Initial Biofilm Development Research Articles

Metallo-β-lactamases producing Pseudomonas aeruginosa and the molecular mechanism of drug resistance variants

BackgroundMetallo-β-lactamases (MBLs) type carbapenemases are produced by pathogenic Pseudomonas spp. and exhibit carbapenemase activity. The study will look into drug resistance and the molecular mechanisms of drug-resistant Pseudomonas aeruginosa variants. MethodsA total of 74 P. aeruginosa strains were isolated from urine, pus, sputum, blood, throat swab, Foley’s catheter, and nasal swab. The isolates were screened for antibiotic susceptibility and the identified MDR strains were further tested for β-lactamase production. Multiplex PCR was used to identify the presence of mcr-1 and blaNDM-1 genes in MDR organisms. The minimum inhibitory concentration for ceftazidime and colistin was also determined, in addition to the biofilm inhibitor activity. Confocal microscopy was used to determine the production of biofilms. ResultsThe isolated P. aeruginosa strains exhibited antibiotic resistance to aminoglycosides (amikacin and gentamicin). Fifty three percent of the isolated P. aeruginosa strains produced metallo-β-lactamase and the remaining isolates were non-metallo-β-lactamase type (46.8 %) (p < 0.0001). The MIC value of β-lactamase producers against colistin ranges from 0.5 µg/mL to 6 µg/mL. The MDR bacteria exhibited mcr-1 and blaNDM−1 genes. The MDR P. aeruginosa strain treated with colistin and ceftazidime inhibited initial biofilm formation. These combination of antibiotics effectively prevented initial biofilm development than individual antibiotics (p < 0.001). ConclusionsThe current analysis detected MDR among P. aeruginosa isolates that carried drug-resistant genes.

Dihydrothiazolo ring-fused 2-pyridone antimicrobial compounds treat Streptococcus pyogenes skin and soft tissue infection.

We have developed GmPcides from a peptidomimetic dihydrothiazolo ring-fused 2-pyridone scaffold that has antimicrobial activities against a broad spectrum of Gram-positive pathogens. Here, we examine the treatment efficacy of GmPcides using skin and soft tissue infection (SSTI) and biofilm formation models by Streptococcus pyogenes. Screening our compound library for minimal inhibitory (MIC) and minimal bactericidal (MBC) concentrations identified GmPcide PS757 as highly active against S. pyogenes. Treatment of S. pyogenes biofilm with PS757 revealed robust efficacy against all phases of biofilm formation by preventing initial biofilm development, ceasing biofilm maturation and eradicating mature biofilm. In a murine model of S. pyogenes SSTI, subcutaneous delivery of PS757 resulted in reduced levels of tissue damage, decreased bacterial burdens, and accelerated rates of wound healing, which were associated with down-regulation of key virulence factors, including M protein and the SpeB cysteine protease. These data demonstrate that GmPcides show considerable promise for treating S. pyogenes infections.

FliA-Dependent Surface Macromolecules Promote Initial Biofilm Development of Escherichia coli by Influencing the Bacterial Surface Properties

FliA is an important regulatory component for the synthesis of surface macromolecules which are involved in motility and biofilm development of Escherichia coli. In this study, the roles of FliA-dependent surface macromolecules in E. coli surface tension, surface heterogeneity and surface roughness, and initial biofilm development consisting of reversible and irreversible adhesion were investigated using E. coli MG1655 wild-type strain and fliA gene deleted mutant strain. Negative Gibbs free energy change values calculated using bacterial surface tensions obtained by a spectrophotometric method showed that both wild-type and mutant cells in water can reversibly adhere to the surface of the model solid, silicon nitride (Si3N4). The calculations further showed that bacterial reversible auto-adhesion and co-adhesion were also thermodynamically favorable. In comparison, the reversible adhesion and auto-adhesion capacities of wild-type cells were higher than the mutant cells. Direct measurements by atomic force microscopy (AFM) and thorough analysis of the recorded adhesion data showed that the irreversible adhesion strength of wild-type cells to Si3N4 in water was at least 2.0-fold greater than that of the mutants due to significantly higher surface heterogeneity resulting in higher surface roughness for the wild-type cells compared to those obtained for the mutants. These results suggest that strategies aimed at preventing E. coli biofilm development should also consider a combined method, such as modifying the surface of interest with a bacterial repellent layer and targeting the FliA and FliA-dependent surface macromolecules to reduce both reversible and irreversible bacterial adhesion and hence the initial biofilm development of E. coli.

Identification of steel corrosion associated with sulfate‐reducing bacteria by electrochemical noise technique

AbstractDeterioration of steel structures in natural waters can result from microbiologically influenced corrosion (MIC) such as that caused by sulfate‐reducing bacteria (SRB). Corrosion pits associated with MIC have been recently observed in submerged steel bridge piles and there is renewed interest to assess their deterioration. Conventional electrochemical techniques to identify MIC have been complicated due to the effects of the surface films and the mechanism for charge transfer by the bacteria on the steel surface. An electrochemical noise (EN) technique to identify steel corrosion in an aqueous solution has been developed and the method ideally can identify the onset of local pitting, but complications and limitations relating to data acquisition, filtering, and interpretation exist. EN analysis was shown to differentiate SRB and corrosion activity including initial biofilm development, pitting corrosion development, and diminution of SRB activity. Electrochemical behavior, environmental characteristics, SRB activity, and corrosion modality provided consistent correlation to EN and localized corrosion development.

Initial Formation and Accumulation of Manganese Deposits in Drinking Water Pipes: Investigating the Role of Microbial-Mediated Processes

Microbial Mn(II) oxidation occurs in areas with insufficient disinfectants in drinking water distribution systems. However, the overall processes of microbial-mediated Mn deposit formation are unclear. This research investigated the initial Mn(II) oxidation, deposit accumulation, and biofilm development in pipe loops fed with nondisinfected finished water for 300 days. The results show that it took 20 days for microbial Mn(II) oxidation and deposition to be initiated visibly in new pipes continuously receiving 100 μg/L Mn(II). Once started, the deposit accumulation accelerated. A pseudo-first-order kinetic model could simulate the disappearance of Mn(II) in well-mixed pipe loop water. The observed rate constant reached 2.81 h-1 [corresponding to a Mn(II) half-life of 0.25 h] after 136 days of operation. Without oxygen, Mn(II) in the water also decreased rapidly to 1.0 μg/L through adsorption to deposits, indicating that after the initial microbial formation of MnOx, subsequent MnOx accumulation was attributable to a combination of microbial and physicochemical processes. Compared to the no-Mn condition, Mn(II) input resulted in 1 order of magnitude increase in biofilm formation. This study sheds light on the increasingly rapid processes of Mn accumulation on the inner surfaces of water pipes resulting from the biological activity of Mn(II)-oxidizing biofilms and the build-up of MnOx with strong adsorption capacity.

Bacterial community structure of early-stage biofilms is dictated by temporal succession rather than substrate types in the southern coastal seawater of India.

Bacterial communities colonized on submerged substrata are recognized as a key factor in the formation of complex biofouling phenomenon in the marine environment. Despite massive maritime activities and a large industrial sector in the nearshore of the Laccadive Sea, studies describing pioneer bacterial colonizers and community succession during the early-stage biofilm are scarce. We investigated the biofilm-forming bacterial community succession on three substrata viz. stainless steel, high-density polyethylene, and titanium over 15 days of immersion in the seawater intake area of a power plant, located in the southern coastal region of India. The bacterial community composition of biofilms and peripheral seawater were analyzed by Illumina MiSeq sequenced 16S rRNA gene amplicons. The obtained metataxonomic results indicated a profound influence of temporal succession over substrate type on the early-stage biofilm-forming microbiota. Bacterial communities showed vivid temporal dynamics that involved variations in abundant bacterial groups. The proportion of dominant phyla viz. Proteobacteria decreased over biofilm succession days, while Bacteroidetes increased, suggesting their role as initial and late colonizers, respectively. A rapid fluctuation in the proportion of two bacterial orders viz. Alteromonadales and Vibrionales were observed throughout the successional stages. LEfSe analysis identified specific bacterial groups at all stages of biofilm development, whereas no substrata type-specific groups were observed. Furthermore, the results of PCoA and UPGMA hierarchical clustering demonstrated that the biofilm-forming community varied considerably from the planktonic community. Phylum Proteobacteria preponderated the biofilm-forming community, while the Bacteroidetes, Cyanobacteria, and Actinobacteria dominated the planktonic community. Overall, our results refute the common assumption that substrate material has a decisive impact on biofilm formation; rather, it portrayed that the temporal succession overshadowed the influence of the substrate material. Our findings provide a scientific understanding of the factors shaping initial biofilm development in the marine environment and will help in designing efficient site-specific anti-biofouling strategies.

Low concentration of Tween-20 enhanced the adhesion and biofilm formation of Acidianus manzaensis YN-25 on chalcopyrite surface

Although Tween-20 was used as an important catalyst to increase chalcopyrite bioleaching rate by acidophiles, the effect of Tween-20 on initial adhesion and biofilm development of acidophiles on chalcopyrite has not been explored until now. Herein, the role of Tween-20 in early attachment behaviors and biofilm development by Acidianus manzaensis strain YN-25 were investigated by adhesion experiments, adhesion force measurement, visualization of biofilm assays and a series of analyses including extended Derjaguin Landau Verwey Overbeek (DLVO) theory, scanning electron microscopy (SEM) and X-ray photoelectron spectroscopy (XPS). The bacterial adhesion experiments showed that 2 mg/L of Tween-20 increased the adhesion percentage (by 8%) of A. manzaensis YN-25. Tween-20 could promote the early adhesion of A. manzaensis YN-25 by changing the Lewis acid-base interaction and electrostatic force to increase total interaction energy and adhesion force. Besides, the functional groups on the surface of cells (carboxyl, hydroxyl and amino functional groups) contributed to the adhesion of A. manzaensis YN-25 on chalcopyrite. Furthermore, the promotion of biofilm formation by Tween-20 was mainly attributed to the reduction of S0 passivation layer formation and complexing more Fe3+ on chalcopyrite surface, contributing to the erosion of chalcopyrite and creating more corrosion pits. Live/dead staining showed low live/dead ratio (ranged from 0.35 to 1.32) during the biofilm development process. This report offers a better understanding of the effects of Tween-20 on attachment and biofilm development of acidophilic microorganisms and would lay a theoretical foundation for the better application of catalyst in bioleaching.

Effectivity of homecare and professional biofilm removal procedures on initial supragingival biofilm on laser-microtextured implant surfaces in an ex vivo model

BackgroundThe aim of the current study was the evaluation of initial biofilm adhesion and development on laser-microtextured implant collar surfaces and the examination of effectivity of different biofilm management methods.MethodsInitial biofilm formation was investigated on hydrophobic machined and laser-microtextured (Laser-Lok) titanium surfaces and hydrophobic machined and laser-microtextured (Laser-Lok) titanium aluminium vanadium surfaces and compared to hydrophobic smooth pickled titanium surfaces, hydrophilic smooth and acid etched titanium surfaces, hydrophobic sandblasted large grid and acid etched titanium surfaces (titanium Promote) via erythrosine staining and subsequent histomorphometrical analysis and scanning electron microscopic investigations. After decontamination procedures, performed via tooth brushing and glycine powder blasting, clean implant surface was detected via histomorphometrical analysis.ResultsAfter 24 h mean initial plaque area was detected in the following descending order: smooth pickled titanium > titanium Promote > hydrophilic smooth and acid etched titanium > Laser-Lok titanium > Laser-Lok titanium aluminium vanadium. The same order was determined after 48 h of biofilm formation. After glycine powder blasting all samples depicted almost 100% clean implant surface. After tooth brushing, Laser-Lok titanium (67.19%) and Laser-Lok titanium aluminium vanadium (69.80%) showed significantly more clean implant surface than the other structured surfaces, hydrophilic smooth and acid etched titanium (50.34%) and titanium Promote (33.89%). Smooth pickled titanium showed almost complete clean implant surface (98.84%) after tooth brushing.ConclusionsBoth Laser-Lok surfaces showed less initial biofilm formation after 24 and 48 h than the other implant surfaces. In combination with the significant higher clean implant surfaces after domestic decontamination procedure via tooth brushing, both Laser-Lok surfaces could be a candidate for modified implant and abutment designs, especially in transmucosal areas.

Diversity and structure of microbial biofilms on microplastics in riverine waters of the Pearl River Delta, China

Riverine runoff is a significant transport pathway for microplastics (MPs) discharged from land-based sources to marine environments where MPs accumulate. Knowledge of riverine MP-associated biofilms will improve the understanding of the fate and potential effects of MPs in marine environments. This study aimed to characterize the microbial biofilms colonizing MPs in the riverine water of the Pearl River Delta, China, and identify the seasonal, geographical and environmental influences on MP-associated communities. We sampled MPs and the surrounding surface water from eight outlets in three seasons and analyzed their microbial communities by Illumina sequencing of the 16S rRNA gene libraries. Across all sampling seasons and locations, abundant MP-colonizing taxa belonged to the phylum Proteobacteria, which suggested initial biofilm development on those MPs. The structure and composition of MP-attached microbial communities varied with respect to season and location, and the microbial diversity of the MP-associated biofilm communities decreased in June compared with that in the April and November sampling events. Opportunistic pathogens of the genus Acinetobacter were significantly enriched on the MP surfaces for all sampling events. Among the 15 environmental variables examined, the main drivers of MP-associated biofilm community composition included IC, alkalinity, TOC, TDS, Cl−, NO3−, NO2− and pH. This study provides an insight into the environmental factors that shape microbial biofilm colonization on MPs in estuary environments and a further understanding of the structure, diversity and ecological roles of MP-associated communities.

Flow and Permeability Evolution during Microbial Sulfate Reduction and Inhibition in Fractured Rocks

Subsurface biological processes, such as biofilm development, modify flow and permeability in fractured rocks, greatly impacting energy production or treatment efficiencies. This study aims to understand biological–hydrological interactions at a bench scale during the progression and treatment of souring (microbially mediated sulfide production). Few bench-scale studies investigate the role of a biofilm on the flow and permeability evolution, sulfidogensis, and nitrate treatment efficacy in fractured rocks. Our experiment consisted of three sandstone columns that represent differing fracture characteristics due to the mode of fracture initiation: one column with no fracture (as a control), one column with a sawcut fracture, and a third column with a fracture induced by Brazilian loading (tensile). We seek to understand the effects of the biofilm-permeability feedback on flow and nutrient transport characteristics of fractured rocks; specifically, we (1) demonstrate how fracture geometries impact the development of the biomass-permeability feedback within the rock fractures and (2) observe the souring trajectory and effects of nitrate treatment. Observed permeability trends demonstrated that bioclogging modified the flow properties of fractured columns such that they became hydrologically similar to those of the control column. While fractures were initially the main sites of sulfate reduction, when fractures were clogged, the flow in the fractured columns transitioned from a fracture-dominated flow to a matrix-dominated flow, impacting the delivery of an electron acceptor/donor to the microbial population, reducing sulfate reduction rates. Experimental data also demonstrated two distinct stages in the biofilm-permeability development. During the initial biofilm development stage, the growing microbial population had increased reaction rates but decreased permeability, i.e., a negative correlation between reaction rates and permeability. In the later stage, when the biofilm had clogged the columns, a series of biofilm shedding and regrowth directly led to reopening and clogging of the flow channels, affecting microbial accessibility to limiting nutrients. As such, a positive correlation between reaction rates and permeability was observed in this later stage. Post experimental measurements of surface elevations of the fractured surfaces revealed that surface elevations in the sawcut column were lower and more evenly distributed than the surface elevations in the tensile column where the more unevenly fractured surfaces potentially better supported the microbial establishment.

Quantitative analysis of the surficial and adhesion properties of the Gram-negative bacterial species Comamonas testosteroni modulated by c-di-GMP

Cyclic diguanylate monophosphate (c-di-GMP) is a ubiquitous intracellular secondary messenger which governs the transition from a bacterial cell’s planktonic state to biofilm formation by stimulating the production of a variety of exopolysaccharide material by the bacterial cell. A range of genes involved in c-di-GMP signaling in the Gram-negative species Comamonas testosteroni have been identified previously, yet the physical-chemical properties of the produced extracellular polymeric substances (EPS) and the bacterial adhesion characteristics regulated by c-di-GMP are not well understood. Here, we modulated the in vivo c-di-GMP levels of Comamonas testosteroni WDL7 through diguanylate cyclase (YedQ) and phosphodiesterase (YhjH) gene editing. The strains and their adhesion properties were characterized by Fourier-transform infrared and two-dimensional correlation spectroscopy analysis (FTIR-2D CoS), contact angle and zeta potential measurements, atomic force microscopy (AFM) and extended-Derjaguin-Landau-Verwey-Overbeek (ExDLVO) analysis. Our results show that high c-di-GMP levels promoted the secretion of long-chain hydrophobic and electroneutral extracellular polysaccharides and proteins. The protein molecules on WDL7/pYedQ2 promoted the bacterial self-aggregation and adhesion onto negatively charged surfaces. In contrast, the reduction of intracellular c-di-GMP concentrations resulted in a nearly 80 % decrease in the adhesion of bacterial cells, although little change in the surface hydrophobicity or surface charge properties were observed for these cells relative to the wild type. These results indicate that the reduced adsorption of WDL7/YhjH that we observed may be caused by the flagellum-accelerated mobility at low c-di-GMP concentrations. Taken together, these results improve our mechanistic understanding of the effects of c-di-GMP in controlling bacterial physical-chemical properties and initial biofilm development.

Feeding the Building Plumbing Microbiome: The Importance of Synthetic Polymeric Materials for Biofilm Formation and Management

The environmental conditions in building plumbing systems differ considerably from the larger distribution system and, as a consequence, uncontrolled changes in the drinking water microbiome through selective growth can occur. In this regard, synthetic polymeric plumbing materials are of particular relevance, since they leach assimilable organic carbon that can be utilized for bacterial growth. Here, we discuss the complexity of building plumbing in relation to microbial ecology, especially in the context of low-quality synthetic polymeric materials (i.e., plastics) and highlight the major knowledge gaps in the field. We furthermore show how knowledge on the interaction between material properties (e.g., carbon migration) and microbiology (e.g., growth rate) allows for the quantification of initial biofilm development in buildings. Hence, research towards a comprehensive understanding of these processes and interactions will enable the implementation of knowledge-based management strategies. We argue that the exclusive use of high-quality materials in new building plumbing systems poses a straightforward strategy towards managing the building plumbing microbiome. This can be achieved through comprehensive material testing and knowledge sharing between all stakeholders including architects, planners, plumbers, material producers, home owners, and scientists.

Analyzing the inhibitory effect of metabolic uncoupler on bacterial initial attachment and biofilm development and the underlying mechanism

Metabolic uncouplers inhibit biofilm and biofouling formation in membrane bioreactor (MBR) systems, which have been considered as a potential biofouling control alternative. To better understand the inhibitory mechanism of uncoupler on biofouling, this study investigated the impact of the uncoupler 3, 3′, 4′, 5-tetrachlorosalicylanilide (TCS) on biofilm formation of B. subtilis in different development stages. Significant reductions in both the initial bacterial attachment stage and the subsequent biofilm development stage were caused by TCS at 100 μg/L. The motility of B. subtilis in semisolid medium was inhibited by TCS, which explicitly explained the reduction in initial bacterial attachment. Meanwhile, a reduction of extracellular polymeric substance (EPS) secretion owing to TCS suggested why biofilm development was suppressed. In addition, the fluorescent materials in tight-bound EPS (TB-EPS) and loose-bound EPS (LB-EPS) of Bacillus subtilis cultured in different TCS concentrations were distinguished and quantified by three-dimensional excitation-emission matrix (EEM) fluorescence spectroscopy coupled with parallel factor analysis (PARAFAC). The results of this study suggested that the biofilm inhibitory mechanism of the uncoupler was both a inhibition in bacterial motor ability and a reduction in EPS secretion.

Quorum sensing signaling distribution during the development of full-scale municipal wastewater treatment biofilms

Acylated homoserine lactone (AHL)-mediated quorum sensing (QS) is ecologically important in multi-species systems in laboratory-scale studies; however, little is known about QS in the biofilm formation process in full-scale wastewater treatment plants, which is driven by multiple environmental variables. Here, a model integrated fixed-film-activated sludge system was employed in full-scale municipal wastewater treatment plant to investigate the AHL distribution during the biofilm development process in response to variable environmental factors. The whole biofilm development process can be divided into three phases: initial biofilm attachment process (week 1 to 3), biofilm development and mature phase (week 4 to 6), and biofilm detachment and reformation process (week 7 to 17). N-decanoyl-DL-homoserine lactone (C10-HSL) and N-dodecanoyl-DL-homoserine lactone (C12-HSL) presented high concentrations during the biofilm formation process, which was closely related with the biofilm initial attachment process. The AHL concentration in biofilms was higher than in activated sludge. During the initial attachment process, tryptophan and protein-like substances related to biological substance were strongly positively correlated with all detected AHL concentrations (p < 0.05). Three environmental variables (total nitrogen, pH, and Na+) were closely related to AHL distribution in municipal wastewater biofilms. High wastewater pH was found to contribute to a low AHL concentration. AHLs in the biofilm were significantly (p < 0.01) influenced by the concentration of Na+, and higher concentrations of Na+ (10.84–18.58 mg/L) in wastewater treatment plants potentially contribute to the biofilm formation processes. In addition, bacteria with nitrogen removal ability showed QS functionality. The results of this study indicate that AHL-based regulation of tryptophan and protein-like substances related to biological substance production was significantly influenced by the surrounding chemical environment, which has been underestimated in previous studies. AHL-mediated QS potentially suggests a novel solution for the advanced AHL-based regulation of the biofilm development processes.

Continuous shear stress alters metabolism, mass-transport, and growth in electroactive biofilms independent of surface substrate transport

Electroactive bacteria such as Geobacter sulfurreducens and Shewanella onedensis produce electrical current during their respiration; this has been exploited in bioelectrochemical systems. These bacteria form thicker biofilms and stay more active than soluble-respiring bacteria biofilms because their electron acceptor is always accessible. In bioelectrochemical systems such as microbial fuel cells, corrosion-resistant metals uptake current from the bacteria, producing power. While beneficial for engineering applications, collecting current using corrosion resistant metals induces pH stress in the biofilm, unlike the naturally occurring process where a reduced metal combines with protons released during respiration. To reduce pH stress, some bioelectrochemical systems use forced convection to enhance mass transport of both nutrients and byproducts; however, biofilms’ small pore size limits convective transport, thus, reducing pH stress in these systems remains a challenge. Understanding how convection is necessary but not sufficient for maintaining biofilm health requires decoupling mass transport from momentum transport (i.e. fluidic shear stress). In this study we use a rotating disc electrode to emulate a practical bioelectrochemical system, while decoupling mass transport from shear stress. This is the first study to isolate the metabolic and structural changes in electroactive biofilms due to shear stress. We find that increased shear stress reduces biofilm development time while increasing its metabolic rate. Furthermore, we find biofilm health is negatively affected by higher metabolic rates over long-term growth due to the biofilm’s memory of the fluid flow conditions during the initial biofilm development phases. These results not only provide guidelines for improving performance of bioelectrochemical systems, but also reveal features of biofilm behavior. Results of this study suggest that optimized reactors may initiate operation at high shear to decrease development time before decreasing shear for steady-state operation. Furthermore, this biofilm memory discovered will help explain the presence of channels within biofilms observed in other studies.

Green fabrication of iron oxide nanoparticles using grey mangrove Avicennia marina for antibiofilm activity and in vitro toxicity

The aim of the present study is a biogenic synthesis of iron oxide nanoparticles (FeO-NPs) using grey mangrove Avicennia marina to control marine and pathogenic biofilm forming bacteria. Initially, the synthesized nanoparticles were characterized by UV-visible spectrometer, scanning electron microscope and transmission electron microscope for size and shape, Edax analysis for elemental confirmation, zeta potential for stability, X-ray diffraction for structure and Fourier transform infrared spectroscopy for functional group analysis. Further, the antibiofilm activity of FeO-NPs were inhibited the initial attachment and biofilm development of primary biofilm forming bacterial strains Escherichia coli, Pseudomonas aeruginosa and Staphylococcus aureus. Almost 72% of quorum sensing factors of P. aeruginosa were impeded by 200 µg/ml of FeO-NPs, 63% and 46% for S. aureus and E. coli respectively. The FeO-NPs also decrease the cell surface hydrophobicity of E. coli, P. aeruginosa and S. aureus from 16% to 9%, 19% to 11% and 15% to 11% respectively. Moreover, the FeO-NPs inhibit the production of exopolysaccharide in E. coli, P. aeruginosa and S. aureus from 90% to 69%, 92% to 65% and 86% to 60% respectively. Further, the FeO-NPs also showed less toxicity against human HBL100 cells using the MTT assay. In conclusion, the biogenic FeO-NPs could be used as a potential antibiofilm agent against marine and medical pathogenic biofilm forming bacteria.

Disentangling settlement responses to nutrient-rich contaminants: Elevated nutrients impact marine invertebrate recruitment via water-borne and substrate-bound cues

Anthropogenic contaminants, including nutrient enrichment, frequently alter environmental conditions in marine systems and affect the development of communities on hard-substrata. Biofilms can influence the settlement of marine invertebrates and hence impact on the structure of fouling communities. Few studies have examined bacteria, invertebrates and nutrient-rich contaminants in concert, with none yet to examine the effects of nutrient-rich contaminants on both biofilms and the recruitment of sessile invertebrate communities in-situ to ascertain the mechanistic basis behind observed impacts. Biofilm treatments were allowed to develop under manipulated environmental conditions of either ambient or enriched nutrient levels. Enrichment conditions were elevated via slow-release fertiliser and invertebrate recruitment was prevented during initial biofilm development. Biofilm treatments (including a no film control) were then subject to either ambient or enriched water-borne nutrients (in a fully-factorial design) during a period of invertebrate colonisation in the field. Effects of nutrient-rich contaminants on invertebrate recruitment were observed as changes to community composition and the abundances of taxonomic groups. Communities on no biofilm control treatments differed from those with pre-developed biofilms. Naturally developed biofilms promoted recruitment by all organisms, except barnacles, which preferred nutrient-enriched biofilms. Water-borne nutrients increased the recruitment of ascidians and barnacles, but suppressed bryozoan, serpulid polychaete and sponge recruitment. The direct and indirect impacts observed on biofilm and invertebrate communities suggest that increasing nutrient levels via nutrient-rich contaminants will result in structural community shifts that may ultimately impact ecosystem functioning within estuaries.

In situ monitoring of wastewater biofilm formation process via ultrasonic time domain reflectometry (UTDR)

Biofilm development plays an important role in facilitating wastewater treatment. The ultrasonic time domain reflectometry (UTDR) is presented for the first time as a tool to assess the initial biofilms development process on bio-carriers. The experiments were carried out with bio samples gathered from practical municipal wastewater and industrial wastewater, respectively. The in-situ and non-invasive UTDR technique was applied to visualize and evaluate the biofilm development process on slices through using the 2D and 3D wavelet analysis by a false color scale. Especially, the distinguished biofilms thickness was observed during the initial biofilm development process via a differential signal, and the relatively dense degree of biofilm were also obtained at the same time. The UTDR measurement could distinguish the initial adherence, reversible adhesion and irreversible adhesion during the initial biofilm formation process. In addition, the UTDR response correlates well with the off-line measurements of the biofilm thickness via an atomic force microscope and optical coherence tomography, suggesting that UTDR-based characterization is a useful tool for in-situ investigating the dynamic processes of predefined biofilm development used for wastewater treatment.

Start-up of an anaerobic fluidized bed reactor treating synthetic carbohydrate rich wastewater

The present work studied the start-up process of a mesophilic (37 ± 2 °C) anaerobic fluidized bed reactor (AFBR) operated at a hydraulic retention time (HRT) of 20 days using synthetic carbohydrate rich wastewater. Anox Kaldness-K1 carriers were used as biofilm carrier material. The reactor performance and biofilm formation were evaluated during the process. The start-up process at lower liquid recirculation flow rate enhanced the biofilm formation and reactor performance. The organic substrate composition had a major impact on early colonization of methanogenic archaea onto the surface of the Kaldness carriers during the start-up process. Specific organic substrates favouring the growth of methanogenic archaea, such as acetate, are preferred in order to facilitate the subsequent biofilm formation and AFBR start-up. The supply of ‘bio-available’ nutrients and trace elements, in particular iron, had an important role on optimal methanogenic activity and speeding-up of the biofilm development on the Kaldness carriers. This paper provides possible strategies to optimize the various operational parameters that influence the initial biofilm formation and development in an AFBR and similar high rate anaerobic reactors, hence can be used to reduce the long time required for process start-up.

Quorum quenching bacteria isolated from the sludge of a wastewater treatment plant and their application for controlling biofilm formation.

Bacteria recognize changes in their population density by sensing the concentration of signal molecules, N-acyl-homoserine lactones (AHLs). AHL-mediated quorum sensing (QS) plays a key role in biofilm formation, so the interference of QS, referred to as quorum quenching (QQ), has received a great deal of attention. A QQ strategy can be applied to membrane bioreactors (MBRs) for advanced wastewater treatment to control biofouling. To isolate QQ bacteria that can inhibit biofilm formation, we isolated diverse AHL-degrading bacteria from a laboratory-scale MBR and sludge from real wastewater treatment plants. A total of 225 AHLdegrading bacteria were isolated from the sludge sample by enrichment culture. To identify the enzyme responsible for AHL degradation in QQ bacteria, AHL-degrading activities were analyzed using cell-free lysate, culture supernatant, and whole cells. Afipia sp. and Acinetobacter sp. strains produced the intracellular QQ enzyme, whereas Pseudomonas sp. and Micrococcus sp. produced the extracellular QQ enzyme that was most likely to produce AHLacylase. AHL-degrading activity was observed in whole-cell assay with the Microbacterium sp. and Rhodococcus sp. strains. There has been no report for AHL-degrading capability in the case of Streptococcus sp. and Afipia sp. strains. Finally, inhibition of biofilm formation by isolated QQ bacteria or enzymes was observed on glass slides and 96-well microtiter plates using crystal violet staining. QQ strains or enzymes not only inhibited initial biofilm development but also reduced established biofilms.