Biofilm Age Research Articles

Small colony variants have a major role in stability and persistence of Staphylococcus aureus biofilms.

The present study was conducted to investigate the significance of small colony variants (SCVs) in biofilm life cycle of methicillin-resistant Staphylococcus aureus (MRSA) and methicillin-susceptible S. aureus (MSSA). All of these MRSA and MSSA isolates were recovered from different food commodities. Molecular typing showed that 21 MRSA isolates carry SCCmecA type IV and belong to agr type II. Out of 15 MSSA isolates, 7 were found to carry agr type II, 5 agr type I and 2 agr type III. All of the MRSA isolates studied adopted biofilm mode of growth after exposure to sublethal doses of oxacillin. MSSA isolates, on the other hand, were biofilm producers by nature, that is, without exposure to any stress. The biomass of the biofilm reaches its maximum thickness after 48 h of incubation at 35 °C. It was noticed that biofilm population consists of wild type and SCVs. Moreover, the number of SCVs increases with the age of biofilm. The SCVs of MRSA were unable to readopt biofilm mode of growth independently, irrespective of the presence or absence of oxacillin. The SCVs of MSSA, on the other hand, quickly revert to normal life just after a single subculture and show biofilm formation without any stress. Molecular studies showed a parallel reduction in the expression of the genes icaA, sigβ and sarA, and also in the extracellular matrix production in SCVs of MRSA. This might be due to oxacillin as it seems to be a stress factor responsible for induction of biofilm formation in MRSA isolates. Contrary to the wild type, SCVs are metabolically inactive and do not respond to oxacillin, which is only active against the growing cells. Therefore, stress-responsive genes, that is, sigβ and sarA, are not induced. Conversely, MSSA isolates are natural biofilm producers without induction through any known factors.

Polyphosphate-mediated modulation of Campylobacter jejuni biofilm growth and stability

Biofilms increase C. jejuni’s resilience to detergents, antibiotics, and environmental stressors. In these investigations, we studied the modulation of biofilm in response to phosphate related stressors. We found that the deletion of ppk1, phoX, and ppk2 (polyphosphate associated [poly P] genes) in C. jejuni modulated different stages of biofilm formation such as attached microcolonies, air-liquid biofilms, and biofilm shedding. Additionally, inorganic phosphate also modulated attached microcolonies, air-liquid biofilms, and biofilm shedding both independently of and additively in the poly P associated mutants. Furthermore, we observed that these different biofilm stages were affected by biofilm age: for example, the adherent microcolonies were maximum on day 2, while biofilm growth at the air-liquid interface and shedding was highest on day 3. Also, we observed altered calcofluor white reactive polysaccharides in poly P-associated mutants, as well as increased secretion of autoinducer-2 (AI-2) quorum sensing molecules in the ∆ppk2 mutant. Further, the polysaccharide and flagellar biosynthesis genes, that are associated with biofilm formation, were altered in these poly P-associated mutants. We conclude that the phosphate limiting condition modulates C. jejuni biofilm formation.

Importance of biofilm age and growth medium on the viability of probiotic capsules containing Lactobacillus rhamnosus GG biofilm

Health benefits conferred by probiotic organism Lactobacillus rhamnosus GG taken as food supplements to its human hosts have been well established clinically. Probiotic capsules containing biofilm form of L. rhamnosus GG was shown very recently to exhibit greater freeze drying and thermal tolerance than their planktonic cell counterparts. Herein we examine the impacts of biofilm age (1, 3, and 5 days) and growth medium (Lactobacilli broth de Man, Rogosa and Sharpe (MRS) or Lactobacilli broth according to the Association of Official Analytical Chemists (AOAC)) on the biofilm capsules' tolerance towards stresses typically encountered in food product lifecycle, i.e. freeze drying, two-week storage at 4 °C, heating at 100 °C, and simulated gastrointestinal juice exposure. While freeze drying and thermal tolerance are minimally affected, storage and gastrointestinal viabilities are highly dependent on biofilm age and growth medium. Capsules prepared in AOAC exhibit higher cell viabilities than those prepared in MRS attributed to higher extracellular polymeric substance (EPS) in the former. Mature biofilm capsules (>1 day) survive storage better, however, their gastrointestinal juice viability is compromised, particularly for MRS capsules. The best overall viability is obtained from 5-day-old biofilm capsules in AOAC.

Evaluation of Streptococcus mutans adhesion to fluoride varnishes and subsequent change in biofilm accumulation and acidogenicity

ObjectivesThe aim of this study was to evaluate Streptococcus mutans adhesion to fluoride varnishes and subsequent change in biofilm accumulation and acidogenicity. MethodsAfter producing fluoride varnish-coated hydroxyapatite discs using Fluor Protector (FP), Bifluorid 12 (BIF), Cavity Shield (CASH), or Flor-Opal Varnish White (FO), S. mutans biofilms were formed on the discs. To assess S. mutans adhesion to the discs, 4-h-old biofilms were analysed. To investigate the change in biofilm accumulation during subsequent biofilm formation, the biomass, colony forming units (CFU), and water-insoluble extracellular polysaccharides (EP) of 46-, 70-, and 94-h-old biofilms were analysed. To investigate the change in acidogenicity, pH values of the culture medium were determined during the experimental period. The amount of fluoride in the culture medium was also determined during the experimental period. ResultsBIF, CASH, and FO affected S. mutans adhesion (67–98% reduction) and subsequent biofilm accumulation in 46-, 70-, and 94-h-old biofilms. However, the reducing effect of the fluoride varnishes on the biomass, CFU count, water-insoluble EP amount, and acid production rate of the biofilms decreased as the biofilm age increased. These results may be related to the fluoride-release pattern of the fluoride varnishes. Of the fluoride varnishes tested, FO showed the highest reducing effect against the bacterial adhesion and subsequent biofilm accumulation. ConclusionsOur findings suggest that if the results of these experiments are extrapolable to the in vivo situation, then reduced clinical benefit of using fluoride varnishes may occur with time. Clinical significanceFluoride varnish application can affect cariogenic biofilm formation but the anti-biofilm activity may be reduced with time.

Bacterial dynamics in a microphytobenthic biofilm: A tidal mesocosm approach

In intertidal mudflats, during low tide exposure, microphytobenthos (MPB) migrate vertically through the surface sediment and form, with the heterotrophic bacteria, a transient biofilm. Inside this biofilm, multiple interactions exist between MPB and bacteria. These micro-organisms secrete a wide range of extracellular polymeric substances (EPS), which are major components of the biofilm matrix. In this study, we used a tidal mesocosm experiment in order to decipher the interactions of the MPB–EPS–bacteria complex within the biofilm. We tried to determine if the EPS could control bacterial activities and/or production and/or richness according to the age of the biofilm and to the immersion/emersion period. The dynamics of biomasses of MPB and prokaryotes, the bacterial production, the hydrolysis of predominating organic constituents in the dissolved organic carbon (DOC) pool (i.e., carbohydrates and polypeptides), and the bacterial structure were studied in relation to the different EPS fractions (carbohydrates and proteins: colloidal and bound) dynamics during 8days. Our experiment had emphasized the influence of the environmental conditions (light, immersion/emersion) on the interactions within the biofilm and also on the effects on biofilm aging. Bacterial production was always inhibited by the bound EPS-carbohydrate, especially during low tide. Our results suggest that the concentration and composition of EPS had a major role in the bacterial/MPB interactions: these interactions can be either positive or negative in order to regulate the productive phases of MPB and bacteria.

Transport of Industrial PVP-Stabilized Silver Nanoparticles in Saturated Quartz Sand Coated with Pseudomonas aeruginosa PAO1 Biofilm of Variable Age

Understanding the environmental fate and transport of engineered nanoparticles (ENPs) is of paramount importance for the formation and validation of regulatory guidelines regarding these new and increasingly prevalent materials. The present study assessed the transport of an industrial formulation of poly(vinylpyrrolidone)-stabilized silver nanoparticle (PVP-nAg) in columns packed with water-saturated quartz sand and the same sand coated with Pseudomonas aeruginosa PAO1 biofilm of variable age (i.e., growth period). Physicochemical characterization studies indicate that the PVP-nAg is stable in suspension and exhibits little change in size or electrophoretic mobility with changing ionic strength (IS) in either NaNO3 or Ca(NO3)2. The collector surface had a relatively homogeneous biofilm coating, as determined by CLSM, and a near uniform distribution of biomass and biofilm thickness following column equilibration. Transport experiments in clean sand revealed changes in the particle deposition behavior only at and above 10 mM IS Ca(NO3)2 and showed no discernible change in PVP-nAg transport behavior in the presence of 1 to 100 mM NaNO3. Transport experiments in P. aeruginosa-coated sand indicated significantly reduced retention of PVP-nAg at low IS compared to clean sand, irrespective of biofilm age. Nanoparticle retention was also generally reduced in the biofilm-coated sand at the higher IS, but to a lesser extent. The decreased retention of PVP-nAg in biofilm-coated sand compared to clean sand is likely due to repulsive electrosteric forces between the PVP coatings and extracellular polymeric substances (EPS) of the biofilm. Additionally, the slope of the rising portion of the PVP-nAg breakthrough curve was noticeably steeper in biofilm conditions than in clean sand. More mature biofilm coating also resulted in earlier breakthrough of PVP-nAg compared to younger biofilm coatings, or to the clean sand, which may be an indication of the effect of repulsive surface forces combined with selective pore size exclusion from the pores of denser, more developed biofilm. These results, when considered with other literature, indicate the importance in considering the flow dynamics, pore network and structure, the effective particle size, and particle permeability with regard to the biofilm matrix when considering the possible influence of biofilms on ENP transport.

Sponge larval settlement cues: the role of microbial biofilms in a warming ocean

Microbial biofilms play important roles in initiating settlement of marine invertebrate larvae. Given the importance of habitat selection by the motile larval phase, understanding settlement choices is critical if we are to successfully predict the population dynamics of sessile adults. Marine microbial biofilms show remarkable variability in community composition, often mediated by environmental conditions and biofilm age. To determine if biofilm communities were influenced by the time allowed to establish (age) and/or seawater temperature, we manipulated experimental surfaces to firstly determine biofilm community composition and secondly test larval settlement responses for the abundant coral reef sponge Rhopaloeides odorabile. Microbial profiling of biofilms revealed different communities according to both age and temperature. Biofilm community composition, as a result of both elevated seawater temperature and biofilm age, contributed to settlement for sponge larvae with markedly higher numbers of larvae settling to biofilms developed over longer periods (10 d) and at temperatures 2–6°C above ambient.

Effect of growth temperature, surface type and incubation time on the resistance of Staphylococcus aureus biofilms to disinfectants

The goal of this study was to investigate the effect of the environmental conditions such as the temperature change, incubation time and surface type on the resistance of Staphylococcus aureus biofilms to disinfectants. The antibiofilm assays were performed against biofilms grown at 20 °C, 30 °C and 37 °C, on the stainless steel and polycarbonate, during 24 and 48 h. The involvement of the biofilm matrix and the bacterial membrane fluidity in the resistance of sessile cells were investigated. Our results show that the efficiency of disinfectants was dependent on the growth temperature, the surface type and the disinfectant product. The increase of growth temperature from 20 °C to 37 °C, with an incubation time of 24 h, increased the resistance of biofilms to cationic antimicrobials. This change of growth temperature did not affect the major content of the biofilm matrix, but it decreased the membrane fluidity of sessile cells through the increase of the anteiso-C19 relative amount. The increase of the biofilm resistance to disinfectants, with the rise of the incubation time, was dependent on both growth temperature and disinfectant product. The increase of the biofilm age also promoted increases in the matrix production and the membrane fluidity of sessile cells. The resistance of S. aureus biofilm seems to depend on the environment of the biofilm formation and involves both extracellular matrix and membrane fluidity of sessile cells. Our study represents the first report describing the impact of environmental conditions on the matrix production, sessile cells membrane fluidity and resistance of S. aureus biofilms to disinfectants.

Synergistic effect of xylitol and ursolic acid combination on oral biofilms.

ObjectivesThis study was designed to evaluate the synergistic antibacterial effect of xylitol and ursolic acid (UA) against oral biofilms in vitro.Materials and MethodsS. mutans UA 159 (wild type), S. mutans KCOM 1207, KCOM 1128 and S. sobrinus ATCC 33478 were used. The susceptibility of S. mutans to UA and xylitol was evaluated using a broth microdilution method. Based on the results, combined susceptibility was evaluated using optimal inhibitory combinations (OIC), optimal bactericidal combinations (OBC), and fractional inhibitory concentrations (FIC). The anti-biofilm activity of xylitol and UA on Streptococcus spp. was evaluated by growing cells in 24-well polystyrene microtiter plates for the biofilm assay. Significant mean differences among experimental groups were determined by Fisher's Least Significant Difference (p < 0.05).ResultsThe synergistic interactions between xylitol and UA were observed against all tested strains, showing the FICs < 1. The combined treatment of xylitol and UA inhibited the biofilm formation significantly and also prevented pH decline to critical value of 5.5 effectively. The biofilm disassembly was substantially influenced by different age of biofilm when exposed to the combined treatment of xylitol and UA. Comparing to the single strain, relatively higher concentration of xylitol and UA was needed for inhibiting and disassembling biofilm formed by a mixed culture of S. mutans 159 and S. sobrinus 33478.ConclusionsThis study demonstrated that xylitol and UA, synergistic inhibitors, can be a potential agent for enhancing the antimicrobial and anti-biofilm efficacy against S. mutans and S. sobrinus in the oral environment.

Antimicrobial Efficacy of Photodynamic Therapy and Sodium Hypochlorite on Monoculture Biofilms of Enterococcus faecalis at Different Stages of Development

As the Enterococcus faecalis biofilm ages, it is likely that bacteria in mature and old biofilms will become more resistant to commonly used antibacterial irrigants. Photodynamic therapy (PDT) has been used to kill resistant bacteria organized in a biofilm. This study aimed to investigate the antimicrobial effectiveness of 1% sodium hypochlorite (NaOCl), 2.5% NaOCl, and PDT on E. faecalis biofilm at different stages of development. In this study 4-, 6-, and 8-week-old E. faecalis biofilms were subjected to one of the following approaches: phosphate-buffered saline solution (PBS), PDT, or 1% and 2.5% NaOCl. Dentin chip suspensions were used for colony forming units (CFU) counting to estimate remaining E. faecalis counts. PDT and 2.5% NaOCl completely eliminated E. faecalis biofilms in three stages of biofilm development, whereas 1% NaOCl resulted in 81.88%, 85.73%, and 78.62% reductions of bacterial counts in 4-, 6-, and 8-week-old biofilms, respectively, which was significantly more than PBS. The bacteria in mature and old biofilms were more resistant to 1% NaOCl than were the bacteria in young biofilms. Overall survival and residual bacteria increase with biofilm aging. PDT and the 2.5% NaOCl solution were equally efficient in completely eliminating E. faecalis biofilms at all three stages.

Kinetic Study of Seawater Reverse Osmosis Membrane Fouling

Reverse osmosis (RO) membrane fouling is not a static state but a dynamic phenomenon. The investigation of fouling kinetics and dynamics of change in the composition of the foulant mass is essential to elucidate the mechanism of fouling and foulant-foulant interactions. The aim of this work was to study at a lab scale the fouling process with an emphasis on the changes in the relative composition of foulant material as a function of operating time. Fouled membrane samples were collected at 8 h, and 1, 2, and 4 weeks on a lab-scale RO unit operated in recirculation mode. Foulant characterization was performed by CLSM, AFM, ATR-FTIR, pyrolysis GC-MS, and ICP-MS techniques. Moreover, measurement of active biomass and analysis of microbial diversity were performed by ATP analysis and DNA extraction, followed by pyro-sequencing, respectively. A progressive increase in the abundance of almost all the foulant species was observed, but their relative proportion changed over the age of the fouling layer. Microbial population in all the membrane samples was dominated by specific groups/species belonging to Proteobacteria and Actinobacteria phyla; however, similar to abiotic foulant, their relative abundance also changed with the biofilm age.

Dynamics of grazing protozoa follow that of microalgae in natural biofilm communities

This study investigates the dynamics of protozoan community in biofilms formed on inert artificial surfaces suspended in various freshwater environments. The results also test the hypothesis that the dynamics of protozoan and microalgal communities in biofilms are interdependent because the latter form one of the major food items of benthic protozoa. Cleaned glass slides were suspended in surface waters at four sampling locations to collect biofilm communities. The glass slides after retrieval were observed under a microscope for diatom and protozoan density and their generic composition. Members of protozoa belonging to phylum Sarcomastigophora dominated the protozoan community followed by phylum Ciliophora in all sampling locations. The variation of protozoan feeding groups showed an initial abundance of autotrophs/holophytes which gave way to heterotrophs, predators, and bacterivores towards the end of the study. The density and generic composition of protozoa varied significantly with the age of biofilm and sampling location. The density variation of protozoa followed that of diatoms in all four sampling locations and this has resulted in a significant positive correlation between diatom and protozoan densities. This suggests the dependency and/or food web connectedness of these two communities in natural biofilms.

Invasion of E. coli biofilms by antibiotic resistance plasmids

In spite of the contribution of plasmids to the spread of antibiotic resistance in human pathogens, little is known about the transferability of various drug resistance plasmids in bacterial biofilms. The goal of this study was to compare the efficiency of transfer of 19 multidrug resistance plasmids into Escherichia coli recipient biofilms and determine the effects of biofilm age, biofilm-donor exposure time, and donor-to-biofilm attachment on this process. An E. coli recipient biofilm was exposed separately to 19 E. coli donors, each with a different plasmid, and transconjugants were determined by plate counting. With few exceptions, plasmids that transferred well in a liquid environment also showed the highest transferability in biofilms. The difference in transfer frequency between the most and least transferable plasmid was almost a million-fold. The ‘invasibility’ of the biofilm by plasmids, or the proportion of biofilm cells that acquired plasmids within a few hours, depended not only on the type of plasmid, but also on the time of biofilm exposure to the donor and on the ability of the plasmid donor to attach to the biofilm, yet not on biofilm age. The efficiency of donor strain attachment to the biofilm was not affected by the presence of plasmids. The most invasive plasmid was pHH2-227, which based on genome sequence analysis is a hybrid between IncU-like and IncW plasmids. The wide range in transferability in an E. coli biofilm among plasmids needs to be taken into account in our fight against the spread of drug resistance.

Biofilm formation vs. PCB adsorption on granular activated carbon in PCB-contaminated aquatic sediment

Purpose: Granular activated carbon (GAC) that is both an efficient PCB adsorbent and a good growth support for microorganisms is considered suitable for in-situ remediation of PCB-contaminated aquatic sediments. Here the potential competition between biofilm formation and PCB (Aroclor 1260) adsorption on GAC in a PCB-contaminated aquatic sediment is investigated. Materials and methods: GACs, both coated and uncoated with biofilm or PCBs, were incubated with sediment. Each was monitored for biofilm development and PCB adsorption by a) cryo-scanning electron microscopy, b) real-time quantitative PCR analysis of the 16S rRNA, c) T-RFLP (Terminal Restriction Fragment Length Polymorphism), and d) chemical analysis, respectively. Results and discussion: Biofilm formation on the GAC by the sediment's bacteria was rapid and occurred in three stages: initial adherence of discrete bacteria; an increase in biomass associated with a shift in bacterial diversity; and exopolymeric matrix production. The density and biodiversity of the multispecies biofilm depended on the biofilm's age. The addition of Aroclor 1260 to the sediment resulted in a decrease of the biofilm biomass, whereas Aroclor 1260 previously adsorbed on the GAC prior to contact with the sediment did not affect the biofilm biomass or its formation dynamics. Similarly, a biofilm previously developed on the GAC did not significantly decrease PCB adsorption, although contact of the GAC with the sediment did hamper adsorption of the higher chlorinated PCB congeners. Conclusions: A mature multispecies bacterial biofilm developed in one month on GAC in contact with aquatic sediment does not hamper PCB adsorption, and PCB adsorption does not affect biofilm formation. Those findings are important for the application of remediation strategies.

Effect of the Source of Biofilm Bacteria, Level of Biofilm Maturation, and Type of Disinfecting Agent on the Susceptibility of Biofilm Bacteria to Antibacterial Agents

IntroductionBiofilm development is a dynamic process that begins with the initial attachment of planktonic bacteria to a surface, eventually leading through different stages to a mature, structurally complex biofilm. The aim of this study was to assess the effect of the source of biofilm bacteria, the level of biofilm maturation, and the type of disinfecting agent on the susceptibility of biofilm bacteria to antibacterial agents. MethodsMultispecies biofilms from plaque bacteria of 6 donors were grown for up to 8 weeks on collagen-coated hydroxyapatite disks. After 1, 2, 3, 4, and 8 weeks of growth the biofilms were exposed to 1% sodium hypochlorite, 0.2/0.4% iodine-potassium iodide, and 2% chlorhexidine for 1 and 3 minutes. The percentage of killed biofilm bacteria was determined by using LIVE/DEAD viability staining and confocal laser scanning microscopy. One-way analysis of variance was used for statistical analysis. ResultsOne- and 2-week-old biofilms were moderately or very sensitive to the tested disinfecting agents, which killed 20%–100% of the biofilm bacteria. After 3 weeks of growth the biofilm bacteria were more resistant to the same agents, and only 10%–30% of the bacteria were killed (P < .001). The same pattern of the effect of biofilm age (maturation) on the resistance of bacteria was observed in all 6 biofilms and with all 3 disinfecting agents. ConclusionThe change of biofilm bacteria from sensitive to resistant against disinfecting agents occurred between 2 and 3 weeks of biofilm maturation. This development took place simultaneously in all biofilms grown from plaque bacteria from 6 different donors and was independent of the type of disinfecting agent used. The results emphasize the importance of knowing the maturation timeline of each biofilm model used to test the effectiveness of endodontic disinfecting agents against biofilm bacteria.

Starvation, Together with the SOS Response, Mediates High Biofilm-Specific Tolerance to the Fluoroquinolone Ofloxacin

High levels of antibiotic tolerance are a hallmark of bacterial biofilms. In contrast to well-characterized inherited antibiotic resistance, molecular mechanisms leading to reversible and transient antibiotic tolerance displayed by biofilm bacteria are still poorly understood. The physiological heterogeneity of biofilms influences the formation of transient specialized subpopulations that may be more tolerant to antibiotics. In this study, we used random transposon mutagenesis to identify biofilm-specific tolerant mutants normally exhibited by subpopulations located in specialized niches of heterogeneous biofilms. Using Escherichia coli as a model organism, we demonstrated, through identification of amino acid auxotroph mutants, that starved biofilms exhibited significantly greater tolerance towards fluoroquinolone ofloxacin than their planktonic counterparts. We demonstrated that the biofilm-associated tolerance to ofloxacin was fully dependent on a functional SOS response upon starvation to both amino acids and carbon source and partially dependent on the stringent response upon leucine starvation. However, the biofilm-specific ofloxacin increased tolerance did not involve any of the SOS-induced toxin–antitoxin systems previously associated with formation of highly tolerant persisters. We further demonstrated that ofloxacin tolerance was induced as a function of biofilm age, which was dependent on the SOS response. Our results therefore show that the SOS stress response induced in heterogeneous and nutrient-deprived biofilm microenvironments is a molecular mechanism leading to biofilm-specific high tolerance to the fluoroquinolone ofloxacin.

Diffusion in biofilms respiring on electrodes

The goal of this study was to measure spatially and temporally resolved effective diffusion coefficients (D(e)) in biofilms respiring on electrodes. Two model electrochemically active biofilms, Geobacter sulfurreducens PCA and Shewanella oneidensis MR-1, were investigated. A novel nuclear magnetic resonance microimaging perfusion probe capable of simultaneous electrochemical and pulsed-field gradient nuclear magnetic resonance (PFG-NMR) techniques was used. PFG-NMR allowed noninvasive, nondestructive, high spatial resolution in situ D(e) measurements in living biofilms respiring on electrodes. The electrodes were polarized so that they would act as the sole terminal electron acceptor for microbial metabolism. We present our results as both two-dimensional D(e) heat maps and surface-averaged relative effective diffusion coefficient (D(rs)) depth profiles. We found that 1) D(rs) decreases with depth in G. sulfurreducens biofilms, following a sigmoid shape; 2) D(rs) at a given location decreases with G. sulfurreducens biofilm age; 3) average D(e) and D(rs) profiles in G. sulfurreducens biofilms are lower than those in S. oneidensis biofilms-the G. sulfurreducens biofilms studied here were on average 10 times denser than the S. oneidensis biofilms; and 4) halting the respiration of a G. sulfurreducens biofilm decreases the D(e) values. Density, reflected by D(e), plays a major role in the extracellular electron transfer strategies of electrochemically active biofilms.

Cleaning of biologically fouled membranes with self-collapsing microbubbles

Increasing global demand for water reclamation has driven the widespread development of membrane processes, where membrane biofouling due to microbial attachment onto membrane surfaces remains the biggest challenge. Given the potential ability of microbubbles (MBs) to generate pressure waves upon collapse, the responses of biofilms of different ages on nylon membrane surfaces towards self-collapsing air MBs was investigated. Changes in the fixed biomass, extracellular polysaccharides and proteins were determined for 3-h, 12-h, 18-h and 24-h old biofilms before and after treatment with MBs. The resistance-in-series model was further applied for analysis of various resistances after treatment of biofilms of different ages with MBs. The results showed substantial flux recovery 1 h after MB treatment for stationary phase biofilms in comparison with initial and exponential growth phase biofilms, which was consistent with the relatively larger percentage reduction in fixed biomass, extracellular polysaccharides and proteins for stationary phase biofilms. However, pore blocking still remained a big challenge even after treatment with MBs, regardless of biofilm age. The experimental data were further supported by confocal laser scanning microscope images. Collapsing MBs appear to be an alternative green chemical-free technology for mitigation of membrane biofouling.

Factors Associated with Alkali Production from Arginine in Dental Biofilms

Alkali production by oral bacteria in the oral cavity has been linked to protection against dental caries. The current study assessed various parameters associated with ammonium produced during arginine catabolism in dental biofilms. Polymicrobial biofilms were formed with saliva as the inoculum. The NH3 level and the pH of the spent medium were used to monitor and quantitate the bacterial reactions. The presence of sucrose, a low buffer capacity, and a low pH (≤ pH 4.5) were found to hamper alkali production from arginine. The rate of alkali production exhibited an optimum around pH 5.5. Biofilms were found to produce NH3 also from polypeptides and proteins in the medium. The biofilm age affected these processes. The experimental model proved valuable for the assessment of the collective bacterial reactions determining the overall pH outcome. This experimental approach could bridge the gap in our knowledge between pH-rise phenomena and caries susceptibility from clinical observations and studies performed on alkali-producing bacteria in well- controlled, though simplified, in vitro models. Analysis of our data supports the hypothesis that the initiation and progression of dental caries may be influenced by the relative rates of acid and base formation, which critically depend on the aforementioned parameters.

Effect of biofilm age on settlement of Mytilus edulis

Biofilm ageing is commonly assumed to improve mussel settlement on artificial substrata, but the structure and taxonomic composition of biofilms remains unclear. In the present study, multi-species biofilms were characterized at different ages (1, 2, and 3 weeks) and their influence on settlement of the blue mussel, Mytilus edulis, was tested in the field. As biofilms can constitute a consistent food resource for larvae, the lipid quality, defined as the proportion of related essential fatty acids, may be a selection criterion for settlement. Overall mussel settlement increased on biofilms older than 1 week, and the enhanced settlement corresponded to the abundance and composition of the biofilm community, rather than to essential fatty acid levels. However, during a pulse of phytoplankton, the positive influence of biofilm was not detected, suggesting that pelagic cues overwhelmed those associated with biofilms. The influence of biofilms on mussel settlement could be more crucial when planktonic resources are limited.