Fatty acids of lipid fractions in extracellular polymeric substances of activated sludge flocs

Impact of weathered and virgin polyethylene terephthalate (PET) micro- and nanoplastics on growth dynamics and the production of extracellular polymeric substances (EPS) of microalgae

The ever-increasing plastic waste accumulation in the marine environment necessitates a deeper understanding of microalgae interactions with micro- and nanoplastics (MNP), and the role of extracellular polymeric substances (EPS). EPS, known for its adhesive properties and produced as an algal stress response, may facilitate aggregation of both algae and MNPs, thereby impacting ecological and hydrodynamic processes such as the trophic transfer or vertical transport of MNPs. Moreover, gaining a deeper understanding of the impact of weathering processes on the potential toxicological effects of plastic particles, and the comparative significance of plastic-specific effects relative to those of naturally occurring particles such as kaolin clay, is imperative. Therefore, this study investigated the impact of fragmented, polydisperse virgin polyethylene terephthalate (PET, Daverage = 910 nm) and weathered PET (Daverage = 1700 nm) on the growth and the production of EPS of Rhodomonas salina. Algae were exposed to a range of low MNP concentrations (10, 100 and 1000 and 10,000 MNPs ml-1) for 11 days. A natural particle control (kaolin, Daverage = 1600 nm) was deployed to differentiate particle effects from plastic effects. It was observed that exposure to both weathered PET and virgin PET resulted in initially increased growth rates (7.80 % and 7.28 % respectively), followed by significant decreases in algae cell density (-30.1 % and -11.2 % respectively). Furthermore, exposure to weathered PET caused a simultaneous elevation in cellular EPS production (76.51 %). The effects of plastics were significantly larger than the effect of kaolin. Also, the observed effects were amplified by the weathering of the plastics. These observations underscore the interactions between particle type, age and concentration, and their distinct impacts on algae density and growth inhibition. The observations indicate a role for EPS as an algal protection mechanism, potentially affecting the environmental fate of MNP - microalgae aggregates.

The impact of methylparaben and chlorine on the architecture of Stenotrophomonas maltophilia biofilms

The biofilm architecture is significantly influenced by external environmental conditions. Biofilms grown on drinking water distribution systems (DWDS) are exposed to environmental contaminants, including parabens, and disinfection strategies, such as chlorine. Although changes in biofilm density and culturability from chemical exposure are widely reported, little is known about the effects of parabens and chlorine on biofilm morphology and architecture. This is the first study evaluating architectural changes in Stenotrophomonas maltophilia colony biofilms (representatives of bacterial communities presented in DWDS) induced by the exposure to methylparaben (MP) at environmental (15 μg/L) and in-use (15 mg/L) concentrations, and chlorine at 5 mg/L, using widefield epi-fluorescence mesoscopy with Mesolens. The GFP fluorescence of colony biofilms allowed the visualization of internal structures and Nile Red fluorescence permitted the inspection of the distribution of lipids. Our data show that exposure to MP triggers physiological and morphological adaptation in mature colony biofilms by increasing the complexity of internal structures, which may confer protection to embedded cells from external chemical molecules. These architectural modifications include changes in lipid distribution as an adaptive response to MP exposure. Although chlorine exposure affected colony biofilm diameter and architecture, the colony roundness was completely affected by the simultaneous presence of MP and chlorine. This work is pioneer in using Mesolens to highlight the risks of exposure to emerging environmental contaminants (MP), by affecting the architecture of biofilms formed by drinking water (DW) bacteria, even when combined with routine disinfection strategies.

Studying microbially induced corrosion on glass using ToF-SIMS

Microbially induced corrosion (MIC) is an emerging topic that has huge environmental impacts, such as long-term evaluation of microbial interactions with radioactive waste glass, environmental cleanup and disposal of radioactive material, and weathering effects of microbes. Time-of-flight secondary ion mass spectrometry (ToF-SIMS), a powerful mass spectral imaging technique with high surface sensitivity, mass resolution, and mass accuracy, can be used to study biofilm effects on different substrates. Understanding how to prepare biofilms on MIC susceptible substrates is critical for proper analysis via ToF-SIMS. We present here a step-by-step protocol for preparing bacterial biofilms for ToF-SIMS analysis, comparing three biofilm preparation techniques: no desalination, centrifugal spinning (CS), and water submersion (WS). Comparisons of two desalinating methods, CS and WS, show a decrease in the media peaks up to 99% using CS and 55% using WS, respectively. Proper desalination methods also can increase biological signals by over four times for fatty acids using WS, for example. ToF-SIMS spectral results show chemical compositional changes of the glass exposed in a Paenibacillus polymyxa SCE2 biofilm, indicating its capability to probe microbiologically induced corrosion of solid surfaces. This represents the proper desalination technique to use without significantly altering biofilm structure and substrate for ToF-SIMS analysis. ToF-SIMS spectral results showed chemical compositional changes of the glass exposed by a Paenibacillus bacterial biofilm over 3-month inoculation. Possible MIC products include various phosphate phase molecules not observed in any control samples with the highest percent increases when experimental samples were compared with biofilm control samples.

An automated contact model for transmission of dry surface biofilms of Acinetobacter baumannii in healthcare

BACKGROUND

Dry surface biofilms (DSBs) have been recognized across environmental and equipment surfaces in hospitals and could explain how microbial contamination can survive for an extended period and may play a key role in the transmission of hospital-acquired infections. Despite little being known on how they form and proliferate in clinical settings, DSB models for disinfectant efficacy testing exist.

AIM

In this study we develop a novel biofilm model to represent formation within hospitals, by emulating patient to surface interactions.

METHODS

The model generates a DSB through the transmission of artificial human sweat (AHS) and clinically relevant pathogens using a synthetic thumb capable of emulating human contact. The DNA, glycoconjugates and protein composition of the model biofilm, along with structural features of the micro-colonies was determined using fluorescent stains visualized by epifluorescence microscopy and compared with published clinical data.

RESULTS

Micrographs revealed the heterogeneity of the biofilm across the surface; and reveal protein as the principal component within the matrix, followed by glycoconjugates and DNA. The model repeatably transferred trace amounts of micro-organisms and AHS, every 5 min for up to 120 h on to stainless-steel coupons to generate a biofilm model averaging 1.16 × 103 cfu/cm2 falling within the reported range for clinical DSB (4.20 × 102 to 1.60 × 107 bacteria/cm2).

CONCLUSION

Our in vitro DSB model exhibits many phenotypical characteristics and traits to those reported in situ. The model highlights key features often overlooked and the potential for downstream applications such as antibiofilm claims using more realistic microbial challenges.

Bacterial extracellular polymeric substances: Biosynthesis and interaction with environmental pollutants

Extracellular polymeric substances (EPS) are highly hydrated matrices produced by bacteria, containing various polymers such as polysaccharides, proteins, lipids, and DNA. Extracellular polymer concentrations, ions, and functional groups provide physical stability to the EPS. Constituents of EPS form the three-dimensional architecture and help acquire nutrition for the bacteria. Structural and functional diversity of the extracellular polymer depends on the specific glycosyltransferases, polymerase and transporter proteins. These enzymes are encoded by specific genes present in operons such as crd, alg, wca, and gum reported in Agrobacterium, Pseudomonas, Enterobacteriaceae, and Xanthomonas. The operons regulate the biosynthesis of extracellular polymers such as curdlan, alginate, colonic acid, and xanthan, respectively. Various functional groups in the EPS, such as carbonyl, hydroxyl, phosphoryl, and amide, provide the sorption site for interaction with environmental pollutants. Hydrophobic interactions and coordinate bonds mainly dominate the binding of EPS with environmental pollutants. EPS binds, emulsifies, and solubilizes the organic compounds, enhancing the degradation process. EPS binds with heavy metals through complexation, surface adsorption, precipitation, and ion exchange mechanisms. The biodegradability efficiency and nontoxicity properties of EPS make it an excellent biopolymer for decontaminating environmental pollutants. This review summarizes an overview of the biosynthetic mechanisms and interaction of the bacterial extracellular polymer with environmental pollutants. Interaction mechanisms of pollutants with EPS and EPS-mediated bioremediation will help develop removal applications. Moreover, understanding the genes responsible for EPS production, and implementation of new genetic methodology can be helpful for the enhanced biosynthesis of EPS to control pollution by sequestrating more environmental pollutants.

Chemical Imaging of Pharmaceuticals in Biofilms for Wastewater Treatment Using Secondary Ion Mass Spectrometry

The occurrence of pharmaceuticals in the aquatic environment is a global water quality challenge for several reasons, such as deleterious effects on ecological and human health, antibiotic resistance development, and endocrine-disrupting effects on aquatic organisms. To optimize their removal from the water cycle, understanding the processes during biological wastewater treatment is crucial. Time-of-flight secondary ion mass spectrometry imaging was successfully applied to investigate and analyze the distribution of pharmaceuticals as well as endogenous molecules in the complex biological matrix of biofilms for wastewater treatment. Several compounds and their localization were identified in the biofilm section, including citalopram, ketoconazole, ketoconazole transformation products, and sertraline. The images revealed the pharmaceuticals gathered in distinct sites of the biofilm matrix. While citalopram penetrated the biofilm deeply, sertraline remained confined in its outer layer. Both pharmaceuticals seemed to mainly colocalize with phosphocholine lipids. Ketoconazole concentrated in small areas with high signal intensity. The approach outlined here presents a powerful strategy for visualizing the chemical composition of biofilms for wastewater treatment and demonstrates its promising utility for elucidating the mechanisms behind pharmaceutical and antimicrobial removal in biological wastewater treatment.

Increasing oxytetracycline and enrofloxacin concentrations on the algal growth and sewage purification performance of an algal-bacterial consortia system

Oxytetracycline (OTC) and enrofloxacin (EFX) pollution in surface water are very common. Using the algal-bacterial consortia system to remove antibiotics remains to be further studied. In this study, the algal growth and sewage purification performance were studied in an algal-bacterial consortia system with different concentrations of antibiotics. The enzyme activity, malondialdehyde content, chlorophyll-a content, extracellular polysaccharide, and protein content of algae were also tested. It was found that the algal growth was promoted by low-dose antibiotics, 21.83% and 22.11% promotion at 0.1 mg L^-1 OTC and EFX, respectively. The nutrients and antibiotics removals of the low-dose groups (OTC <5 mg L^-1, EFX <1 mg L^-1) were not affected significantly. More than 70% of total organic carbon and total phosphorus, and 97.84-99.76% OTC, 42.68-42.90% EFX were removed in the low-dose groups. However, the algal growth was inhibited, and the nutrients removals performance also declined in the high-concentration groups (10 mg L^-1 OTC, 5 mg L^-1 EFX). The superoxide dismutase and catalase activity, and malondialdehyde content increased significantly (P < 0.05), indicating the increased activity of reactive oxygen species. In addition, the decreased chlorophyll-a content, thylakoid membrane deformation, starch granules accumulation, and plasmolysis showed that the algal physiological functions were affected. These results showed that the algal-bacterial consortia system was more suitable to treat low-concentration antibiotics and provided basic parameters for the consortia application.

Biofilm Producing Rhizobacteria With Multiple Plant Growth-Promoting Traits Promote Growth of Tomato Under Water-Deficit Stress

Plant growth-promoting rhizobacteria (PGPR) not only enhance plant growth but also control phytopathogens and mitigate abiotic stresses, including water-deficit stress. In this study, 21 (26.9%) rhizobacterial strains isolated from drought-prone ecosystems of Bangladesh were able to form air–liquid (AL) biofilms in the glass test tubes containing salt-optimized broth plus glycerol (SOBG) medium. Based on 16S rRNA gene sequencing, Pseudomonas chlororaphis (ESR3 and ESR15), P. azotoformans ESR4, P. poae ESR6, P. fluorescens (ESR7 and ESR25), P. gessardii ESR9, P. cedrina (ESR12, ESR16, and ESR23), P. veronii (ESR13 and ESR21), P. parafulva ESB18, Stenotrophomonas maltophilia ESR20, Bacillus cereus (ESD3, ESD21, and ESB22), B. horikoshii ESD16, B. aryabhattai ESB6, B. megaterium ESB9, and Staphylococcus saprophyticus ESD8 were identified. Fourier transform infrared spectroscopy studies showed that the biofilm matrices contain proteins, polysaccharides, nucleic acids, and lipids. Congo red binding results indicated that these bacteria produced curli fimbriae and nanocellulose-rich polysaccharides. Expression of nanocellulose was also confirmed by Calcofluor binding assays and scanning electron microscopy. In vitro studies revealed that all these rhizobacterial strains expressed multiple plant growth-promoting traits including N₂ fixation, production of indole-3-acetic acid, solubilization of nutrients (P, K, and Zn), and production of ammonia, siderophores, ACC deaminase, catalases, lipases, cellulases, and proteases. Several bacteria were also tolerant to multifarious stresses such as drought, high temperature, extreme pH, and salinity. Among these rhizobacteria, P. cedrina ESR12, P. chlororaphis ESR15, and B. cereus ESD3 impeded the growth of Xanthomonas campestris pv. campestris ATCC 33913, while P. chlororaphis ESR15 and B. cereus ESD21 prevented the progression of Ralstonia solanacearum ATCC^® 11696^TM. In a pot experiment, tomato plants inoculated with P. azotoformans ESR4, P. poae ESR6, P. gessardii ESR9, P. cedrina ESR12, P. chlororaphis ESR15, S. maltophilia ESR20, P. veronii ESR21, and B. aryabhattai ESB6 exhibited an increased plant growth compared to the non-inoculated plants under water deficit-stressed conditions. Accordingly, the bacterial-treated plants showed a higher antioxidant defense system and a fewer tissue damages than non-inoculated plants under water-limiting conditions. Therefore, biofilm-producing PGPR can be utilized as plant growth promoters, suppressors of plant pathogens, and alleviators of water-deficit stress.

1,4-Naphthoquinone accumulates reactive oxygen species in Staphylococcus aureus: a promising approach towards effective management of biofilm threat

Staphylococcus aureus, a Gram-positive opportunistic microorganism, promotes pathogenicity in the human host through biofilm formation. Microorganisms associated with biofilm often exhibit drug-resistance property that poses a major threat to public healthcare. Thus, the exploration of new therapeutic approaches is the need of the hour to manage biofilm-borne infections. In the present study, efforts are put together to test the antimicrobial as well as antibiofilm activity of 1,4-naphthoquinone against Staphylococcus aureus. The result showed that the minimum bactericidal concentration (MBC) of this compound was found to be 100 µg/mL against Staphylococcus aureus. In this regard, an array of experiments (crystal violet, biofilm protein measurement, and microscopic analysis) related to biofilm assay were conducted with the sub-MBC concentrations (1/20 and 1/10 MBC) of 1,4-naphthoquinone. All the results of biofilm assay demonstrated that these tested concentrations (1/20 and 1/10 MBC) of the compound (1,4-naphthoquinone) showed a significant reduction in biofilm development by Staphylococcus aureus. Moreover, the tested concentrations (1/20 and 1/10 MBC) of the compound (1,4-naphthoquinone) were able to reduce the microbial motility of Staphylococcus aureus that might affect the development of biofilm. Further studies revealed that the treatment of 1,4-naphthoquinone to the organism was found to increase the cellular accumulation of reactive oxygen species (ROS) that resulted in the inhibition of biofilm formation by Staphylococcus aureus. Hence, it can be concluded that 1,4-naphthoquinone might be considered as a promising compound towards biofilm inhibition caused by Staphylococcus aureus.

Non-Destructive Monitoring of P. fluorescens and S. epidermidis Biofilm under Different Media by Fourier Transform Infrared Spectroscopy and Other Corroborative Techniques

In the present study, the early stage of bacteria biofilm formation has been studied as a function of different nutrients. Infrared spectra of Pseudomonas fluorescens (PF) and Staphylococcus epidermidis (SE), on germanium ATR crystal, were collected under deionized water H2O, phosphate buffered solution (PBS) and PBS with glucose (PBS-G). In H2O, protein bands of PF increased while, no difference in PBS and PBS-G were observed until 135 min. SE strain showed a low sensitivity to PBS composition starting to expose proteins on surfaces after 120 min. SE shows a low polysaccharides increase in H2O while, in bare and enriched PBS their intensity increases after 120 and 75 min. in PBS and PBS-G respectively. PF exhibits a peculiar behavior in H2O where the saccharide bands increased strongly after 100 min, while under all the other conditions, the intensity of polysaccharide bands increased up to the plateau probably because the layer of the biofilm exceeded the penetration capability of FTIR technique. All data suggest that, under lack of nutrients, both the bacteria tend to firmly anchor themselves to the support using proteins.

Biofilm formation and extracellular microvesicles-The way of foodborne pathogens toward resistance

Almost all known foodborne pathogens are able to form biofilms as one of the strategies for survival under harsh living conditions, to ward off the inhibition and the disinfection during food production, transport and storage, as well as during cleaning and sanitation of corresponding facilities. Biofilms are communities where microbial cells live under constant intracellular interaction and communication. Members of the biofilm community are embedded into extracellular matrix that contains polysaccharides, DNA, lipids, proteins, and small molecules that protect microorganisms and enable their intercellular communication under stress conditions. Membrane vesicles (MVs) are produced by both Gram positive and Gram negative bacteria. These lipid membrane-enveloped nanoparticles play an important role in biofilm genesis and in communication between different biofilm members. Furthermore, MVs are involved in other important steps of bacterial life like cell wall modeling, cellular division, and intercellular communication. They also carry toxins and virulence factors, as well as nucleic acids and different metabolites, and play a key role in host infections. After entering host cells, MVs can start many pathologic processes and cause serious harm and cell death. Prevention and inhibition of both biofilm formation and shedding of MVs by foodborne pathogens has a very important role in food production, storage, and food safety in general. Better knowledge of biofilm formation and maintaining, as well as the role of microbial vesicles in this process and in the process of host cells' infection is essential for food safety and prevention of both food spoilage and host infection.

Characterization of the biofilm grown on 304L stainless steel in urban wastewaters: extracellular polymeric substances (EPS) and bacterial consortia

Characterization of the biofilm growing on stainless steel (SS) in untreated (UTUWW) and treated (TUWW) urban wastewaters was performed. In both media, the first phase of biofilm growth was aerobic, when the genera Caldimonas, Caulobacter, Terriglobus and Edaphobacter (iron oxidizing bacteria [IOB]) and the genera Bacillus, Sulfurimonas, Syntrophobacter and Desulfobacter (sulfur oxidizing bacteria [SOB]) were identified. In the second phase, established after immersion for 7 days, the high amount of EPS inhibited the access of oxygen and promoted the growth of anaerobic bacteria, which were the genus Shewanella (iron-reducing bacterium [IRB]) and the genera Desulfovirga, Desulfovibrio, Desulfuromusa, Desulfococcus, and Desulfosarcina (sulfate-reducing bacteria [SRB]). Electrochemical measurements showed that in the first stage, the aerobic bacteria and the high amount of EPS delayed the cathodic reduction of oxygen. However, in the second stage, EPS and the anaerobic bacteria promoted anodic dissolution.

Analysis of Pseudomonas aeruginosa biofilm membrane vesicles supports multiple mechanisms of biogenesis

Outer Membrane Vesicles (OMVs) are ubiquitous in bacterial environments and enable interactions within and between species. OMVs are observed in lab-grown and environmental biofilms, but our understanding of their function comes primarily from planktonic studies. Planktonic OMVs assist in toxin delivery, cell-cell communication, horizontal gene transfer, small RNA trafficking, and immune system evasion. Previous studies reported differences in size and proteomic cargo between planktonic and agar plate biofilm OMVs, suggesting possible differences in function between OMV types. In Pseudomonas aeruginosa interstitial biofilms, extracellular vesicles were reported to arise through cell lysis, in contrast to planktonic OMV biogenesis that involves the Pseudomonas Quinolone Signal (PQS) without appreciable autolysis. Differences in biogenesis mechanism could provide a rationale for observed differences in OMV characteristics between systems. Using nanoparticle tracking, we found that P. aeruginosa PAO1 planktonic and biofilm OMVs had similar characteristics. However, P. aeruginosa PA14 OMVs were smaller, with planktonic OMVs also being smaller than their biofilm counterparts. Large differences in Staphylococcus killing ability were measured between OMVs from different strains, and a smaller within-strain difference was recorded between PA14 planktonic and biofilm OMVs. Across all conditions, the predatory ability of OMVs negatively correlated with their size. To address biogenesis mechanism, we analyzed vesicles from wild type and pqsA mutant biofilms. This showed that PQS is required for physiological-scale production of biofilm OMVs, and time-course analysis confirmed that PQS production precedes OMV production as it does in planktonic cultures. However, a small sub-population of vesicles was detected in pqsA mutant biofilms whose size distribution more resembled sonicated cell debris than wild type OMVs. These results support the idea that, while a small and unique population of vesicles in P. aeruginosa biofilms may result from cell lysis, the PQS-induced mechanism is required to generate the majority of OMVs produced by wild type communities.

An extraction free modified o-phthalaldehyde assay for quantifying residual protein and microbial biofilms on surfaces

Biological contamination of surfaces in industry and healthcare is an important vector of disease transmission. Current assays for detecting surface-adherent contamination require extraction of biological soil. However, physical inaccessibility or poor solubility may limit recovery. Here, how the o-phthalaldehyde (OPA) protein assay can be modified to measure residual protein (modeled with bovine serum albumin) or biofilm on a surface without extraction is described. The assay limit of detection (LOD) for protein was 1.6 µg cm^-2. The detection threshold for Staphylococcus epidermis biofilm was 117 µg cm^-2. The clinical utility of the method was demonstrated for measurements taken from clinically used endoscopes. Since this method is more sensitive than extraction-based testing, clinical results should not be compared with conventional benchmarks. By enabling direct detection and quantification of soils in complex or hard-to-reach areas, this method has potential to improve the margin of safety in medical and industrial cleaning processes.

Metal-Adapted Bacteria Isolated From Wastewaters Produce Biofilms by Expressing Proteinaceous Curli Fimbriae and Cellulose Nanofibers

Bacterial biofilm plays a pivotal role in bioremediation of heavy metals from wastewaters. In this study, we isolated and identified different biofilm producing bacteria from wastewaters. We also characterized the biofilm matrix [i.e., extracellular polymeric substances (EPS)] produced by different bacteria. Out of 40 isolates from different wastewaters, only 11 (27.5%) isolates (static condition at 28°C) and 9 (22.5%) isolates (agitate and static conditions at 28 and 37°C) produced air–liquid (AL) and solid–air–liquid (SAL) biofilms, respectively, only on salt-optimized broth plus 2% glycerol (SOBG) but not in other media tested. Biomass biofilms and bacteria coupled with AL biofilms were significantly (P ≤ 0.001) varied in these isolates. Escherichia coli (isolate ENSD101 and ENST501), Enterobacter asburiae (ENSD102), Enterobacter ludwigii (ENSH201), Pseudomonas fluorescens (ENSH202 and ENSG304), uncultured Vitreoscilla sp. (ENSG301 and ENSG305), Acinetobacter lwoffii (ENSG302), Klebsiella pneumoniae (ENSG303), and Bacillus thuringiensis (ENSW401) were identified based on 16S rRNA gene sequencing. Scanning electron microscope (SEM) images revealed that biofilm matrix produced by E. asburiae ENSD102, uncultured Vitreoscilla sp. ENSG301, A. lwoffii ENSG302, and K. pneumoniae ENSG303 are highly fibrous, compact, and nicely interlinked as compared to the biofilm developed by E. ludwigii ENSH201 and B. thuringiensis ENSW401. X-ray diffraction (XRD) results indicated that biofilm matrix produced by E. asburiae ENSD102, uncultured Vitreoscilla sp. ENSG301, and A. lwoffii ENSG302 are non-crystalline amorphous nature. Fourier transform infrared (FTIR) spectroscopy showed that proteins and polysaccharides are the main components of the biofilms. Congo red binding results suggested that all these bacteria produced proteinaceous curli fimbriae and cellulose-rich polysaccharide. Production of cellulose was also confirmed by Calcofluor binding- and spectrophotometric assays. E. asburiae ENSD102, Vitreoscilla sp. ENSG301, and A. lwoffii ENSG302 were tested for their abilities to form the biofilms exposure to 0 to 2000 mg/L of copper sulfate (for Cu), zinc sulfate (for Zn), lead nitrate (for Pb), nickel chloride (for Ni), and potassium dichromate (for Cr), several concentrations of these metals activated the biofilm formation. The polysaccharides is known to sequester the heavy metals thus, these bacteria might be applied to remove the heavy metals from wastewater.

Atomic force microscopy studies of bioprocess engineering surfaces - imaging, interactions and mechanical properties mediating bacterial adhesion

The detrimental effect of bacterial biofilms on process engineering surfaces is well documented. Thus, interest in the early stages of bacterial biofilm formation; in particular bacterial adhesion and the production of anti-fouling coatings has grown exponentially as a field. During this time, Atomic force microscopy (AFM) has emerged as a critical tool for the evaluation of bacterial adhesion. Due to its versatility AFM offers not only insight into the topographical landscape and mechanical properties of the engineering surfaces, but elucidates, through direct quantification the topographical and biomechnical properties of the foulants The aim of this review is to collate the current research on bacterial adhesion, both theoretical and practical, and outline how AFM as a technique is uniquely equipped to provide further insight into the nanoscale world at the bioprocess engineering surface.

Interfacial photochemistry of biogenic surfactants: a major source of abiotic volatile organic compounds

Films of biogenic compounds exposed to the atmosphere are ubiquitously found on the surfaces of cloud droplets, aerosol particles, buildings, plants, soils and the ocean. These air/water interfaces host countless amphiphilic compounds concentrated there with respect to in bulk water, leading to a unique chemical environment. Here, photochemical processes at the air/water interface of biofilm-containing solutions were studied, demonstrating abiotic VOC production from authentic biogenic surfactants under ambient conditions. Using a combination of online-APCI-HRMS and PTR-ToF-MS, unsaturated and functionalized VOCs were identified and quantified, giving emission fluxes comparable to previous field and laboratory observations. Interestingly, VOC fluxes increased with the decay of microbial cells in the samples, indicating that cell lysis due to cell death was the main source for surfactants and VOC production. In particular, irradiation of samples containing solely biofilm cells without matrix components exhibited the strongest VOC production upon irradiation. In agreement with previous studies, LC-MS measurements of the liquid phase suggested the presence of fatty acids and known photosensitizers, possibly inducing the observed VOC productionviaperoxy radical chemistry. Up to now, such VOC emissions were directly accounted to high biological activity in surface waters. However, the results obtained suggest that abiotic photochemistry can lead to similar emissions into the atmosphere, especially in less biologically-active regions. Furthermore, chamber experiments suggest that oxidation (O₃/OH radicals) of the photochemically-produced VOCs leads to aerosol formation and growth, possibly affecting atmospheric chemistry and climate-related processes, such as cloud formation or the Earth’s radiation budget.

Synergistic effect using vermiculite as media with a bacterial biofilm of Arthrobacter sp. for biodegradation of di-(2-ethylhexyl) phthalate

Vermiculite is one of matrix material used for constructed wetland (CW) for the treatment of municipal wastewater. Arthrobacter sp. strain C21 (CGMCC No. 7671), isolated from a constructed wetland receiving municipal wastewater, forms biofilm on the surface of vermiculite. Di-(2-ethylhexyl) phthalate (DEHP), a typical phthalate pollutant in environment, can be degraded by the biofilm of strain C21 formed on vermiculite. Results of laboratory studies indicated that DEHP was removed from aqueous phase via biodegradation, adsorption by vermiculite, and adsorption by biofilm biomass. Synergistic effect of these three reactions enhanced the overall DEHP removal efficiency. During a batch incubation test with vermiculite and the cell suspension, bacterial adhesion to the media surface occurred within 5h and the phthalate esters (PEs) removal was due to both biodegradation and vermiculite adsorption. As the biofilm developed on surface of vermiculite (5-36 h), biodegradation became the predominance for PEs removal. As mature biofilm was formed (36-54 h), the adsorption of PEs by biofilm biomass became a main driving force for the removal of PEs from aqueous phase. The content of extracellular polymers (EPS) of the biofilm and DEHP removal performance showed a significant positive correlation (rp>0.86).

Proteins dominate in the surface layers formed on materials exposed to extracellular polymeric substances from bacterial cultures

The chemical compositions of the surface conditioning layers formed by different types of solutions (from isolated EPS to whole culture media), involving different bacterial strains relevant for biocorrosion were compared, as they may influence the initial step in biofilm formation. Different substrata (polystyrene, glass, steel) were conditioned and analyzed by X-ray photoelectron spectroscopy. Peak decomposition and assignment were validated by correlations between independent spectral data and the ubiquitous presence of organic contaminants on inorganic substrata was taken into account. Proteins or peptides were found to be a major constituent of all conditioning layers and polysaccharides were not present in appreciable concentrations; the proportion of nitrogen which may be due to DNA was lower than 15%. There was no significant difference between the compositions of the adlayers formed from different conditioning solutions, except for the adlayers produced with tightly bound EPS extracted from D. alaskensis.

Rhodococcus erythropolis cells adapt their fatty acid composition during biofilm formation on metallic and non-metallic surfaces

Several parameters are involved in bacterial adhesion and biofilm formation including surface type, medium composition and cellular surface hydrophobicty. When the cells are placed inside tubes, parameters such as oxygen availability should also influence cell adhesion. To understand which cellular lipids are involved in the molecular events of biofilm formation in Rhodococcus erythropolis, cell adhesion was promoted on different metallic and non-metallic surfaces immersed in culture media. These cells were able to modulate the fatty acid composition of the cell membrane in response to both the surface to which they adhered and the growth medium used. To assess the response of the cells to both surfaces and operational conditions, biofilms were also promoted inside a reactor built with five different types of tubes and with medium recirculation. The biofilm biomass could be directly related not to the hydrophobicity of the tubes used but to the oxygen permeability of the tubes. Besides this, cell age influenced the adhesion of the R. erythropolis cells to the tubes. Principal component analysis showed that the lipid composition of the cells could separate cells attached to metallic from those on non-metallic surfaces in the plane formed by PC1 and PC2, and influence biofilm biomass.

The role of bacterial biofilms and surface components in plant-bacterial associations

The role of bacterial surface components in combination with bacterial functional signals in the process of biofilm formation has been increasingly studied in recent years. Plants support a diverse array of bacteria on or in their roots, transport vessels, stems, and leaves. These plant-associated bacteria have important effects on plant health and productivity. Biofilm formation on plants is associated with symbiotic and pathogenic responses, but how plants regulate such associations is unclear. Certain bacteria in biofilm matrices have been found to induce plant growth and to protect plants from phytopathogens (a process termed biocontrol), whereas others are involved in pathogenesis. In this review, we systematically describe the various components and mechanisms involved in bacterial biofilm formation and attachment to plant surfaces and the relationships of these mechanisms to bacterial activity and survival.

Staphylococcus epidermidis with the icaA⁻/icaD⁻/IS256⁻ genotype and protein or protein/extracellular-DNA biofilm is frequent in ocular infections

In ocular infections (OIs) caused by Staphylococcus epidermidis, biofilms composed mainly of poly-N-acetylglucosamine (PNAG) have been widely studied, but PNAG-independent biofilms have not. Therefore, we searched for a relationship between the ica operon (involved in PNAG-biofilm) and the biochemical composition of biofilms in isolates from OI. Isolates from OI (n = 62), from healthy conjunctiva (HC; n = 45) and from healthy skin (HS; n = 53), were used to detect icaA and icaD genes, and the insertion sequence 256 (IS256) using PCR. The compositions of the biofilms were determined by treatment with NaIO₄, proteinase K and DNase I. Multilocus sequence typing (MLST) was performed to characterize the isolates, and the expression of aap and embp genes was determined by real-time qPCR. A strong relationship between the icaA(-)/icaD(-)/IS256(-) genotype and protein- or protein/extracellular DNA (eDNA)-biofilm composition was found in the isolates from OI (53.6%), whereas the icaA(+)/icaD(+)/IS256(-) genotype and carbohydrate-biofilm was most prevalent in isolates from HC (25%) and HS (25%). Isolates with an icaA(-)/icaD(-)/IS256(-) genotype and protein-biofilm phenotype were predominantly of the ST2 lineage, while carbohydrate-biofilm-producing strains were mainly of the ST9 lineage. The protein-biofilm-producing strains had higher expression levels of aap gene than carbohydrate-biofilm-producing strains; while embp gene did not have the same pattern of expression. These results suggest that S. epidermidis strains with icaA(-)/icaD(-)/IS256(-) genotype and protein- or protein/eDNA-biofilms have a stronger ability to establish in the eye than S. epidermidis strains with icaA(+)/icaD(+)/IS256(-) genotype and PNAG-biofilms.

Bacterial biofilms: development, dispersal, and therapeutic strategies in the dawn of the postantibiotic era

Biofilm formation constitutes an alternative lifestyle in which microorganisms adopt a multicellular behavior that facilitates and/or prolongs survival in diverse environmental niches. Biofilms form on biotic and abiotic surfaces both in the environment and in the healthcare setting. In hospital wards, the formation of biofilms on vents and medical equipment enables pathogens to persist as reservoirs that can readily spread to patients. Inside the host, biofilms allow pathogens to subvert innate immune defenses and are thus associated with long-term persistence. Here we provide a general review of the steps leading to biofilm formation on surfaces and within eukaryotic cells, highlighting several medically important pathogens, and discuss recent advances on novel strategies aimed at biofilm prevention and/or dissolution.

Spo0A links de novo fatty acid synthesis to sporulation and biofilm development in Bacillus subtilis

During sporulation in Bacillus subtilis, the committed-cell undergoes substantial membrane rearrangements to generate two cells of different sizes and fates: the mother cell and the forespore. Here, we demonstrate that the master transcription factor Spo0A reactivates lipid synthesis during development. Maximal Spo0A-dependent lipid synthesis occurs during the key stages of asymmetric division and forespore engulfment. Spo0A reactivates the accDA operon that encodes the carboxylase component of the acetyl-CoA carboxylase enzyme, which catalyses the first and rate-limiting step in de novo lipid biosynthesis, malonyl-CoA formation. The disruption of the Spo0A-binding box in the promoter region of accDA impairs its transcriptional reactivation and blocks lipid synthesis. The Spo0A-insensitive accDA(0A) cells were proficient in planktonic growth but defective in sporulation (σ(E) activation) and biofilm development (cell cluster formation and water repellency). Exogenous fatty acid supplementation to accDA(0A) cells overcomes their inability to synthesize lipids during development and restores sporulation and biofilm proficiencies. The transient exclusion of the lipid synthesis regulon from the forespore and the known compartmentalization of Spo0A and ACP in the mother cell suggest that de novo lipid synthesis is confined to the mother cell. The significance of the Spo0A-controlled de novo lipid synthesis during B. subtilis development is discussed.

Occurrence and composition of extracellular lipids and polysaccharides in a full-scale membrane bioreactor

The aim of this study was to characterize the polysaccharides and lipid fractions of membrane foulants in a full-scale membrane bioreactor (MBR) treating municipal wastewater. Both of these polymeric compounds are major components of bacterial lipopolysaccharides and are impacting membrane fouling; however most of the data so far have been collected by determining sum parameters rather than the detailed composition of these polymers. Photometric analysis of sugars showed that uronic acids (glucuronic, mannuronic and galacturonic acid) as common units of bacterial polysaccharides accounted for 8% (w/w) of extracellular polymeric substances (EPS) in activated sludge flocs. Further the so-called polysaccharide peak of EPS, with a molecular weight >10 kDa according to size exclusion chromatography, was proven to contain bacterial sugar units as shown by high resolution LC-MS. Interestingly, only traces of uronic acids could be detected in EPS of the membrane fouling layer. A far more dramatic enrichment in the fouling layer was revealed for the lipid fraction of EPS, which was determined as fatty acid methyl esters by GC-MS. The weight percentage of fatty acids in EPS extracted from fouled ultrafiltration membranes was much higher (10%) than in the activated sludge itself (1-3%). The fatty acids accumulated on the membrane fouling layer were obviously not only of microbial origin (C16:0, C18:0) but also derived from the raw wastewater itself (C9:0). Hydrophobic interaction of lipids with the PVDF (polyvinylidene fluoride) membrane material therefore seems a plausible explanation for the observed fouling phenomenon. The results suggest that fatty acids from bacterial lipopolysaccharides as well as from synthetic sources are of much higher relevance to membrane fouling than previously assumed.

Selected ion monitoring in quantitative gas–liquid chromatographic – mass spectrometric detection of fatty acid methyl esters from environmental samples

To calculate selected ion monitoring (SIM) gas-liquid chromatography (GLC)-mass spectrometry (MS) results of phospholipid fatty acids (PLFAs) from environmental samples, coefficients were calculated for each fatty acid by dividing the sum of ion intensities in SCAN with that of ions followed in SIM. The SIM chromatogram areas were multiplied with the coefficients, and then processed as in SCAN. The results were compared to those obtained using calibration curves and SCAN. The calibration curve and coefficient based results had the greatest errors of 7.8 and 6.7%, respectively, outside standard deviations of SCAN percentages. The PLFA contents calculated using calibration curves and coefficients were 104.9+/-7.3% and 101.5+/-8.6%, respectively, of SCAN values. SIM increased sensitivity approximately 10-fold from SCAN, and the smallest detectable injected amount was approximately 50 ng (0.18 nmol) for 20 fatty acids, corresponding to 4 x 10(6) cells.