Now showing 1 - 10 of 51
  • Publication
    Comparison of planktonic and biofilm cultures of Pseudomonas fluorescens DSM 8341 cells grown on fluoroacetate
    (American Society for Microbiology, 2009-05) ; ;
    Comparisons between the physiological properties of Pseudomonas fluorescens biofilm cells grown in a tubular biofilm reactor and planktonic cells grown in a chemostat were performed. Fluoroacetate was the sole carbon source for all experiments. The performance of cells was assessed using cell cycle kinetics and by determining specific fluoroacetate utilization rates. Cell cycle kinetics were studied by flow cytometry in conjunction with the fluorescent stain propidium iodide. Determination of the DNA content of planktonic and biofilm cultures showed little difference between the two modes of growth. Cultures with comparable specific glycolate utilization rates had similar percentages of cells in the B phase of the cell cycle, indicating similar growth rates. Specific fluoroacetate utilization rates showed the performance of planktonic cells to be superior to that of biofilm cells, with more fluoroacetate utilized per cell at similar specific fluoroacetate loading rates. A consequence of this decreased biofilm performance was the accumulation of glycolate in the effluent of biofilm cultures. This accumulation of glycolate was not observed in the effluent of planktonic cultures. Spatial stratification of oxygen within the biofilm was identified as a possible explanation for the overflow metabolism of glycolate and the decreased performance of the biofilm cells.
      554Scopus© Citations 33
  • Publication
    Nanofiltration-induced cell death: An integral perspective of early stage biofouling under permeate flux conditions
    The performance of pressure-driven membrane filtration processes for water treatment is hampered by biofouling. A relevant, but often overlooked aspect of this phenomenon concerns the localized microenvironment at the membrane interface. A key question is the level of stress on adhering cells and how this impacts on the developing biofilm. In this study, Pseudomonas fluorescens biofilms were monitored after 1, 2 and 7-day cross-flow nanofiltration experiments using confocal microscopy with live/dead staining which enabled analysis of both biofilm structure and the spatial localization of dead versus live cells. A significant increased level of biomass at low- compared to high-flux conditions (2-day experiments) suggested hindrance of bacterial proliferation at higher fluxes. An increase in live cell fractions was generally observed between 24- and 48-h at low flux conditions (3 bar), while the fraction of dead/injured cells remained constant during that same period. At higher flux conditions (15 bar), the volume of live cell fractions remained constant over 24- and 48-h experiments. The implications of these findings point to the need to reevaluate classical contact-killing strategy for controlling membrane fouling; initial membrane fouling events are characterized by an initially-induced cell death stage followed by an adaptation period through which surviving cells are able to acclimatize in their respective environments. This study emphasizes the need to better understand the role of operating parameters and its resulting cell death during early stage fouling. It is in this context that fouling management strategies can be further developed.
      42Scopus© Citations 6
  • Publication
    Biofilm recruitment under nanofiltration conditions: the influence of resident biofilm structural parameters on planktonic cell invasion
    (Wiley, 2017-12-01) ;
    It is now generally accepted that biofouling is inevitable in pressure-driven membrane processes for water purification. A large number of published articles describe the development of novel membranes in an effort to address biofouling in such systems. It is reasonable to assume that such membranes, even those with antimicrobial properties, when applied in industrial-scale systems will experience some degree of biofouling. In such a scenario, an understanding of the fate of planktonic cells, such as those entering with the feed water, has important implications with respect to contact killing particularly for membranes with antimicrobial properties. This study thus sought to investigate the fate of planktonic cells in a model nanofiltration biofouling system. Here, the interaction between auto-fluorescent Pseudomonas putida planktonic cells and 7-day-old Pseudomonas fluorescens resident biofilms was studied under permeate flux conditions in a nanofiltration cross flow system. We demonstrate that biofilm cell recruitment during nanofiltration is affected by distinctive biofilm structural parameters such as biofilm depth.
      261Scopus© Citations 1
  • Publication
    Simultaneous removal of malachite green and hexavalent chromium by Cunninghamella elegans biofilm in a semi-continuous system
    The present study was conducted to evaluate the potential of the fungus Cunninghamella elegans for simultaneous decolourisation of a triphenylmethane dye malachite green (MG) and hexavalent chromium [Cr(VI)] in the same media. This fungus can degrade MG through its reduction into leucomalachite green and then demethylation followed by oxidative cleavage. Along with MG degradation, C. elegans biofilm could effectively and repeatedly remove Cr(VI) from the liquid cultures even in the presence of high concentrations (40 g L−1) of NaCl and various other metal ions. C. elegans biofilm was also found to adsorb different dyes (reactive black-5, acid orange 7, direct red 81 and brilliant blue G) concurrently with Cr(VI). Based on its potential for simultaneous removal of dyes and Cr(VI) as well as reusability, C. elegans biofilm is envisaged as an efficient bioresource to devise strategies for treatment of wastewaters loaded with multiple pollutants.
      50Scopus© Citations 37
  • Publication
    Tailoring Nanoparticle-Biofilm Interactions to Increase the Efficacy of Antimicrobial Agents Against Staphylococcus aureus
    Background: Considering the timeline required for the development of novel antimicrobial drugs, increased attention should be given to repurposing old drugs and improving anti-microbial efficacy, particularly for chronic infections associated with biofilms. Methicillin-susceptible Staphylococcus aureus (MSSA) and methicillin-resistant S. aureus (MRSA) are common causes of biofilm-associated infections but produce different biofilm matrices.MSSA biofilm cells are typically embedded in an extracellular polysaccharide matrix, whereas MRSA biofilms comprise predominantly of surface proteins and extracellular DNA (eDNA). Nanoparticles (NPs) have the potential to enhance the delivery of antimicro-bial agents into biofilms. However, the mechanisms which influence the interactions between NPs and the biofilm matrix are not yet fully understood. Methods:To investigate the influence of NPs surface chemistry on vancomycin (VAN) encapsulation and NP entrapment in MRSA and MSSA biofilms, mesoporous silica nano-particles (MSNs) with different surface functionalization (bare-B, amine-D, carboxyl-C,aromatic-A) were synthesised using an adapted Stöber method. The antibacterial efficacy of VAN-loaded MSNs was assessed against MRSA and MSSA biofilms. Results: The two negatively charged MSNs (MSN-B and MSN-C) showed a higher VAN loading in comparison to the positively charged MSNs (MSN-D and MSN-A). Cellular binding with MSN suspensions (0.25 mg mL−1) correlated with the reduced viability of both MSSA andMRSA biofilm cells. This allowed the administration of low MSNs concentrations while maintaining a high local concentration of the antibiotic surrounding the bacterial cells. Conclusion: Our data suggest that by tailoring the surface functionalization of MSNs,enhanced bacterial cell targeting can be achieved, leading to a novel treatment strategy for biofilm infections.
      204Scopus© Citations 35
  • Publication
    Simulation studies of process scale membrane aerated biofilm reactor configurations
    In the membrane aerated biofilm reactor oxygen diffuses through the membrane into the biofilm where oxidation of pollutants, supplied from the biofilm side of the membrane takes place. Despite numerous studies at the laboratory scale showing the potential of the technology, efforts to scale-up the technology to process scale have been hampered by problems such as excessive biofilm growth and consequent flow distribution problems. This paper presents results of simulation studies which utilise Computational Fluid Dynamics (CFD) to examine performance of several technical scale MABR design configurations. The simulations suggest that plate-and-frame membrane configuration with a suitable liquid inlet distributor will deliver superior performance compared to hollow fibre configuration with respect to liquid flow distribution.
  • Publication
    Disinfection of a polyamide nanofiltration membrane using ethanol
    It is imperative that nanofiltration membranes are disinfected before they are used for laboratory-scale bacterial adhesion or biofouling experiments, yet currently no suitable disinfection protocol exists. This study aimed to determine if an ethanol treatment at a minimum inhibitory concentration (MIC) could be used to effectively disinfect nanofiltration membranes without altering membrane properties which could affect research. Two strains of bacteria, Pseudomonas fluorescens and Staphylococcus sp., were exposed to a range of ethanol concentrations to determine the MIC required for a 4log10 reduction in bacteria. In parallel, ethanol's effects on the filtration, surface and mechanical properties of a Dow Filmtec NF90 membrane were analysed. A 1.5 hour treatment with 40% ethanol was shown to effectively disinfect the membrane without significantly affecting any of the membranes properties tested. This treatment protocol can now be safely used to disinfect the studied membrane prior to bacterial adhesion or biofouling experiments. This study also acts as a guideline for researchers using other membranes to determine a suitable disinfection protocol for their needs.
      1000Scopus© Citations 29
  • Publication
    Production of Whey-Derived DPP-IV Inhibitory Peptides Using an Enzymatic Membrane Reactor
    Continuous processing in the production of peptides is an area of increased interest. In this study, an enzymatic membrane reactor (EMR) was developed whereby whey protein isolate was used as a substrate to prepare DPP-IV inhibitory and radical scavenging peptides via enzymatic hydrolysis. Two separate enzymes were tested: Corolase 2TS and Protamex in conventional batch processes and the EMR. Neither enzyme was considered effective at producing peptides with radical scavenging activity when measured using a DPPH assay. However, both enzymes were capable of producing DPP-IV inhibitory peptides. Corolase and Protamex both produced similar DPP-IV inhibition levels upon completion of batch experiments. In the EMR process, permeate in the Protamex run showed 33.7% lower IC50 value compared to the continuous Corolase run. Protamex was a better enzyme at producing the DPP-IV inhibitory effect. The continuous (EMR) production method showed an increased productivity over batch for both enzymes.
      619Scopus© Citations 17
  • Publication
    Tracer measurements reveal experimental evidence of biofilm consolidation
    (Wiley, 2007-11-01)
    The ability to simultaneously measure both biofilm thickness and the mass transfer coefficient of an inert tracer through it provides a powerful method to study biofilm development. In this communication previously published data has been collated to interpret global trends in biofilm structure during the transition towards steady-state. It appears that sudden changes in biofilm structure (directly related to the rate of change of biofilm mass transfer resistance) may occur following transitions in rate of biomass production. These observations are consistent with the concept of consolidation, recently introduced into spatially structured biofilm mathematical models to account for structural realignment of the biofilm under dynamic conditions.
      408Scopus© Citations 16
  • Publication
    The importance of laboratory water quality for studying initial bacterial adhesion during NF filtration processes
    Biofouling of nanofiltration (NF) and reverse osmosis (RO) membranes for water treatment has been the subject of increased research effort in recent years. A prerequisite for undertaking fundamental experimental investigation on NF and RO processes is a procedure called compaction. This involves an initial phase of clean water permeation at high pressures until a stable permeate flux is reached. However water quality used during the compaction process may vary from one laboratory to another. The aim of this study was to investigate the impact of laboratory water quality during compaction of NF membranes. A second objective was to investigate if the water quality used during compaction influences initial bacterial adhesion. Experiments were undertaken with NF270 membranes at 15 bar for permeate volumes of 0.5L, 2L, and 5L using MilliQ, deionized or tap water. Membrane autopsies were performed at each permeation point for membrane surface characterisation by contact angle measurements, profilometry, and scanning electron microscopy. The biological content of compacted membranes was assessed by direct epi-fluorescence observation following nucleic acid staining. The compacted membranes were also employed as substrata for monitoring the initial adhesion of Ps. fluorescens under dynamic flow conditions for 30 minutes at 5 minutes intervals. Compared to MilliQ water, membrane compaction using deionized and tap water led to decreases in permeate flux, increase in surface hydrophobicity and led to significant buildup of a homogenous fouling layer composed of both living and dead organisms (>10⁶−2). Subsequent measurements of bacterial adhesion resulted in cell loadings of 0.2×10⁵, 1.0×10⁵cells×cm−2 and 2.6×10⁵−2 for deionized, tap water and MilliQ water, respectively. These differences in initial cell adhesion rates demonstrate that choice of laboratory water can significantly impact the results of bacterial adhesion on NF membranes. Standardized protocols are therefore needed for the fundamental studies of bacterial adhesion and biofouling formation on NF and RO membrane. This can be implemented by first employing pure water during all membrane compaction proceduresand for the modelled feed solutions used in the experiment.
      1048Scopus© Citations 26