Sang-Ryoung Kim

Biofouling control with bead-entrapped quorum quenching bacteria in membrane bioreactors: physical and biological effects.

Recently, interspecies quorum quenching by bacterial cells encapsulated in a vessel was described and shown to be efficient and economically feasible for biofouling control in membrane bioreactors (MBRs). In this study, free-moving beads entrapped with quorum quenching bacteria were applied to the inhibition of biofouling in a MBR. Cell entrapping beads (CEBs) with a porous microstructure were prepared by entrapping quorum quenching bacteria ( Rhodococcus sp. BH4) into alginate beads. In MBRs provided with CEBs, the time to reach a transmembrane pressure (TMP) of 70 kPa was 10 times longer than without CEBs. The mitigation of biofouling was attributed to both physical (friction) and biological (quorum quenching) effects of CEBs, the latter being much more important. Because of the quorum quenching effect of CEBs, microbial cells in the biofilm generated fewer extracellular polymeric substances and thus formed a loosely bound biofilm, which enabled it to slough off from the membrane surface more easily. Furthermore, collisions between the moving CEBs and membranes gave rise to frictional forces that facilitated detachment of the biofilm from the membrane surface. CEBs bring bacterial quorum quenching closer to being a practical solution to the problem of biofouling in MBRs.

Microbial population dynamics and proteomics in membrane bioreactors with enzymatic quorum quenching

Quorum sensing gives rise to biofilm formation on the membrane surface, which in turn causes a loss of water permeability in membrane bioreactors (MBRs) for wastewater treatment. Enzymatic quorum quenching was reported to successfully inhibit the formation of biofilm in MBRs through the decomposition of signal molecules, N-acyl homoserine lactones (AHLs). The aim of this study was to elucidate the mechanisms of quorum quenching in more detail in terms of microbial population dynamics and proteomics. Microbial communities in MBRs with and without a quorum quenching enzyme (acylase) were analyzed using pyrosequencing and compared with each other. In the quorum quenching MBR, the rate of transmembrane pressure (TMP) rise-up was delayed substantially, and the proportion of quorum sensing bacteria with AHL-like autoinducers (such as Enterobacter, Pseudomonas, and Acinetobacter) also decreased in the entire microbial community of mature biofilm in comparison to that in the control MBR. These factors were attributed to the lower production of extracellular polymeric substances (EPS), which are known to play a key role in the formation of biofilm. Proteomic analysis using the Enterobacter cancerogenus strain ATCC 35316 demonstrates the possible depression of protein expression related to microbial attachments to solid surfaces (outer membrane protein, flagellin) and the agglomeration of microorganisms (ATP synthase beta subunit) with the enzymatic quorum quenching. It has been argued that changes in the microbial population, EPS and proteins via enzymatic quorum quenching could inhibit the formation of biofilm, resulting in less biofouling in the quorum quenching MBR.

Biofouling inhibition in MBR by Rhodococcus sp. BH4 isolated from real MBR plant

It has been reported that an indigenous quorum quenching bacterium, Rhodococcus sp. BH4, which was isolated from a real plant of membrane bioreactor (MBR) has promising potential to control biofouling in MBR. However, little is known about quorum quenching mechanisms by the strain BH4. In this study, various characteristics of strain BH4 were investigated to elucidate its behavior in more detail in the mixed liquor of MBR. The N-acyl homoserine lactone hydrolase (AHL–lactonase) gene of strain BH4 showed a high degree of identity to qsdA in Rhodococcus erythropolis W2. The LC-ESI-MS analysis of the degradation product by strain BH4 confirmed that it inactivated AHL activity by hydrolyzing the lactone bond of AHL. It degraded a wide range of N-acyl homoserine lactones (AHLs), but there was a large difference in the degradation rate of each AHL compared to other reported AHL–lactonase-producing strains belonging to Rhodococcus genus. Its quorum quenching activity was confirmed not only in the Luria-Bertani medium, but also in the synthetic wastewater. Furthermore, the amount of strain BH4 encapsulated in the vessel as well as the material of the vessel substantially affected the quorum quenching activity of strain BH4, which provides useful information, particularly for the biofouling control in a real MBR plant from an engineering point of view.

Enhanced biosynthesis of clavulanic acid in Streptomyces clavuligerus due to oxidative challenge by redox-cycling agents

Streptomyces clavuligerus produces a clinically important β-lactamase inhibitor, clavulanic acid. When several of the selected redox-cycling agents were treated, an increase in clavulanate production was observed. The stimulatory effect was seen when the reaction was fed with menadione, plumbagin and phenazine methosulfate (PMS), whereas feeding with methyl viologen had a negative effect. PMS exerted the strongest effect, enhancing the accumulation of clavulanic acid by 150%. Induction of superoxide dismutase upon the addition of PMS suggested an involvement of superoxide in the enhancing process. The stimulatory effect of PMS was offset by the addition of butylated hydroxyanisole, further supporting the involvement of the active oxygen. The enhanced production of clavulanic acid correlated well with the increased total activity of clavaminic acid synthase, a key enzyme in its biosynthesis, and the transcription of cas2, its coding gene. The results suggested that active oxygen species could enhance the biosynthesis of secondary metabolites through the transcriptional activation of the biosynthetic gene.

Self-Healing Hydrogel Pore-Filled Water Filtration Membranes

Damages to water filtration membranes during installation and operation are known to cause detrimental loss of the product water quality. Membranes that have the ability to self-heal would recover their original rejection levels autonomously, bypassing the need for costly integrity monitoring and membrane replacement practices. Herein, we fabricated hydrogel pore-filled membranes via in situ graft polymerization of 2-acrylamido-2-methyl-1-propanesulfonic acid (AMPS) onto microporous poly(ether sulfone) (PES) substrates and successfully demonstrated their self-healing ability. Covalent attachment of the hydrogel to the substrate was essential for stable membrane performance. The membranes autonomously restore their particle rejection up to 99% from rejection levels as low as 30% after being physically damaged. We attribute the observed self-healing property to swelling of the pore-filling hydrogel into the damage site, strong hydrogen bonding, and molecular interdiffusion. The results of this study show that hydrogel pore-filled membranes are a promising new class of materials for fabricating self-healing membranes.

Evaluation of mechanical membrane cleaning with moving beads in MBR using Box–Behnken response surface methodology

AbstractIncorporation of moving beads into membrane bioreactor (MBR) has been suggested as an effective membrane fouling control because moving beads can mechanically remove bio-cakes on the membrane surface without additional equipment and energy input. As the efficiency of fouling control is dependent on factors associated with moving beads, however, the design of experiment was applied to find optimum condition for the effective mechanical cleaning with moving beads in MBR. Bead diameter (mm), bead number, and aeration rate (m3/h) were selected as independent design parameters. Based on batch test results, the correlation between the detachment efficiency of bio-cakes and three design parameters was established using Box–Behnken methodology. When all three design parameters at their optimal conditions (beadopt) were extended to the continuous lab-scale MBR, membrane filterability increased by three times, compared with that in the control MBR without bead. On the other hand, each of five experimental s...

In Situ Healing of Compromised Membranes via Polyethylenimine-Functionalized Silica Microparticles

Microscale damages to membranes used in large-scale filtration processes for water treatment can result in severe degradation of product water quality. One promising technology to address this issue is in situ healing of compromised membranes via healing agents that are added to the feed side of a membrane system and seal the defect site because of increased hydraulic drag through damage site during filtration. We herein introduce an improved in situ membrane healing method using amine-functionalized silica microparticles that is effective under varying operating conditions, overcoming limitations faced by previous healing agents such as chitosan agglomerates. The silica microparticles are functionalized with branched polyethylenimine (PEI) molecules for efficient interparticle cross-linking with glutaraldehyde. The PEI-decorated silica microparticles (SiO2@PEI MPs) were characterized using scanning electron microscopy, dynamic light scattering, and zeta potential analysis. This study investigates the selective deposition of the SiO2@PEI MPs on the damage area using confocal laser scanning microscopy under variable cross-flow rate (0.5-2.0 L/min) and flushing time (10 to 30 min) conditions. The in situ healing technique recovered the particle rejection of compromised membranes to 99.1% of the original membranes performance without any flux decline. The results of this study show that the use of SiO2@PEI MPs is a promising and practical approach to ensure membrane process integrity.

Molecular basis for enhanced biosynthesis of clavulanic acid by a redox-cycling agent, phenazine methosulfate, in Streptomyces clavuligerus.

Abstract Phenazine methosulfate (PMS), a generator of superoxide, evoked the transcription of cas2 and cefF, ultimately resulting in the enhanced biosyntheses of clavulanic acid (CA) and cephamycin C (CMC) in Streptomyces clavuligerus. The transcriptional activation of cas2 and cefF was accompanied with that of ccaR, a regulatory gene for biosyntheses of CA and CMC. PMS or H2O2 in cell-free extract exerted a positive regulation on in vitro protein phosphorylation. The PMS-mediated activation of protein phosphorylation was significantly offset by butylated hydroxyanisole, a radical scavenger. Staurosporine, a protein kinase inhibitor, was shown to have a negative effect on PMS-promoted CA accumulation. Therefore, it is suggestive that PMS-activated transcription of cas2 and cefF is mediated by protein phosphorylation and the expression of a pathway- specific transcriptional activator as found in other streptomycetes. These experimental results present an example of the functional relationship between oxidative stimuli and secondary metabolite production in streptomycetes.

Decrease of Pseudomonas aeruginosa biofilm formation by food waste materials

The formation of bacterial biofilm on various surfaces has significant negative economic effects. The aim of this study was to find a simple procedure to decrease the Pseudomonas aeruginosa biofilm formation in a water environment by using different food waste biological materials as signal molecule adsorbents. The selected biomaterials did not reduce the cell growth but affected biofilm formation. Promising biomaterials were magnetically modified in order to simplify manipulation and facilitate their magnetic separation. The best biocomposite, magnetically modified spent grain, exhibited substantial adsorption of signal molecules and decreased the biofilm formation. These results suggest that selected food waste materials and their magnetically responsive derivatives could be applied to solve biofilm problems in water environment.