AL-DS) configuration. A series of characterizations were performed to explore membrane fouling mechanisms in the FOMBR. It was found that a biofouling layer covered the substrate surface of the FO membrane with a combined structure of bacterial clusters and extracellular polymeric substances (EPS), which contributed to 72% drop of the membrane mass transfer coefficient (Km) and around 10% increase in the hydraulic resistance. The inorganic fouling was caused by Ca, Mg, Al, Si, Fe and P that contributed 60% of the total hydraulic resistance of the fouled membrane and decreased the Km by around 34%. These results suggest that in this application the FO fouling is governed by the coupled influences of biofilm formation and inorganic scaling. When the configuration was reversed with the active layer facing the feed solution (AL-FS), a negligible flux decline was obtained by applying intermittent tap water flushing to the membrane surface, which suggests that the AL-FS orientation is favorable for FOMBR operation. An effective strategy for fouling control is to prevent internal scaling and the over-growth of biofilm on the membrane surface.

Post-glacial microbialite formation in coral reefs of the Pacific, Atlantic, and Indian Oceans

The occurrence of microbialites in post-glacial coral reefs has been interpreted to reflect an ecosystem response to environmental change. The greater thickness of microbialites in reefs with a volcanic hinterland compared to thinner microbial crusts in reefs with a non-volcanic hinterland led to the suggestion that fertilization of the reefal environment by chemical weathering of volcanic rocks stimulated primary productivity and microbialite formation. Using a molecular and isotopic approach on reef-microbialites from Tahiti (Pacific Ocean), it was recently shown that sulfate-reducing bacteria favored the formation of microbial carbonates. To test if similar mechanisms induced microbialite formation in other reefs as well, the Tahitian microbialites are compared with similar microbialites from coral reefs off Vanuatu (Pacific Ocean), Belize (Caribbean Sea, Atlantic Ocean), and the Maldives (Indian Ocean) in this study. The selected study sites cover a wide range of geological settings, reflecting variable input and composition of detritus. The new lipid biomarker data and stable sulfur isotope results confirm that sulfate-reducing bacteria played an intrinsic role in the precipitation of microbial carbonate at all study sites, irrespective of the geological setting. Abundant biomarkers indicative of sulfate reducers include a variety of terminally-branched and mid chain-branched fatty acids as well as mono-O-alkyl glycerol ethers. Isotope evidence for bacterial sulfate reduction is represented by low δ34S values of pyrite (−43 to −42‰) enclosed in the microbialites and, compared to seawater sulfate, slightly elevated δ34S and δ18O values of carbonate-associated sulfate (21.9 to 22.2‰ and 11.3 to 12.4‰, respectively). Microbialite formation took place in anoxic micro-environments, which presumably developed through the fertilization of the reef environment and the resultant accumulation of organic matter including bacterial extracellular polymeric substances (EPS), coral mucus, and marine snow in cavities within the coral framework. ToF-SIMS analysis reveals that the dark layers of laminated microbialites are enriched in carbohydrates, which are common constituents of EPS and coral mucus. These results support the hypothesis that bacterial degradation of EPS and coral mucus within microbial mats favored carbonate precipitation. Because reefal microbialites formed by similar processes in very different geological settings, this comparative study suggests that a volcanic hinterland is not required for microbialite growth. Yet, detrital input derived from the weathering of volcanic rocks appears to be a natural fertilizer, being conductive for the growth of microbial mats, which fosters the development of particularly abundant and thick microbial crusts.

Transport Behavior of Selected Nanoparticles with different Surface Coatings in Granular Porous Media coated with Pseudomonas aeruginosa Biofilm

Well-controlled laboratory column experiments were conducted to understand the influence of Pseudomonas aeruginosa (P. aeruginosa) biofilms on the transport of selected engineered nanoparticles (ENPs) in granular porous media representative of groundwater aquifers or riverbank filtration settings. To understand the importance of particle size on retention in the biofilm-coated granular (quartz sand) matrix, column experiments were carried out using nanosized (20 nm) and micrometer-sized (1 μm) sulfate-functionalized polystyrene latex particles (designated as 20 nSL and 1 mSL, respectively). Additional experiments conducted with nanosized (20 nm) carboxyl-modified latex particles (20nCL) and carboxyl-modified CdSe/ZnS quantum dots (QDs) provide information on the influence of particle surface chemistry on retention. Biofilm grown on the surface of the sand was characterized by total biomass quantification, confocal laser scanning microscopy (CLSM), and electrokinetic analysis. All four particles exhibit increased retention in the biofilm-coated packed bed: e.g., the attachment efficiency (α) of the 1 mSL particle increases from 0.40 to 1.7, whereas α for the 20 nSL particle increases from 0.04 to 0.10 in the biofilm-coated system. Particle surface chemistry can also influence the affinity of the ENPs for the biofilm coating as revealed by the greater attachment of the 20 nSL particle onto the biofilm-coated sand (α = 0.10) than its carboxylated counterpart (α = 0.04). Column experiments conducted using sand coated with growth medium (LB) or extracellular polymeric substances (EPS) extracted from P. aeruginosa biofilms further reveal that particle surface chemistry influences the interaction between the different ENPs and these coated sand surfaces. Namely, coating of sand surfaces with LB medium or bacterial EPS does not affect the transport of the sulfonated nanoparticle, but the LB coating leads to decreased retention of the carboxylated latex nanoparticle. Furthermore, our results show that EPS coatings are not necessarily good surrogates for biofilm-coated sand. Electrokinetic characterization of the clean and coated sand surfaces also reveals that the extent of particle retention is not controlled by electrical double layer interactions. Future studies should thus be aimed at improving our understanding of the fundamental mechanisms (both colloidal and noncolloidal) governing nanoparticle transport and fate in biofilm-laden granular aquatic environments.

Role of Bacterial Biomass in the Sorption of Ni by Biomass-Birnessite Assemblages

Birnessites precipitated by bacteria are typically poorly crystalline Mn(IV) oxides enmeshed within biofilms to form complex biomass-birnessite assemblages. The strong sorption affinity of bacteriogenic birnessites for environmentally important trace metals is relatively well understood mechanistically, but the role of bacterial cells and extracellular polymeric substances appears to vary among trace metals. To assess the role of biomass definitively, comparison between metal sorption by biomass at high metal loadings in the presence and absence of birnessite is required. We investigated the biomass effect on Ni sorption through laboratory experiments utilizing the birnessite produced by the model bacterium, Pseudomonas putida. Surface excess measurements at pH 6-8 showed that birnessite significantly enhanced Ni sorption at high loadings (up to nearly 4-fold) relative to biomass alone. This apparent large difference in affinity for Ni between the organic and mineral components was confirmed by extended X-ray absorption fine structure spectroscopy, which revealed preferential Ni binding to birnessite cation vacancy sites. At pH ≥ 7, Ni sorption involved both adsorption and precipitation reactions. Our results thus support the view that the biofilm does not block reactive mineral surface sites; instead, the organic material contributes to metal sorption once high-affinity sites on the mineral are saturated.

Assessing the Importance of Organic Matrix Materials in Biofilm Chemical Reactivity: Insights from Proton and Cadmium Adsorption onto the Commercially Available Biopolymer Alginate

Biofilms coat the exterior of most water-exposed interfaces, from the surfaces of sediments and rocks to the interior walls of fluid transport systems and even medical and dental apparatus. Composed of a diverse assemblage of microbial species growing in a matrix of extracellular polymeric substances (EPS), biofilms are well-known for their ability to sorb metals and nucleate mineral phases. In this study, purified alginate, a major polysaccharide component of some algal and bacterial EPS, was studied to ascertain its chemical reactivity towards dissolved cadmium and protons, and thus better constrain its role in overall EPS reactivity. FTIR analysis and compositional constraints based on known molecular structure indicate that alginate’s geochemical behaviour is dominated by a single carboxyl functional group. Correspondingly, potentiometric titration data were best fit using a single functional group acidity constant (pKa) and site concentration of 3.98 ± 0.01 and 1.728 ± 0.02 mol/kg, respectively, which are in agreement with typical carboxyl acidity (pKa 3–6) and carboxyl functional group concentration based on alginate polymer composition. The logarithm of the Cd-carboxyl complexation constant (log K) was determined to be −0.52 ± 0.22, lower than carboxyl-Cd stability constants reported from independent studies of isolated microbes. Together, these results place important constraints on organic matrix contributions to overall biofilm reactivity.

Contribution of quorum sensing to the virulence of Pseudomonas aeruginosa in pressure ulcer infection in rats

The impact of quorum sensing (QS) in in vivo models of infection has been widely investigated, but there are no descriptions for ischemic wound infection. To explore the role of QS in Pseudomonas aeruginosa in the establishment of ischemic wound infection, we challenged a pressure ulcer model in rats with the PAO-1, PAO-1 derivatives ΔlasIΔrhlI and ΔlasRΔrhlR strains, which cannot induce the virulence factor under QS control, thus the reduced tissue destruction was expended in these mutant strains. However unexpectedly, on postwounding day 3, the inflammatory responses in the three groups were similarly severe and the numbers of bacteria in tissue samples did not differ among the three strains. Biofilm formation was immature in QS-deficient strains, defined by the absence of dense bacterial aggregates and extracellular polymeric substance, which was confirmed by scanning electron microscopy. The Pseudomonas aeruginosa QS signal, acylated homoserine lactone, was only quantified from wound samples in the PAO-1 group. The swimming and twitching motilities were significantly enhanced in the ΔlasRΔrhlR group compared with the PAO-1 group in vitro. A significantly larger wound area was correlated with the bacterial motility. The inflammation in the early phase of bacterial challenge to wounds with immature biofilm formation in the QS-deficient strains indicated that the role of QS was more crucial for the chronic phase than for the acute phase of infection. The present findings indicate a difference in the importance of QS in ischemic wound infections compared with other infection models.

Composition and molar mass characterisation of bacterial extracellular polymeric substances by using chemical, spectroscopic and fractionation techniques

Environmental contextExtracellular polymeric substances (EPS) released by microorganisms are an important component of organic matter in the environment. EPS play an essential role in cell adhesion to surfaces, biofilm and floc formation, soil aggregation and stability and in the activated sludge of waste water treatment plants. EPS are complex mixtures containing components of different chemical nature and molecular size, which make their characterisation difficult. The present work explores the link between chemical composition and molar-mass distribution of the EPS released by the bacterium Sinorhizobium meliloti by using a combination of chemical, spectroscopic and fractionation techniques. AbstractThe chemical composition and molar-mass distribution of extracellular polymeric substances (EPS) produced by the bacterium Sinorhizobium meliloti have been characterised by combining asymmetrical flow field-flow fractionation (AFlFFF), chemical and spectroscopic techniques. The relationship between the EPS composition and molar-mass distribution has been studied by comparing the characteristics of EPS excreted by the wild type S. meliloti and by a mutant deficient in the production of high-molar-mass EPS, as well as by the analysis of total protein content in the collected AFlFFF fractions. Total organic carbon, protein and polysaccharide contents of the EPS were also determined. Obtained results demonstrate the existence of two major populations with weight-average molar masses of 1.40 × 105 and 4.57 × 105 g mol–1 respectively. The lower molar-mass population contained predominantly protein-like substances, detectable by UV-VIS spectroscopy, whereas the higher molar-mass population was rich in exopolysaccharides and exoproteins. These findings are in general agreement with the size distributions and chemical heterogeneity observed by nanoparticle tracking analysis, and the characterisation of the composition of all the EPS by different analytical techniques.

Plasma-Enhanced Synthesis of Bioactive Polymeric Coatings from Monoterpene Alcohols: A Combined Experimental and Theoretical Study

This paper describes the synthesis and characterization of a novel organic polymer coating for the prevention of the growth of Pseudomonas aeruginosa on the solid surface of three-dimensional objects. Substrata were encapsulated with polyterpenol thin films prepared from terpinen-4-ol using radio frequency plasma enhanced chemical vapor deposition. Terpinen-4-ol is a constituent of tea tree oil with known antibacterial properties. The influence of deposition power on the chemical structure, surface composition, and ultimately the antibacterial inhibitory activity of the resulting polyterpenol thin films was studied using X-ray photoelectron spectroscopy (XPS), water contact angle measurement, atomic force microscopy (AFM), and 3-D interactive visualization and statistical approximation of the topographic profiles. The experimental results were consistent with those predicted by molecular simulations. The extent of bacterial attachment and extracellular polymeric substances (EPS) production was analyzed using scanning electron microscopy (SEM) and confocal scanning laser microscopy (CSLM). Polyterpenol films deposited at lower power were particularly effective against P. aeruginosa due to the preservation of original terpinen-4-ol molecules in the film structure. The proposed antimicrobial and antifouling coating can be potentially integrated into medical and other clinically relevant devices to prevent bacterial growth and to minimize bacteria-associated adverse host responses.

Mechanism of bioleaching chalcopyrite by Acidithiobacillus ferrooxidans in agar-simulated extracellular polymeric substances media

The mechanism of leaching chalcopyrite by Acidithiobacillus ferrooxidans (A. ferrooxidans) in agar-simulated extracellular polymeric substances (EPS) media was investigated. The results indicate that bacterial EPS can release H+ and concentrate Fe3+; Fe2+ is movable between agar-simulated EPS phase and bulk solution phase, but it is difficult for Fe3+ to move due to its hydroxylation and EPS complex action; A. ferrooxidans first prefer Fe2+ as energy to metabolize compared with chalcopyrite, and a suitable simulated EPS environment for bacterial living is at about pH 1.8; the iron precipitates and jarosites formed by a lot of biologically oxidized Fe3+ cover the simulated EPS easily and form an impermeable deposit acting as a limited barrier of ion transport that attenuates the aggressiveness of the bioleaching attack. The EPS layer blocked by iron precipitates or jarosites is responsible for the chalcopyrite passivation.