Enhanced Biofilm Growth Research Articles

Enhancing biofilm growth in an integrated fixed-film activated sludge process through modification of polypropylene carriers

Biofilm is crucial in implementing integrated fixed-film activated sludge (IFAS) systems. However, current carriers face challenges in long-term stable operations. This study proposes using cationic polyacrylamide (PAM) as a positive-charged addictive and surface abrasion to modify polypropylene (PP) pipes to enhance biofilm growth and maintain long-time operation in IFAS applications. The modified PP carriers have significantly increased specific surface area compared to unmodified ones. The growth of biofilm on modified carriers is as much as over four times due to the improved biocompatibility of the material. The follow-up aerobic IFAS process achieves over 40% total nitrogen (TN) removal through simultaneous nitrification and denitrification with no specific anoxic stages or reactors. The sludge settling performance of the system is also improved with a stable 30-min sludge settling ratio of 18%. The maximum specific denitrification rate of the detached biofilm is 17.82 mg NO3−-N/g MLVSS/h, which is 33% higher than the pure activated sludge system. The high-throughput sequencing analysis results reveal that the abundance of biofilm-formation beneficial microbes increased from 0.02% to 16.47%.

Enhanced Bacterial Growth by Polyelemental Glycerolate Particles.

While polyelemental alloys are shown to be promising for healthcare applications, their effectiveness in promoting bacterial growth remains unexplored. In the present work, we evaluated the interaction of polyelemental glycerolate particles (PGPs) with Escherichia coli (E. coli) bacteria. PGPs were synthesized using the solvothermal route, and nanoscale random distribution of metal cations in the glycerol matrix of PGPs was confirmed. We observed 7-fold growth of E. coli bacteria upon 4 h of interaction with quinary glycerolate (NiZnMnMgSr-Gly) particles in comparison to control E. coli bacteria. Nanoscale microscopic studies on bacteria interactions with PGPs showed the release of metal cations in the bacterium cytoplasm from PGPs. The electron microscopy imaging and chemical mapping indicated bacterial biofilm formation on PGPs without causing significant cell membrane damage. The data showed that the presence of glycerol in PGPs is effective in controlling the release of metal cations, thus preventing bacterial toxicity. The presence of multiple metal cations is expected to provide synergistic effects of nutrients needed for bacterial growth. The present work provides key microscopic insights of mechanisms by which PGPs enhance biofilm growth. This study opens the door for future applications of PGPs in areas where bacterial growth is essential including healthcare, clean energy, and the food industry.

Microalgal extract as bio-coating to enhance biofilm growth of marine microalgae on microporous membranes

Microalgal biofilm is a popular platform for algal production, nutrient removal and carbon capture; however, it suffers from significant biofilm exfoliation under shear force exposure. Hence, a biologically-safe coating made up of algal extracellular polymeric substances (EPS) was utilized to secure the biofilm cell retention and cell loading on commercial microporous membrane (polyvinylidene fluoride), making the surfaces more hydrophobic (contact angle increase up to 12°). Results demonstrated that initial cell adhesion of three marine microalgae (Amphora coffeaeformis, Cylindrotheca fusiformis and Navicula incerta) was enhanced by at least 1.3 times higher than that of pristine control within only seven days with minimized biofilm exfoliation issue due to uniform distribution of sticky transparent exopolymer particles. Bounded extracellular polysaccharide gathered was approximately 23% higher on EPS-coated membranes to improve the biofilm's hydraulic resistance, whereas bounded extracellular protein would only be substantially elevated after the attached cells re-accommodate themselves onto the EPS pre-coating of themselves. In accounting the rises of hydrophobic protein content, biofilm was believed to be more stabilized, presumably via hydrophobic interactions. EPS biocoating would generate a groundswell of interest for bioprocess intensifications though there are lots of inherent technical and molecular challenges to be further investigated in future.

Rapid adaptation of a complex trait during experimental evolution of Mycobacterium tuberculosis.

Tuberculosis (TB), caused by Mycobacterium tuberculosis (M. tb), is a leading cause of death due to infectious disease. TB is not traditionally associated with biofilms, but M. tb biofilms are linked with drug and immune tolerance and there is increasing recognition of their contribution to the recalcitrance of TB infections. Here, we used M. tb experimental evolution to investigate this complex phenotype and identify candidate loci controlling biofilm formation. We identified novel candidate loci, adding to our understanding of the genetic architecture underlying M. tb biofilm development. Under selective pressure to grow as a biofilm, regulatory mutations rapidly swept to fixation and were associated with changes in multiple traits, including extracellular matrix production, cell size, and growth rate. Genetic and phenotypic paths to enhanced biofilm growth varied according to the genetic background of the parent strain, suggesting that epistatic interactions are important in M. tb adaptation to changing environments.

Role of Simulated Body Fluid in Biofilm Formation and Growth on a Polycarbonate Material

Bacteria form biofilms to facilitate colonization, and biofilm formation on polymeric medical devices is a common cause of hospital-acquired infection. Simulated body fluid (SBF) is a supersaturated calcium-phosphate solution with ionic composition nearly equal to that of human blood plasma, and has been used to test the bioactivity of materials. The purpose of this work was to understand whether SBF influenced surface structure on bacterial adhesion and biofilm formation on polycarbonate, a polymer commonly used in medical devices. In this study, polycarbonate coupons were immersed in a SBF solution at 37 oC for 7 and 14 days and air-dried for 30 minutes, and compared with deionized water immersion. Colony biofilms of P. aeruginosa were then investigated by growing bacteria on top surface of immersed coupons for 24 and 48 hours, and observed by the quantitative assay (areal cell density) and visualized using a field emission scanning electron microscopy (FESEM). Results stated that a prolonged immersion time of coupons in deionized water enhanced biofilm growth. Immersion in SBF for a period of 14 days showed a significant reduction in the viability following 24 hours of incubation compared to that in deionized water incubated for 48 hours. FESEM further demonstrated that P. aeruginosa had a tendency to form biofilm on a polycarbonate substrate, and was able to develop biofilms on both the SBF and deionized water. Significant cell clusters and bacterial adhesion was observed at 48-hour incubation. These insights can potentially assist in the establishment of infection and colonization of this opportunistic pathogen, and will aid the development of strategies to prevent biofilm formation.

Temperature induced amyloid production, biofilm formation and fitness in marine Bacillus sp.

Biofilm development in industrial cooling systems is influenced by the prevailing environmental conditions. However, the impact of temperature rise, common to industrial cooling systems, on biofilms is unclear. Here, the effect of temperature increase on biofilm formation and the extracellular polymeric substances (EPSs) production in marine biofilm forming Bacillus species thriving in the cooling water system of an operating power plant was investigated. Experimental data showed that biofilm formation in Bacillus sp. was significantly increased by up to 90% at 37–45 °C as compared to ambient seawater temperature of 30 °C. Enhanced biofilm growth at 37 °C and above was found to be associated with increased production of EPSs. Biofilm growth and EPSs production were increased by 47% and 62%, respectively, at 45 °C as compared to at 30 °C. Detailed analysis indicated that production of amyloid, important structural EPSs in the Bacillus biofilms, was positively correlated with an increase in incubation temperature. Amyloid production in turn altered the characteristics of Bacillus colony biofilms including morphology, roughness and wetting behaviour, thus facilitating fitness at higher temperatures. Biofilm formation and amyloid production are likely important physiological determinants for survival strategies of Bacillus persistence in the warm environmental settings of seawater cooling system.

Flow shear stress applied in self-buffered microbial fuel cells

The development of renewable and clean energy has been the priority of the global research field due to the urgent effects of climate change. Microbial fuel cell (MFC) is recognized as a sustainable approach to simultaneously generate power and treat wastewater through the employment of microorganisms as catalyst. The use of buffer solution in the wastewater treatment makes the commercial application of MFCs challenging due to their environmental impact and high costs. This work uses rotational motion to generate the flow stress in the anode chamber of the MFCs to enhance biofilm growth and mass transfer that leads to an overall performance improvement of the system. The effects on pH, chemical oxygen demand (COD), and power density were evaluated under rotational speeds of the magnetic stirrer from 0 to 640 rpm. The influence of the stirrer was then assessed utilizing the same parameters specified for scenarios with and without buffer. The results reveal that at 480 rpm of stirring speed, the pH value was neutral with a maximum COD removal of 82 % for bufferless and 93 % for buffered scenarios. In addition, for bufferless operation at 480 rpm yielded a power density of 402 mWm−2. The results of the flow stress analysis for bufferless and buffered MFCs are beneficial for the commercialization and future development of the system for wastewater treatment applications.

Enterococcus faecalis Manganese Exporter MntE Alleviates Manganese Toxicity and Is Required for Mouse Gastrointestinal Colonization.

Bacterial pathogens encounter a variety of nutritional environments in the human host, including nutrient metal restriction and overload. Uptake of manganese (Mn) is essential for Enterococcus faecalis growth and virulence; however, it is not known how this organism prevents Mn toxicity. In this study, we examine the role of the highly conserved MntE transporter in E. faecalis Mn homeostasis and virulence. We show that inactivation of mntE results in growth restriction in the presence of excess Mn, but not other metals, demonstrating its specific role in Mn detoxification. Upon growth in the presence of excess Mn, an mntE mutant accumulates intracellular Mn, iron (Fe), and magnesium (Mg), supporting a role for MntE in Mn and Fe export and a role for Mg in offsetting Mn toxicity. Growth of the mntE mutant in excess Fe also results in increased levels of intracellular Fe, but not Mn or Mg, providing further support for MntE in Fe efflux. Inactivation of mntE in the presence of excess iron also results in the upregulation of glycerol catabolic genes and enhanced biofilm growth, and addition of glycerol is sufficient to augment biofilm growth for both the mntE mutant and its wild-type parental strain, demonstrating that glycerol availability significantly enhances biofilm formation. Finally, we show that mntE contributes to colonization of the antibiotic-treated mouse gastrointestinal (GI) tract, suggesting that E. faecalis encounters excess Mn in this niche. Collectively, these findings demonstrate that the manganese exporter MntE plays a crucial role in E. faecalis metal homeostasis and virulence.

Sub-Micron Surface Structured Stainless Steel As an Anode for Microbial Fuel Cell

Fossil foil depletion and their environmental impact make it inevitable to find alternative energy resources. One of the promising energy sources is to generate electricity through degrading organic compounds, using biofuel cells. Microbial fuel cells (MFCs) are biofuel cells that produce electricity while treating wastewater, allowing for more sustainable wastewater treatment and energy production1. For MFC to be a real-life application, the material of its components should be efficient, cost-effective, and commercially available. MFCs anodes are the interface where the bio-electrochemical reaction takes place through electron transfer from the bacteria to the electrode to produce an electrical current2. Herein we test a 3D nanostructured 316L stainless steel (SS) anode to provide a high specific surface area for the bacteria to adhere to the surface, and in turn, enhances the bacterial catalytic behavior. Furthermore, the SS nanostructured samples were annealed in various gaseous atmospheres to identify the effect of different surface oxidation states on MFC anodes performance. The surface of the bare SS and the nanostructured anodes were imaged using the field emission scanning electron microscopy (FESEM), before and after using them in the MFCs. The as anodized SS had a 3D nanostructured surface of interconnected nanorods that kept its morphology upon annealing. X-ray diffraction (XRD) was performed at a glancing angle (θ <5°), which interpreted that 316 L as received SS had a face-centered cubic structure that has gamma phase iron with the γ(111), γ (200), γ (220), γ (311), and γ (222) facets 3, while the film formed on the as anodized SS had amorphous regions that were transferred to crystalline film upon annealing for one hour in 450 C temperature. X-ray photoelectron spectroscopy (XPS) was used to characterize the composition of the fabricated SS anodes that interpreted that the film formed on SS was iron-chromium oxyhydroxide film4 and upon annealing the ratio of metal oxides especially Fe2O3 and Fe3O4 increased which increased the metal surface conductivity. The surface conductivity of annealed anodes was tested using cyclic voltammetry (CVs) in the ferricyanide solution. The annealed samples had enhanced to electron transfer kinetics on its surface relative to both the as-received and as anodized samples that showed nearly no redox activity. The fabricated SS samples were tested using a dual-chamber MFCs inoculated with sludge, using acetate as a substrate and potassium ferricyanide as the oxidant in the cathode. The power output of the MFCs with different anodes was observed using a data acquisition system for 20 days. CVs were done on the anodes on the 10th day. The results emphasized that the nanostructured SS samples highly increased cell voltage (≈ 80 times). This enhancement in the MFCs power performance is explained by the enhanced biofilm growth offered by the high specific area for the nanostructured SS. The FESEM images taken after the end of the experiment showed an obvious biomass growth on the surface of the as anodized SS relative to the biofilm on the as-received one. In addition, the annealed samples showed an enhanced activity after annealing. Annealing, especially in O2, increased the surface content of the more biocompatible Fe2O3 component, as interpreted by the XPS, which in turn increased the voltage production (≈ 120 times) relative to the as-received sample. The enhancement of the power generation was further supported using the CVs, with the anodized anode annealed in O2 showing an enhancement anodic current in comparison to smooth SS samples.

Integration of substrate in biofloc based system: Effects on growth performance, water quality and immune responses in black tiger shrimp, Penaeus monodon culture

To evaluate effect of substrate integration in biofloc based system, a 52-day growth experiment was conducted using black tiger shrimp, Penaeus monodon juveniles (3.32 ± 0.07 g). The factorial design consisted of floc, F (with or without) as first factor and substrate (bamboo mat, B; nylon mesh, N; and without substrate) as second factor. This resulted six treatments; F + B, F + N, F, B, N and a control without biofloc and substrate. Shrimps were stocked at 110 nos. m–3 in Fibre Reinforced Plastic (FRP) tanks and, rice flour was used as carbon source in biofloc based treatments. Incorporation of nylon mesh and bamboo mat in biofloc system trapped 31.3%–38.6% and 8.5%–13.5% total suspended solids respectively and reduced bottom solid deposition. Among the substrate based groups, significantly better development of biofilm with higher microbial population noticed in F + B compared with nylon mesh. Similarly, significantly higher final growth (p < 0.01) was recorded in F + B system followed by F + N while no significant difference in body weight recorded among floc, F or substrate based groups (B, N). Biofloc and substrate integration (F + B and F + N) resulted significantly (p < 0.01) lower feed conversion ratio compared to control and floc. Incoporation of bamboo substrate in biofloc, (F + B) improved shrimp immune responses through higher hemocyte counts and prophenoloxidase activity compared to other treatments. The study revealed that integration of substrate in the biofloc system improved growth performance, FCR and immune parameters in shrimp by trapping the suspended biofloc particles, better water quality parameters, enhanced biofilm growth and provision of quality natural food.

Grid columnar flat panel photobioreactor with immobilized photosynthetic bacteria for continuous photofermentative hydrogen production

A biophotoreactor with a transparent glass flat panel with polymethyl methacrylate (PMMA) grid columnar for enhanced biofilm growth with Rhodopseudomonas palustris GCA009 was developed and tested at 590 nm incident light. Continuous photofermentative hydrogen production from glucose was tested using this novel reactor. At light intensity of 210 W/m2, feed substrate concentration of 56.0 mmol/L, and crossflow velocity of 1.68 × 10−6 m/s, a maximum hydrogen production rate of 32.6 mmol/L-d (3.56 mmol/m2-h), hydrogen yield of 1.15 mol H2/mol glucose and light conversion efficiency of 5.34% can be achieved. Since the revised grid columnar effectively enlarged the surface area of reactor and enhanced cell attachment, the present reactor design led to higher hydrogen production rates than literature works.

Biotic and abiotic substrates for enhancing Acinetobacter baumannii biofilm formation: New approach using extracellular matrix and slanted coverslip technique.

Acinetobacter baumannii has been well recognized as a problematic human pathogen and several reports has shown the incidence of multidrug and pandrug-resistant A. baumannii strains in infirmary infections. A. baumannii grows only on an air-liquid interface and does not form a contiguous biofilm. Extracellular matrices (ECM) and slanted glass coverslips are (SGC) used as biofilm substrates and biofilms have been investigated by SEM, confocal and crystal violet staining. ECM has shown enhanced biofilm formation under dynamic conditions rather than static conditions. SGC biofilm yield assay has shown higher levels of continuous layers and packed thicker biofilm formation with glass coverslip inserts, up to 1.7 to 3 times higher biofilm formation, than when compared with no glass coverslip inserts. A media immersed ECM study revealed that biofilm grown on extracellular matrixes formed thread-like pili structures, and that these structures had contact with the ECM and also showed excellent cell-to-cell interaction. In summary, A. baumannii showed higher biofilm formation capacities with ECM, while the prominent results were directly related with the biofilm formation capacity of A. baumannii. For the initial step of biofilm formation, adherence is an important factor and, consequently, strains with a comparatively high capability to adhere to extracellular matrices and slanted glass coverslips provide a new method of enhanced biofilm growth for in vitro assays. ECM can be used as a substrate for immersed biofilm formation studies and the SGC method for air-liquid interface exposed biofilm formation studies, and these substrates can provide better biofilm growth and easy handling for in vitro adherence and biofilm assays.

Extracellular Electron Transfer Powers Enterococcus faecalis Biofilm Metabolism.

ABSTRACTEnterococci are important human commensals and significant opportunistic pathogens. Biofilm-related enterococcal infections, such as endocarditis, urinary tract infections, wound and surgical site infections, and medical device-associated infections, often become chronic upon the formation of biofilm. The biofilm matrix establishes properties that distinguish this state from free-living bacterial cells and increase tolerance to antimicrobial interventions. The metabolic versatility of the enterococci is reflected in the diversity and complexity of environments and communities in which they thrive. Understanding metabolic factors governing colonization and persistence in different host niches can reveal factors influencing the transition to biofilm pathogenicity. Here, we report a form of iron-dependent metabolism for Enterococcus faecalis where, in the absence of heme, extracellular electron transfer (EET) and increased ATP production augment biofilm growth. We observe alterations in biofilm matrix depth and composition during iron-augmented biofilm growth. We show that the ldh gene encoding l-lactate dehydrogenase is required for iron-augmented energy production and biofilm formation and promotes EET.

Altered biofilm formation at plasma bonded surfaces in microchannels studied by attenuated total reflection infrared spectroscopy

This paper is dedicated to Professor P.R. Norton on the occasion of his 75th birthday, in honor of his profound contributions to Surface Science. In this work, we investigate how plasma bonding of a germanium ATR crystal to a microfluidic device can affect biofilm growth and development. Using attenuated total reflection Fourier transform infrared spectroscopy, individual measurements were made at the attachment surface of growing Pseudomonas fluorescens biofilms in adjacent flow channels during parallel experiments. Biofilm growth in channels with ATR surfaces exposed to air plasma exhibited a faster accumulation of a biomolecular conditioning layer compared to unexposed channels. As well, in-line microscopy revealed enhanced bulk biofilm growth in plasma-treated channels. Since the surface chemistry the Ge ATR was only partially recovered to its original state during the three day experiments, it is believed that the enhanced biofilm growth was ultimately due effects of plasma exposure. It is proposed that observations are transferable to microfluidic devices with sealing layers from other hard surfaces such as glass, silicon and plastic due to their ability to retain surface functionalization after plasma exposure. Plasma treatment could, therefore, offer a route to faster start up times for bioreactors, but could also result in unexpected artifacts in other studies.

Biofouling in capillary and spiral wound membranes facilitated by marine algal bloom

Algal-derived organic matter (AOM), particularly transparent exopolymer particles, has been suspected to facilitate biofilm development in membrane systems (e.g., seawater reverse osmosis). This study demonstrates the possible role of AOM on biofouling in membrane systems affected by marine algal blooms. The tendency of AOM from bloom-forming marine algae to adhere to membranes and its ability to enhance biofilm growth were measured using atomic force microscopy, flow cytometry, liquid chromatography and accelerated membrane biofouling experiments. Adhesion force measurements indicate that AOM tends to adhere to clean membranes and even more strongly to AOM-fouled membranes. Batch growth tests illustrate that the capacity of seawater to support bacterial growth can significantly increase with AOM concentration. Biofouling experiments with spiral wound and capillary membranes illustrate that when nutrients availability are not limited in the feed water, a high concentration of AOM – whether in suspension or attached to the membrane – can substantially accelerates biofouling. A significantly lower biofouling rate was observed on membranes exposed to feed water spiked only with AOM or easily biodegradable nutrients. The abovementioned findings indicate that AOM facilitates the onset of membrane biofouling primarily as a conditioning platform and to some extent as a nutrient source for biofilm-forming bacteria.

Effect of oyster shell medium and organic substrate on the performance of a particulate pyrite autotrophic denitrification (PPAD) process

The use of pyrite as an electron donor for biological denitrification has the potential to reduce alkalinity consumption and sulfate by-product production compared with sulfur oxidizing denitrification. This research investigated the effects of oyster shell and organic substrate addition on the performance of a particulate pyrite autotrophic denitrification (PPAD) process. Side-by-side bench-scale studies were carried out in upflow packed bed bioreactors with pyrite and sand, with and without oyster shells as an alkalinity source. Organic carbon addition (10% by volume wastewater) was found to improve PPAD denitrification performance, possibly by promoting mixotrophic metabolism. After organic carbon addition and operation at a six-hour empty bed contact time, total inorganic nitrogen (TIN) removal reached 90% in the column with oyster shells compared with 70% without. SEM images and biofilm protein measurements indicated that oyster shells enhanced biofilm growth. The results indicate that PPAD is a promising technology for treatment of nitrified wastewater.

Biofilm growth and nitrogen uptake responses to increases in nitrate and ammonium availability

Nitrate (NO3 −) and ammonium (NH4 +) are the two major dissolved inorganic nitrogen (DIN) species available in streams. Human activities increase stream DIN concentrations and modify the NO3 −:NH4 + ratio. However, few studies have examined biofilm responses to enrichment of both DIN species. We examined biofilm responses to variation in ambient concentrations and enrichments in either NO3 − or NH4 +. We incubated nutrient diffusing substrata (NDS) bioassays with three treatments (DIN-free, +NO3 − and +NH4 +) in five streams. Biomass-specific uptake rates (U spec ) of NO3 − and NH4 + were then measured using in situ additions of 15N-labeled NO3 − and NH4 +. Biomass (estimated from changes in carbon content) and algal accrual rates, as well as U spec -NO3 − of biofilms in DIN-free treatments varied among the streams in which the NDS had been incubated. Higher ambient DIN concentrations were only correlated with enhanced biofilm growth rates. U spec -NO3 − was one order of magnitude greater and more variable than U spec -NH4 +, however similar relative preference index (RPI) suggested that biofilms did not show a clear preference for either DIN species. Biofilm growth and DIN uptake in DIN-amended NDS (i.e., +NO3 − and +NH4 +) were consistently lower than in DIN-free NDS (i.e., control). Lower values in controls with respect to amended NDS were consistently more pronounced for algal accrual rates and U spec -NO3 − and for the +NH4 + than for the +NO3 − treatments. In particular, enrichment with NH4 + reduced biofilm U spec -NO3 − uptake, which has important implications for N cycling in high NH4 + streams.

Exogenous tyrosol inhibits planktonic cells and biofilms of Candida species and enhances their susceptibility to antifungals.

Tyrosol is a quorum-sensing molecule of Candida albicans able to induce hyphal development in the early and intermediate stages of biofilm growth. In the present study, we evaluated the effect of high concentrations of exogenous tyrosol on planktonic cells and biofilms of C. albicans (n = 10) and C. tropicalis (n = 10), and investigated whether tyrosol could be synergic to antifungals that target cellular ergosterol. Antifungal susceptibility and drug interaction against planktonic cells were investigated by the broth microdilution method. Tyrosol was able to inhibit planktonic cells, with MIC values ranging from 2.5 to 5.0 mM for both species. Synergism was observed between tyrosol/amphotericin B (11/20 strains), tyrosol/itraconazole (18/20 strains) and tyrosol/fluconazole (18/20 strains). Exogenous tyrosol alone or combined with antifungals at both 10 × MIC and 50 × MIC were able to reduce biofilm of both Candida species. Mature biofilms were susceptible to tyrosol alone at 50 × MIC or combined with amphotericin at both 10 × MIC and 50 × MIC. On the other hand, tyrosol plus azoles at both 10 × MIC and 50 × MIC enhanced biofilm growth.

Differential effect of autoinducer 2 of Fusobacterium nucleatum on oral streptococci

Autoinducer 2 (AI-2) is a quorum sensing molecule and plays an important role in dental biofilm formation, mediating interspecies communication and virulence expression of oral bacteria. Fusobacterium nucleatum connects early colonizing commensals and late colonizing periodontopathogens. F. nucleatum AI-2 and quorum sensing inhibitors (QSIs) can manipulate dental biofilm formation. In this study, we evaluated the effect of F. nucleatum AI-2 and QSIs on biofilm formation of Streptococcus gordonii and Streptococcus oralis, which are initial colonizers in dental biofilm. F. nucleatum AI-2 significantly enhanced biofilm growth of S. gordonii and attachment of F. nucleatum to preformed S. gordonii biofilms. By contrast, F. nucleatum AI-2 reduced biofilm growth of S. oralis and attachment of F. nucleatum to preformed S. oralis biofilms. The QSIs, (5Z)-4-bromo-5-(bromomethylene)-2(5H)-furanone and d-ribose, reversed the stimulatory and inhibitory effects of AI-2 on S. gordonii and S. oralis, respectively. In addition, co-culture using a two-compartment system showed that secreted molecules of F. nucleatum had the same effect on biofilm growth of the streptococci as AI-2. Our results demonstrate that early colonizing bacteria can influence the accretion of F. nucleatum, a secondary colonizer, which ultimately influences the binding of periodontopathogens.

The influence of antiscalants on biofouling of RO membranes in seawater desalination

Antiscalants are surface active polyelectrolyte compounds commonly used in reverse osmosis (RO) desalination processes to avoid membrane scaling. In spite of the significant roles of antiscalants in preventing membrane scaling, they are prone to enhance biofilm growth on RO membranes by either altering membrane surface properties or by serving as nutritional source for microorganisms. In this study, the contribution of antiscalants to membrane biofouling in seawater desalination was investigated. The effects of two commonly used antiscalants, polyphosphonate- and polyacrylate-based, were tested. The effects of RO membrane (DOW-Filmtec SW30 HRLE-400) exposure to antiscalants on its physico-chemical properties were studied, including the consequent effects on initial deposition and growth of the sessile microorganisms on the RO membrane surface. The effects of antiscalants on membrane physico-chemical properties were investigated by filtration of seawater supplemented with the antiscalants through flat-sheet RO membrane and changes in surface zeta potential and hydrophobicity were delineated. Adsorption of antiscalants to polyamide surfaces simulating RO membrane's polyamide layer and their effects on the consequent bacterial adhesion was tested using a quartz crystal microbalance with dissipation monitoring technology (QCM-D) and direct fluorescent microscopy. A significant increase in biofilm formation rate on RO membranes surface was observed in the presence of both types of antiscalants. Polyacrylate-based antiscalant was shown to enhance initial cell attachment as observed with the QCM-D and a parallel plate flow cell, due to rendering the polyamide surface more hydrophobic. Polyphosphonate-based antiscalants also increased biofilm formation rate, most likely by serving as an additional source of phosphorous to the seawater microbial population. A thicker biofilm layer was formed on the RO membrane when the polyacrylate-based antiscalant was used. Following these results, a wise selection of antiscalants for scaling control should take into account their contribution to membrane biofouling propensity.