The biofilm matrix: multitasking in a shared space

The biofilm matrix can be considered to be a shared space for the encased microbial cells, comprising a wide variety of extracellular polymeric substances (EPS), such as polysaccharides, proteins, amyloids, lipids and extracellular DNA (eDNA), as well as membrane vesicles and humic-like microbially derived refractory substances. EPS are dynamic in space and time and their components interact in complex ways, fulfilling various functions: to stabilize the matrix, acquire nutrients, retain and protect eDNA or exoenzymes, or offer sorption sites for ions and hydrophobic substances. The retention of exoenzymes effectively renders the biofilm matrix an external digestion system influencing the global turnover of biopolymers, considering the ubiquitous relevance of biofilms. Physico-chemical and biological interactions and environmental conditions enable biofilm systems to morph into films, microcolonies and macrocolonies, films, ridges, ripples, columns, pellicles, bubbles, mushrooms and suspended aggregates - in response to the very diverse conditions confronting a particular biofilm community. Assembly and dynamics of the matrix are mostly coordinated by secondary messengers, signalling molecules or small RNAs, in both medically relevant and environmental biofilms. Fully deciphering how bacteria provide structure to the matrix, and thus facilitate and benefit from extracellular reactions, remains the challenge for future biofilm research.

Exopolysaccharide composition and size in Sulfolobus acidocaldarius biofilms

Extracellular polymeric substances (EPS) comprise mainly carbohydrates, proteins and extracellular DNA (eDNA) in biofilms formed by the thermoacidophilic Crenarchaeon Sulfolobus acidocaldarius. However, detailed information on the carbohydrates in the S. acidocaldarius biofilm EPS, i.e., the exopolysaccharides (PS), in terms of identity, composition and size were missing. In this study, a set of methods was developed and applied to study the PS in S. acidocaldarius biofilms. It was initially shown that addition of sugars, most significantly of glucose, to the basal N-Z-amine-based growth medium enhanced biofilm formation. For the generation of sufficient amounts of biomass suitable for chemical analyses, biofilm growth was established and optimized on the surface of membrane filters. EPS were isolated and the contents of carbohydrates, proteins and eDNA were determined. PS purification was achieved by enzymatic digestion of other EPS components (nucleic acids and proteins). After trifluoroacetic acid-mediated hydrolysis of the PS fraction, the monosaccharide composition was analyzed by reversed-phase liquid chromatography (RP-LC) coupled to mass spectrometry (MS). Main sugar constituents detected were mannose, glucose and ribose, as well as minor proportions of rhamnose, N-acetylglucosamine, glucosamine and galactosamine. Size exclusion chromatography (SEC) revealed the presence of one single PS fraction with a molecular mass of 4-9 × 10⁴ Da. This study provides detailed information on the PS composition and size of S. acidocaldarius MW001 biofilms and methodological tools for future studies on PS biosynthesis and secretion.

Characterization of the Extracellular Volatile Metabolome of Pseudomonas Aeruginosa Applying an in vitro Biofilm Model under Cystic Fibrosis-Like Conditions

BACKGROUND

Cystic fibrosis (CF) is an autosomal recessive hereditary disease that leads to the production of thickened mucus in the lungs, favouring polymicrobial infections, such as chronic lung infections with the bacterial opportunistic pathogen Pseudomonas aeruginosa.

METHOD

A biofilm model in combination with an adapted sampling and GC-MS analysis method were applied to in vitro studies on different variables influencing the composition of the extracellular volatile metabolome of P. aeruginosa.

RESULTS

A significant influence on the metabolome could be demonstrated for the culture medium as well as the atmosphere during cultivation (aerobic or anaerobic). Furthermore, a significant influence of the mucoid (alginate-overproducing) phenotype of the bacterium on quantity and composition of volatile organic compounds could be observed. Based on the results a solid culture medium was developed to simulate the nutrient conditions in the lungs of a CF patient. The extracellular volatile metabolome of bacterial strains P. aeruginosa ATCC 10145, PAO1 and FRD1 was characterized under CF-like conditions.

CONCLUSIONS

Bacterial strain-dependent metabolites were identified. When P. aeruginosa PAO1 and FRD1 clinical isolates were compared, 36 metabolites showed significant variations in intensities. When the clinical isolates were compared with the reference strain (P. aeruginosa ATCC 10145), 28 metabolites (P. aeruginosa PAO1) and 70 metabolites (P. aeruginosa FRD1) were determined whose peaks showed significant deviation (p > 95%) in intensity. Furthermore, the bacterial strains could be differentiated from each other by means of two principal components.

Thermal and chemical disinfection of water and biofilms: only a temporary effect in regard to the autochthonous bacteria

Thermal and chemical disinfection of technical water systems not only aim at minimizing the level of undesired microorganisms, but also at preventing excessive biofouling, clogging and interference with diverse technical processes. Typically, treatment has to be repeated in certain time intervals, as the duration of the effect is limited. The transient effect of disinfection was demonstrated in this study applying different treatments to water and biofilms including heat, chlorination, a combination of hydrogen peroxide and peracetic acid and monochloramine. Despite the diverse treatments, the reduction in live bacteria was followed by regrowth in all cases, underlining the universal validity of this phenomenon. The study shows that autochthonous bacteria can reach the concentrations given prior to treatment. The reason is seen in the nutrient concentration that has not changed and that forms the basis for regrowth. Nutrients are released by disinfection from lysed cells or are still fixed in dead biomass that is subsequently scavenged by necrotrophic growth. Treatment cycles therefore only provide a transient reduction of water microbiology if nutrients are not removed. When aiming at greater sustainability of the effect, biocidal treatment has to be equally concerned about nutrient removal by subsequent cleaning procedures as about killing efficiency.

Who put the film in biofilm? The migration of a term from wastewater engineering to medicine and beyond

Sessile microorganisms were described as early as the seventeenth century. However, the term biofilm arose only in the 1960s in wastewater treatment research and was adopted later in marine fouling and in medical and dental microbiology. The sessile mode of microbial life was gradually recognized to be predominant on Earth, and the term biofilm became established for the growth of microorganisms in aggregates, frequently associated with interfaces, although many, if not the majority, of them not being continuous "films" in the strict sense. In this sessile form of life, microorganisms live in close proximity in a matrix of extracellular polymeric substances (EPS). They share emerging properties, clearly distinct from solitary free floating planktonic microbial cells. Common characteristics include the formation of synergistic microconsortia, using the EPS matrix as an external digestion system, the formation of gradients and high biodiversity over microscopically small distances, resource capture and retention, facilitated gene exchange as well as intercellular communication, and enhanced tolerance to antimicrobials. Thus, biofilms belong to the class of collective systems in biology, like forests, beehives, or coral reefs, although the term film addresses only one form of the various manifestations of microbial aggregates. The uncertainty of this term is discussed, and it is acknowledged that it will not likely be replaced soon, but it is recommended to understand these communities in the broader sense of microbial aggregates.

Tolerances of Deinococcus geothermalis Biofilms and Planktonic Cells Exposed to Space and Simulated Martian Conditions in Low Earth Orbit for Almost Two Years

Fossilized biofilms represent one of the oldest known confirmations of life on the Earth. The success of microbes in biofilms results from properties that are inherent in the biofilm, including enhanced interaction, protection, and biodiversity. Given the diversity of microbes that live in biofilms in harsh environments on the Earth, it is logical to hypothesize that, if microbes inhabit other bodies in the Universe, there are also biofilms on those bodies. The Biofilm Organisms Surfing Space experiment was conducted as part of the EXPOSE-R2 mission on the International Space Station. The experiment was an international collaboration designed to perform a comparative study regarding the survival of biofilms versus planktonic cells of various microorganisms, exposed to space and Mars-like conditions. The objective was to determine whether there are lifestyle-dependent differences to cope with the unique mixture of stress factors, including desiccation, temperature oscillations, vacuum, or a Mars-like gas atmosphere and pressure in combination with extraterrestrial or Mars-like ultraviolet (UV) radiation residing during the long-term space mission. In this study, the outcome of the flight and mission ground reference analysis of Deinococcus geothermalis is presented. Cultural tests demonstrated that D. geothermalis remained viable in the desiccated state, being able to survive space and Mars-like conditions and tolerating high extraterrestrial UV radiation for more than 2 years. Culturability decreased, but was better preserved, in the biofilm consortium than in planktonic cells. These results are correlated to differences in genomic integrity after exposure, as visualized by random amplified polymorphic DNA-polymerase chain reaction. Interestingly, cultivation-independent viability markers such as membrane integrity, ATP content, and intracellular esterase activity remained nearly unaffected, indicating that subpopulations of the cells had survived in a viable but nonculturable state. These findings support the hypothesis of long-term survival of microorganisms under the harsh environmental conditions in space and on Mars to a higher degree if exposed as biofilm.

Distribution of Escherichia coli, coliphages and enteric viruses in water, epilithic biofilms and sediments of an urban river in Germany

Fecal contamination of surface water is commonly evaluated by quantification of bacterial or viral indicators such as Escherichia coli and coliphages, or by direct testing for pathogens such as enteric viruses. Retention of fecally derived organisms in biofilms and sediments is less frequently considered. In this study, we assessed the distribution of E. coli, somatic coliphages, and enteric viruses including human adenovirus (HAdV), enterovirus (EV), norovirus genogroup GII (NoV GII) and group A rotavirus (RoV) in an urban river environment in Germany. 24 samples each of water, epilithic biofilms and sediments were examined. E. coli and somatic coliphages were prevalent not only in the flowing water, but also in epilithic biofilms and sediments, where they were accumulated compared to the overlying water. During enhanced rainfall, E. coli and coliphage concentrations increased by approximately 2.5 and 1 log unit, respectively, in the flowing water, whereas concentrations did not change significantly in epilithic biofilms and sediments. The occurrence of human enteric viruses detected by qPCR was higher in water than in biofilms and sediments. 87.5% of all water samples were positive for HAdV. Enteric viruses found less frequently were EV, RoV and NoV GII in 20.8%, 16.7% and 8.3% of the water samples, respectively. In epilithic biofilms and sediments, HAdV was found in 54.2% and 50.0% of the samples, respectively, and EV was found in 4.2% of both biofilm and sediment samples. RoV and NoV GII were not detected in any of the biofilms and sediments. Overall, the prevalence of enteric viruses was in the order of HAdV > EV > RoV ≥ NoV GII. In conclusion, epilithic biofilms and sediments can be reservoirs for fecal indicators and enteric viruses and thus should be taken into consideration when assessing microbial pollution of surface water environments.

Influence of the copper-induced viable but non-culturable state on the toxicity of Pseudomonas aeruginosa towards human bronchial epithelial cells in vitro

The viable but non-culturable (VBNC) state of the opportunistic bacterium Pseudomonas aeruginosa was previously shown to be induced by copper ions in concentrations relevant to those in drinking water plumbing systems. This decrease of bacterial culturability without loss of viability might have an influence on human health due to an underestimation of the actual contamination in drinking water systems. The aim of this study was to investigate the influence of culturable P. aeruginosa, viable but not culturable as well as culturable again after resuscitation from the VBNC state on human bronchial epithelial cells (BEAS-2B) in vitro. Cyto- and genotoxic effects of P. aeruginosa at different states were studied using trypan blue, MTT, xCELLigence as well as the micronucleus assay. While P. aeruginosa in the VBNC state did not have any cytotoxic or genotoxic effect on BEAS-2B cells, untreated (culturable) and resuscitated P. aeruginosa did show cell damage, including disruption of cell membranes, inhibition of mitochondrial activity and cell proliferation as well as DNA-damaging effects. We conclude from our study that P. aeruginosa after resuscitation from the VBNC state regains its viability and cyto-/genotoxicity and therefore might influence human health.

Biofilms: an emergent form of bacterial life

Bacterial biofilms are formed by communities that are embedded in a self-produced matrix of extracellular polymeric substances (EPS). Importantly, bacteria in biofilms exhibit a set of 'emergent properties' that differ substantially from free-living bacterial cells. In this Review, we consider the fundamental role of the biofilm matrix in establishing the emergent properties of biofilms, describing how the characteristic features of biofilms - such as social cooperation, resource capture and enhanced survival of exposure to antimicrobials - all rely on the structural and functional properties of the matrix. Finally, we highlight the value of an ecological perspective in the study of the emergent properties of biofilms, which enables an appreciation of the ecological success of biofilms as habitat formers and, more generally, as a bacterial lifestyle.

Survival of Deinococcus geothermalis in Biofilms under Desiccation and Simulated Space and Martian Conditions

Biofilm formation represents a successful survival strategy for bacteria. In biofilms, cells are embedded in a matrix of extracellular polymeric substances (EPS). As they are often more stress-tolerant than single cells, biofilm cells might survive the conditions present in space and on Mars. To investigate this topic, the bacterium Deinococcus geothermalis was chosen as a model organism due to its tolerance toward desiccation and radiation. Biofilms cultivated on membranes and, for comparison, planktonically grown cells deposited on membranes were air-dried and exposed to individual stressors that included prolonged desiccation, extreme temperatures, vacuum, simulated martian atmosphere, and UV irradiation, and they were exposed to combinations of stressors that simulate space (desiccation + vacuum + UV) or martian (desiccation + Mars atmosphere + UV) conditions. The effect of sulfatic Mars regolith simulant on cell viability during stress was investigated separately. The EPS produced by the biofilm cells contained mainly polysaccharides and proteins. To detect viable but nonculturable (VBNC) cells, cultivation-independent viability indicators (membrane integrity, ATP, 16S rRNA) were determined in addition to colony counts. Desiccation for 2 months resulted in a decrease of culturability with minor changes of membrane integrity in biofilm cells and major loss of membrane integrity in planktonic bacteria. Temperatures between -25°C and +60°C, vacuum, and Mars atmosphere affected neither culturability nor membrane integrity in both phenotypes. Monochromatic (254 nm; ≥1 kJ m^-2) and polychromatic (200-400 nm; >5.5 MJ m^-2 for planktonic cells and >270 MJ m^-2 for biofilms) UV irradiation significantly reduced the culturability of D. geothermalis but did not affect cultivation-independent viability markers, indicating the induction of a VBNC state in UV-irradiated cells. In conclusion, a substantial proportion of the D. geothermalis population remained viable under all stress conditions tested, and in most cases the biofilm form proved advantageous for surviving space and Mars-like conditions. Key Words: Biofilms-Desiccation-UV radiation-Mars-Lithopanspermia. Astrobiology 17, 431-447.

Evaluating the influence of wastewater composition on the growth of Microthrix parvicella by GCxGC/qMS and real-time PCR

This study underlines the significance of long chain fatty acid (LCFA) content in wastewater influents as an influencing factor promoting the growth of Candidatus 'Microthrix parvicella' (M. parvicella), the most common filamentous bacteria causing foam in activated sludge systems worldwide. Quantification of M. parvicella by real-time polymerase chain reaction (real-time PCR) and analysis of LCFAs by means of two-dimensional gas chromatography coupled with mass spectrometry (GCxGC/qMS), involving solid phase micro-extraction (SPME) to enhance sensitivity, were combined for the first time as a monitoring tool. The results indicate a highly significant correlation between the abundance of M. parvicella and the total LCFA loading (r = 0.96) and linolenic acid C18:3 (r = 0.98) in particular. Additionally, comparison of slope values for the direct correlations of all significant LCFAs found in the analyses showed that the influence of LCFAs on M. parvicella growth increases with an increasing degree of unsaturation of carbon chains. These findings suggest that by removing lipid compounds from the incoming waters, substrate availability would be limited for M. parvicella.

Reducing pathogens in combined sewer overflows using ozonation or UV irradiation

Fecal contamination of water resources is a major public health concern in densely populated areas since these water bodies are used for drinking water production or recreational purposes. A main source of this contamination originates from combined sewer overflows (CSOs) in regions with combined sewer systems. Thus, the treatment of CSO discharges is urgent. In this study, we explored whether ozonation or UV irradiation can efficiently reduce pathogenic bacteria, viruses, and protozoan parasites in CSOs. Experiments were carried out in parallel settings at the outflow of a stormwater settling tank in the Ruhr area, Germany. The results showed that both techniques reduce most hygienically relevant bacteria, parasites and viruses. Under the conditions tested, ozonation yielded lower outflow values for the majority of the tested parameters.

Isolation of Extracellular Polymeric Substances from Biofilms of the Thermoacidophilic Archaeon Sulfolobus acidocaldarius

Extracellular polymeric substances (EPS) are the major structural and functional components of microbial biofilms. The aim of this study was to establish a method for EPS isolation from biofilms of the thermoacidophilic archaeon, Sulfolobus acidocaldarius, as a basis for EPS analysis. Biofilms of S. acidocaldarius were cultivated on the surface of gellan gum-solidified Brock medium at 78°C for 4 days. Five EPS extraction methods were compared, including shaking of biofilm suspensions in phosphate buffer, cation-exchange resin (CER) extraction, and stirring with addition of EDTA, crown ether, or NaOH. With respect to EPS yield, impact on cell viability, and compatibility with subsequent biochemical analysis, the CER extraction method was found to be the best suited isolation procedure resulting in the detection of carbohydrates and proteins as the major constituents and DNA as a minor component of the EPS. Culturability of CER-treated cells was not impaired. Analysis of the extracellular proteome using two-dimensional gel electrophoresis resulted in the detection of several hundreds of protein spots, mainly with molecular masses of 25–116 kDa and pI values of 5–8. Identification of proteins suggested a cytoplasmic origin for many of these proteins, possibly released via membrane vesicles or biofilm-inherent cell lysis during biofilm maturation. Functional analysis of EPS proteins, using fluorogenic substrates as well as zymography, demonstrated the activity of diverse enzyme classes, such as proteases, lipases, esterases, phosphatases, and glucosidases. In conclusion, the CER extraction method, as previously applied to bacterial biofilms, also represents a suitable method for isolation of water soluble EPS from the archaeal biofilms of S. acidocaldarius, allowing the investigation of composition and function of EPS components in these types of biofilms.

Nanosilver induces a non-culturable but metabolically active state in Pseudomonas aeruginosa

The antimicrobial properties of silver nanoparticles (AgNPs) have raised expectations for the protection of medical devices and consumer products against biofilms. The effect of silver on bacteria is commonly determined by culture-dependent methods. It is as yet unknown if silver-exposed bacteria can enter a metabolically active but non-culturable state. In this study, the efficacy of chemically synthesized AgNPs and silver as silver nitrate (AgNO3) against planktonic cells and biofilms of Pseudomonas aeruginosa AdS was investigated in microtiter plate assays, using cultural as well as culture-independent methods. In liquid medium, AgNPs and AgNO3 inhibited both planktonic growth and biofilm formation. The efficacy of AgNPs and AgNO3 against established, 24 h-old biofilms and planktonic stationary-phase cells was compared by exposure to silver in deionized water. Loss of culturability of planktonic cells was always higher than that of the attached biofilms. However, resuspended biofilm cells became more susceptible to AgNPs and AgNO3 than attached biofilms. Thus, the physical state of bacteria within biofilms rendered them more tolerant to silver compared with the planktonic state. Silver-exposed cells that had become unculturable still displayed signs of viability: they contained rRNA, determined by fluorescent in situ hybridization, as an indicator for potential protein synthesis, maintained their membrane integrity as monitored by differential live/dead staining, and displayed significant levels of adenosine triphosphate. It was concluded that AgNPs and AgNO3 in concentrations at which culturability was inhibited, both planktonic and biofilm cells of P. aeruginosa were still intact and metabolically active, reminiscent of the viable but non-culturable state known to be induced in pathogenic bacteria in response to stress conditions. This observation is important for a realistic assessment of the antimicrobial properties of AgNPs.

Effects of green tea compound epigallocatechin-3-gallate against Stenotrophomonas maltophilia infection and biofilm

We investigated the in vitro and in vivo activities of epigallocatechin-3-gallate (EGCg), a green tea component, against Stenotrophomonas maltophilia (Sm) isolates from cystic fibrosis (CF) patients. In vitro effects of EGCg and the antibiotic colistin (COL) on growth inhibition, survival, and also against young and mature biofilms of S. maltophilia were determined. Qualitative and quantitative changes on the biofilms were assessed by confocal laser scanning microscopy (CLSM). Further, in vivo effects of nebulized EGCg in C57BL/6 and Cftr mutant mice during acute Sm lung infection were evaluated. Subinhibitory concentrations of EGCg significantly reduced not only biofilm formation, but also the quantity of viable cells in young and mature biofilms. CLSM showed that EGCg-exposed biofilms exhibited either a change in total biofilm biovolume or an increase of the fraction of dead cells contained within the biofilm in a dose depended manner. Sm infected wild-type and Cftr mutant mice treated with 1,024 mg/L EGCg by inhalation exhibited significantly lower bacterial counts than those undergoing no treatment or treated with COL. EGCg displayed promising inhibitory and anti-biofilm properties against CF Sm isolates in vitro and significantly reduced Sm bacterial counts in an acute infection model with wild type and CF mice. This natural compound may represent a novel therapeutic agent against Sm infection in CF.

Interaction between extracellular lipase LipA and the polysaccharide alginate of Pseudomonas aeruginosa

Background

As an opportunistic human pathogen Pseudomonas aeruginosa is able to cause acute and chronic infections. The biofilm mode of life significantly contributes to the growth and persistence of P. aeruginosa during an infection process and mediates the pathogenicity of the bacterium. Within a biofilm mucoid strains of P. aeruginosa simultaneously produce and secrete several hydrolytic enzymes and the extracellular polysaccharide alginate. The focus of the current study was the interaction between extracellular lipase LipA and alginate, which may be physiologically relevant in biofilms of mucoid P. aeruginosa.

Results

Fluorescence microscopy of mucoid P. aeruginosa biofilms were performed using fluorogenic lipase substrates. It showed a localization of the extracellular enzyme near the cells. A microtiter plate-based binding assay revealed that the polyanion alginate is able to bind LipA. A molecular modeling approach showed that this binding is structurally based on electrostatic interactions between negatively charged residues of alginate and positively charged amino acids of the protein localized opposite of the catalytic centre. Moreover, we showed that the presence of alginate protected the lipase activity by protection from heat inactivation and from degradation by the endogenous, extracellular protease elastase LasB. This effect was influenced by the chemical properties of the alginate molecules and was enhanced by the presence of O-acetyl groups in the alginate chain.

Conclusion

We demonstrate that the extracellular lipase LipA from P. aeruginosa interacts with the polysaccharide alginate in the self-produced extracellular biofilm matrix of P. aeruginosa via electrostatic interactions suggesting a role of this interaction for enzyme immobilization and accumulation within biofilms. This represents a physiological advantage for the cells. Especially in the biofilm lifestyle, the enzyme is retained near the cell surface, with the catalytic centre exposed towards the substrate and is protected from denaturation and proteolytic degradation.

Efficient computation of interacting model systems

Physiological processes in the human body can be predicted by mathematical models. Medical Decision Support Systems (MDSS) might exploit these predictions when optimizing therapy settings. In critically ill patients depending on mechanical ventilation, these predictions should also consider other organ systems of the human body. In a previously presented framework we combine elements of three model families: respiratory mechanics, cardiovascular dynamics and gas exchange. Computing combinations of moderately complex submodels showed to be computationally costly thus limiting the applicability of those model combinations in an MDSS. A decoupled computing approach was therefore developed, which enables individual evaluation of every submodel. Direct model interaction is not possible in separate calculations. Therefore, interface signals need to be substituted by estimates. These estimates are iteratively improved by increasing model detail in every iteration exploiting the hierarchical structure of the implemented model families. Simulation error converged to a minimum after three iterations. Maximum simulation error showed to be 1.44% compared to the original common coupled computing approach. Simulation error was found to be below measurement noise generally found in clinical data. Simulation time was reduced by factor 34 using one iteration and factor 13 using three iterations. Following the proposed calculation scheme moderately complex model combinations seem to be applicable for model based decision support.

"Candidatus Mesochlamydia elodeae" (Chlamydiae: Parachlamydiaceae), a novel chlamydia parasite of free-living amoebae

Vannella sp. isolated from waterweed Elodea sp. was found infected by a chlamydia-like organism. This organism behaves like a parasite, causing the death through burst of its host. Once the vannellae degenerated, the parasite was successfully kept in laboratory within a Saccamoeba sp. isolated from the same waterweed sample, which revealed in fine through electron microscopy to harbor two bacterial endosymbionts: the chlamydial parasite we introduce and another endosymbiont initially and naturally present in the host. Herein, we provide molecular-based identification of both the amoeba host and its two endosymbionts, with special focus on the chlamydia parasite. High sequence similarity values of the 18S rDNA permitted to assign the amoeba to the species Saccamoeba lacustris (Amoebozoa, Tubulinea). The bacterial endosymbiont naturally harbored by the host belonged to Sphingomonas koreensis (Alpha-Proteobacteria). The chlamydial parasite showed a strict specificity for Saccamoeba spp., being unable to infect a variety of other amoebae, including Acanthamoeba, and it was itself infected by a bacteriophage. Sequence similarity values of the 16S rDNA and phylogenetic analysis indicated that this strain is a new member of the family Parachlamydiaceae, for which we propose the name "Candidatus Mesochlamydia elodeae."

Complementation of Sulfolobus solfataricus PBL2025 with an α-mannosidase: effects on surface attachment and biofilm formation

Compared to Sulfolobus solfataricus P2, the S. solfataricus mutant PBL2025 misses 50 genes (SSO3004-3050), including genes coding for a multitude of enzymes possibly involved in sugar degradation or metabolism. We complemented PBL2025 with two of the missing proteins, the α-mannosidase (SSO3006, Ssα-man) and the β-galactosidase LacS (SSO3019), and performed comparative fluorescence microscopy and confocal laser scanning microscopy to analyze the recombinant strains. We demonstrated that the Ssα-man complemented strain resembled the S. solfataricus P2 behavior with respect to attachment of cells to glass and growth of cells in static biofilms. During expression of the Ssα-man, but not LacS, glucose and mannose-containing extracellular polymeric substance (EPS) levels changed in the recombinant strain during surface attachment and biofilm formation. These results suggest that the Ssα-man might be involved in the modulation of the EPS composition and/or in the de-mannosylation of the glycan tree, which is attached to extracellular glycosylated proteins in S. solfataricus. On the other hand, LacS expression in PBL2025 reduced the carbohydrate content of the isolated total EPS implying a role in the modulation of the produced EPS during static biofilm formation. These are the first enzymes identified as playing a role in archaeal EPS formation.

Biofilms in drinking water and their role as reservoir for pathogens

Most microorganisms on Earth live in various aggregates which are generally termed "biofilms". They are ubiquitous and represent the most successful form of life. They are the active agent in biofiltration and the carriers of the self-cleaning potential in soils, sediments and water. They are also common on surfaces in technical systems where they sometimes cause biofouling. In recent years it has become evident that biofilms in drinking water distribution networks can become transient or long-term habitats for hygienically relevant microorganisms. Important categories of these organisms include faecal indicator bacteria (e.g., Escherichia coli), obligate bacterial pathogens of faecal origin (e.g., Campylobacter spp.) opportunistic bacteria of environmental origin (e.g., Legionella spp., Pseudomonas aeruginosa), enteric viruses (e.g., adenoviruses, rotaviruses, noroviruses) and parasitic protozoa (e.g., Cryptosporidium parvum). These organisms can attach to preexisting biofilms, where they become integrated and survive for days to weeks or even longer, depending on the biology and ecology of the organism and the environmental conditions. There are indications that at least a part of the biofilm populations of pathogenic bacteria persists in a viable but non-culturable (VBNC) state and remains unnoticed by the methods appointed to their detection. Thus, biofilms in drinking water systems can serve as an environmental reservoir for pathogenic microorganisms and represent a potential source of water contamination, resulting in a potential health risk for humans if left unnoticed.

Integration of Pseudomonas aeruginosa and Legionella pneumophila in drinking water biofilms grown on domestic plumbing materials

Drinking water biofilms were grown on coupons of plumbing materials, including ethylene-propylene-diene-monomer (EPDM) rubber, silane cross-linked polyethylene (PE-X b), electron-ray cross-linked PE (PE-X c) and copper under constant flow-through of cold tap water. After 14 days, the biofilms were spiked with Pseudomonas aeruginosa, Legionella pneumophila and Enterobacter nimipressuralis (10(6) cells/mL each). The test bacteria were environmental isolates from contamination events in drinking water systems. After static incubation for 24 h, water flow was resumed and continued for 4 weeks. Total cell count and heterotrophic plate count (HPC) of biofilms were monitored, and P. aeruginosa, L. pneumophila and E. nimipressuralis were quantified, using standard culture-based methods or culture-independent fluorescence in situ hybridization (FISH). After 14 days total cell counts and HPC values were highest on EPDM followed by the plastic materials and copper. P. aeruginosa and L. pneumophila became incorporated into drinking water biofilms and were capable to persist in biofilms on EPDM and PE-X materials for several weeks, while copper biofilms were colonized only by L. pneumophila in low culturable numbers. E. nimipressuralis was not detected in any of the biofilms. Application of the FISH method often yielded orders of magnitude higher levels of P. aeruginosa and L. pneumophila than culture methods. These observations indicate that drinking water biofilms grown under cold water conditions on domestic plumbing materials, especially EPDM and PE-X in the present study, can be a reservoir for P. aeruginosa and L. pneumophila that persist in these habitats mostly in a viable but non-culturable state.

Extracellular enzymes affect biofilm formation of mucoid Pseudomonas aeruginosa

Pseudomonas aeruginosa secretes a variety of hydrolases, many of which contribute to virulence or are thought to play a role in the nutrition of the bacterium. As most studies concerning extracellular enzymes have been performed on planktonic cultures of non-mucoid P. aeruginosa strains, knowledge of the potential role of these enzymes in biofilm formation in mucoid (alginate-producing) P. aeruginosa remains limited. Here we show that mucoid P. aeruginosa produces extracellular hydrolases during biofilm growth. Overexpression of the extracellular lipases LipA and LipC, the esterase EstA and the proteolytic elastase LasB from plasmids revealed that some of these hydrolases affected the composition and physicochemical properties of the extracellular polymeric substances (EPS). While no influence of LipA was observed, the overexpression of estA and lasB led to increased concentrations of extracellular rhamnolipids with enhanced levels of mono-rhamnolipids, elevated amounts of total carbohydrates and decreased alginate concentrations, resulting in increased EPS hydrophobicity and viscosity. Moreover, we observed an influence of the enzymes on cellular motility. Overexpression of estA resulted in a loss of twitching motility, although it enhanced the ability to swim and swarm. The lasB-overexpression strain showed an overall enhanced motility compared with the parent strain. Moreover, the EstA- and LasB-overproduction strains completely lost the ability to form 3D biofilms, whereas the overproduction of LipC increased cell aggregation and the heterogeneity of the biofilms formed. Overall, these findings indicate that directly or indirectly, the secreted enzymes EstA, LasB and LipC can influence the formation and architecture of mucoid P. aeruginosa biofilms as a result of changes in EPS composition and properties, as well as the motility of the cells.

Faecal indicator bacteria in river biofilms

Biofilms in surface waters primarily consist of allochthonous microorganisms. Under conditions of pollution faecally derived bacteria may interact with these biofilms. Total coliform bacteria, Escherichia coli and intestinal enterococci are used to monitor source water quality, indicating faecal pollution and the possible presence of enteric pathogens. In the present study the occurrence of faecal indicators was investigated in biofilms (epilithic biofilms, sediments) of German rivers. All of the biofilms contained significant concentrations of these bacteria, which were several orders of magnitude lower compared with the total cell number and the number of culturable heterotrophic plate count bacteria indicating that faecal indicator bacteria represented a minor fraction of the whole biofilm communities. The biofilms displayed approximately two orders of magnitude higher concentrations of total coliforms, E. coli and enterococci compared with the overlying water. Identification of coliform and enterococcal isolates from the biofilms revealed the presence of species which are known to be opportunistic pathogens. Overall, the results of the present study show that faecal indicator bacteria can survive in the presence of high cell densities of the authochthonous microflora in epilithic biofilms and sediments, suggesting that these biofilms may act as a reservoir for bacterial pathogens in polluted rivers.

Analysis of microbial extracellular polysaccharides in biofilms by HPLC. Part I: Development of the analytical method using two complementary stationary phases

The investigation of microbial extracellular polymeric substances (EPS) is helpful for the implementation of analytical methods which are suitable for biofilm analysis in order to understand the architecture and function of biofilms. A procedure for the qualitative and quantitative determination of various monosaccharides, oligosaccharides and uronic acids as important components of the carbohydrate fraction of microbial EPS by high-performance liquid chromatography (HPLC) and refractive index (RI)/UV detection is presented. Porous graphitic carbon and lead-form cation-exchanger have been examined as stationary phases. Therefore, two complementary HPLC methods are presented. To simulate the conditions of hydrolysis, the influences of various salts, acids and alkalis as matrix components have been investigated. Furthermore, the dependencies on the pH value and temperature of the mobile phase have been thoroughly studied. The results showed that the lead-form cation-exchanger is suitable for the separation of the neutral monosaccharides. However, for direct analysis after acidic hydrolysis with H(2)SO(4), HCl or trifluoroacetic acid, an additional purification step, e.g., precipitation or lyophilization, is necessary when the cation-exchanger is used. With the exception of hydrolysis with HCl, the porous graphitic carbon stationary phase can be used without any further purification step and is appropriate for the separation of uronic acids and their gamma-lactones. Additionally, the separation of a single monosaccharide and its derivatives is possible. Analytical parameters including the sensitivities, repeatabilities, limits of detection and limits of quantification of both HPLC methods using the RI detector are presented. The optimized method has been applied for the characterization of alginates and is also suitable for other extracellular polysaccharides in biofilms.

Detergent-induced cell aggregation in subpopulations of Pseudomonas aeruginosa as a preadaptive survival strategy

During growth of Pseudomonas aeruginosa strain PAO1 with the toxic detergent SDS, a part of the population actively formed macroscopic cell aggregates while the other part grew as freely suspended cells. The physiological function of aggregation for growth with SDS was investigated. Three mutants growing with SDS without aggregation were isolated: the spontaneous mutant strain N and two mutants with transposon insertions in the psl operon for exopolysaccharide synthesis. SDS-induced aggregation in strain N but not in a pslJ mutant was restored by complementation with two genes encoding diguanylate cyclases responsible for synthesis of cyclic-di-guanosine monophosphate (c-di-GMP). By expressing a c-di-GMP-specific phosphodiesterase SDS-induced aggregation of strain PAO1 was reduced. Upon exposure to SDS in the presence of the uncoupler carbonyl cyanide chlorophenylhydrazone, the aggregating strains had ca. 500-fold higher survival rates than the non-aggregating strains. Co-incubation experiments revealed that strain N could integrate into aggregates of strain PAO1 and thereby increase its survival rate more than 1000-fold. These results showed that SDS-induced aggregation involved c-di-GMP signalling with the psl operon as a possible target. Cell aggregation could serve as a pre-adaptive strategy ensuring survival and growth of P. aeruginosa populations in environments with multiple toxic chemicals.

Simultaneous visualisation of biofouling, organic and inorganic particle fouling on separation membranes

Fouling is a major problem in membrane processes of water treatment. It can be caused by the deposition of inorganic and organic particulate material, and of microbial cells which may subsequently form biofilms. In practice, usually more than one foulant participates in the formation of membrane deposits. Knowledge of the composition of fouling layers is important for the development of appropriate countermeasures. For this purpose, an experimental system was established for the generation and microscopic visualisation of mixed deposits, using fluorescently labelled model foulants: (i) drinking-water bacteria stained with nucleic acid-specific dyes (biofouling), (ii) synthetic clay mineral laponite stained with rhodamine 6G (inorganic particle fouling), and (iii) fluorescently labelled polystyrene microspheres (organic particle fouling). Polycarbonate and polyethersulfone membranes were challenged with these foulants by dead-end filtration. On the basis of different fluorescent labels, the single foulants in these mixed deposits could be visualised separately by confocal laser scanning microscopy which, in combination with image analysis, allowed the generation of three-dimensional views of the complete deposits. This method offers the possibility for the estimation of quantitative surface coverage by foulants and for the determination of the efficacy of cleaning measures with respect to the removal of different foulants.

Pseudomonas aeruginosa lectin LecB is located in the outer membrane and is involved in biofilm formation

Pseudomonas aeruginosa is an opportunistic pathogen which causes a variety of diseases, including respiratory tract infections in patients suffering from cystic fibrosis. Therapeutic treatment of P. aeruginosa infections is still very difficult because the bacteria exhibit high intrinsic resistance against a variety of different antibiotics and, in addition, form stable biofilms, e.g. in the human lung. Several virulence factors are produced by P. aeruginosa, among them the two lectins LecA and LecB, which exert different cytotoxic effects on respiratory epithelial cells and presumably facilitate bacterial adhesion to the airway mucosa. Here, the physiology has been studied of the lectin LecB, which binds specifically to L-fucose. A LecB-deficient P. aeruginosa mutant was shown to be impaired in biofilm formation when compared with the wild-type strain, suggesting an important role for LecB in this process. This result prompted an investigation of the subcellular localization of LecB by cell fractionation and subsequent immunoblotting. The results show that LecB is abundantly present in the bacterial outer-membrane fraction. It is further demonstrated that LecB could be released specifically by treatment of the outer-membrane fraction with p-nitrophenyl alpha-L-fucose, whereas treatment with D-galactose had no effect. In contrast, a LecB protein carrying the mutation D104A, which results in a defective sugar-binding site, was no longer detectable in the membrane fraction, suggesting that LecB binds to specific carbohydrate ligands located at the bacterial cell surface. Staining of biofilm cells using fluorescently labelled LecB confirmed the presence of these ligands.

Alginate acetylation influences initial surface colonization by mucoid Pseudomonas aeruginosa

Mucoid strains of Pseudomonas aeruginosa overproduce the exopolysaccharide alginate, which is substituted with O-acetyl groups. Under non-growing conditions in phosphate buffer, a mucoid clinical strain formed microcolonies on steel surfaces, while an acetylation-defective mutant was unable to form cell clusters. Enzymatic degradation of alginate by alginate lyase prevented microcolony formation of the mucoid parent strain. In a continuous-culture flow-cell system, using gluconate minimal medium, the mucoid strain with acetylated alginate formed microcolonies and grew into heterogenous biofilms, whereas the acetylation-defective mutant produced a thinner and more homogeneous biofilm. A lowered viscosity of extracellular material from the acetylation-defective mutant indicated a weakening of exopolymer interactions by loss of acetyl groups. These results suggest that acetyl substituents are necessary for the function of high-molecular-mass alginate to mediate cell aggregation into microcolonies in the early stages of biofilm development by mucoid P. aeruginosa, thereby determining the architecture of the mature biofilm.

Use of an oxonol dye in combination with confocal laser scanning microscopy to monitor damage to Staphylococcus aureus cells during colonisation of silver-coated vascular grafts

The antimicrobial silver-coating of medical prostheses is regarded as a means to reduce the risk of bacterial colonisation after implantation. The effect of a silver-coating of vascular grafts on biofilm formation was assessed in batch cultures of Staphylococcus aureus, using confocal laser scanning microscopy. Total cells in biofilms were analysed by staining with the DNA-binding fluorochrome SYTO 62 and the proportion of damaged cells was quantified with the membrane potential-sensitive dye bis-(1,3-dibutylbarbituric acid) trimethine oxonol. Both the extent of biofilm formation and the proportion of viable biofilm cells were significantly diminished on the surface of the silver-coated vascular grafts compared with uncoated controls, probably due to the antimicrobial activity of silver ions released from the silver-coated graft surface.

Metagenome survey of biofilms in drinking-water networks

Most naturally occurring biofilms contain a vast majority of microorganisms which have not yet been cultured, and therefore we have little information on the genetic information content of these communities. Therefore, we initiated work to characterize the complex metagenome of model drinking water biofilms grown on rubber-coated valves by employing three different strategies. First, a sequence analysis of 650 16S rRNA clones indicated a high diversity within the biofilm communities, with the majority of the microbes being closely related to the Proteobacteria: Only a small fraction of the 16S rRNA sequences were highly similar to rRNA sequences from Actinobacteria, low-G+C gram-positives and the Cytophaga-Flavobacterium-Bacteroides group. Our second strategy included a snapshot genome sequencing approach. Homology searches in public databases with 5,000 random sequence clones from a small insert library resulted in the identification of 2,200 putative protein-coding sequences, of which 1,026 could be classified into functional groups. Similarity analyses indicated that significant fractions of the genes and proteins identified were highly similar to known proteins observed in the genera Rhizobium, Pseudomonas, and Escherichia: Finally, we report 144 kb of DNA sequence information from four selected cosmid clones, of which two formed a 75-kb overlapping contig. The majority of the proteins identified by whole-cosmid sequencing probably originated from microbes closely related to the alpha-, beta-, and gamma-Proteobacteria: The sequence information was used to set up a database containing the phylogenetic and genomic information on this model microbial community. Concerning the potential health risk of the microbial community studied, no DNA or protein sequences directly linked to pathogenic traits were identified.

Interaction between alginates and manganese cations: identification of preferred cation binding sites

Algal and bacterial alginates have been studied by means of 13C NMR spectroscopy in presence of paramagnetic manganese ions in order to reveal the nature of their interaction with bivalent cations. It is found that the mannuronate blocks bind manganese cations externally near their carboxylate groups, while guluronate blocks show the capability to integrate Mn2+ into pocket-like structures formed by adjacent guluronate residues. In alternating mannuronate-guluronate blocks, manganese ions preferentially locate in a concave structure formed by guluronate-mannuronate pairs. Partial acetylation of the alginate generally reduces its capability to interact with bivalent cations, however, the selectivity of the binding geometry is conserved. The results may serve as a hint for the better understanding of the alginate gelation in presence of calcium ions.

Contamination of drinking water by coliforms from biofilms grown on rubber-coated valves

In water samples from drinking water distribution systems, coliform bacteria (predominantly Citrobacter species) were repeatedly detected. Disinfection and flushing of the systems did not erase the problem. The pattern of the coliform occurrences indicated contamination originating from biofilms. After inspection of internal surfaces of the systems, no significant biofilm growth was observed on pipe surfaces, but in a number of cases, visible biofilms were detected on rubber-coated valves which harboured the same coliform species as those found in the drinking water samples. In these cases, the rubber-coated valves seemed to act as point sources for the contamination of water.

Contamination potential of drinking water distribution network biofilms

Drinking water distribution system biofilms were investigated for the presence of hygienically relevant microorganisms. Early biofilm formation was evaluated in biofilm reactors on stainless steel, copper, polyvinyl chloride (PVC) and polyethylene coupons exposed to unchlorinated drinking water. After 12 to 18 months, a plateau phase of biofilm development was reached. Surface colonization on the materials ranged between 4 x 10(6) and 3 x 10(7) cells/cm2, with heterotrophic plate count (HPC) bacteria between 9 x 10(3) and 7 x 10(5) colony-forming units (cfu)/cm2. Established biofilms were investigated in 18 pipe sections (2 to 99 years old) cut out from distribution pipelines. Materials included cast iron, galvanized steel, cement and PVC. Colonization ranged from 4 x 10(5) to 2 x 10(8) cells/cm2, HPC levels varied between 1 and 2 x 10(5) cfu/cm2. No correlation was found between extent of colonization and age of the pipes. Using cultural detection methods, coliform bacteria were rarely found, while Escherichia coli, Pseudomonas aeruginosa and Legionella spp. were not detected in the biofilms. In regular operation, distribution system biofilms do not seem to be common habitats for pathogens. However, nutrient-leaching materials like rubber-coated valves were observed with massive biofilms which harboured coliform bacteria contaminating drinking water.

Application of fluorescently labelled lectins for the visualization and biochemical characterization of polysaccharides in biofilms of Pseudomonas aeruginosa

Fluorescently labelled lectins were used in combination with epifluorescence microscopy and confocal laser scanning microscopy to allow the visualization and characterization of carbohydrate-containing extracellular polymeric substances (EPS) in biofilms of Pseudomonas aeruginosa. A mucoid strain characterized by an overproduction of the exopolysaccharide alginate, and an isogenic, non-mucoid strain were used. Model biofilms grown on polycarbonate filters were treated with lectins concanavalin A (ConA) and wheat germ agglutinin (WGA) that were fluorescently labelled with fluorescein isothiocyanate or tetramethyl rhodamine isothiocyanate. Fluorescently labelled ConA yielded cloud-like regions that were heterogeneously distributed within mucoid biofilms, whereas these structures were only rarely present in biofilms of the non-mucoid strain. The bacteria visualized with the fluorochrome SYTO 9 were localized both within and between the ConA-stained regions. In WGA-treated biofilms, the lectin was predominantly associated with bacterial cells. Alginate seemed to be involved in the interaction of ConA with the EPS matrix, since (i) pre-treatment of biofilms with an alginate lyase resulted in a loss of ConA biofilm staining, and (ii) using an enzyme-linked lectinsorbent assay (ELLA), ConA was shown to bind to purified alginate, but not to alginate that was degraded by alginate lyase. The application of fluorescently labelled lectins in combination with ELLA was found to be useful for the visualization and characterization of extracellular polysaccharide structures in P. aeruginosa biofilms.

Monomer composition and sequence of alginates from Pseudomonas aeruginosa

Alginates from four strains of Pseudomonas aeruginosa, one mucoid strain isolated from a technical water system, one strain isolated from a patient with cystic fibrosis and two mutants of this strain with a defect which affects the O-acetylation of the extracellular alginate, have been isolated and analysed for monomer composition and sequence by 13C-nuclear magnetic resonance (NMR) spectroscopy. The detected contributions of different monomer triplets (triads) were compared with values expected from a statistical chain constitution based on the given monomer ratio. While a typical algal alginate presents a nearly statistical distribution of uronic acids in the polymer chain, a strong deviation from the statistical arrangement of mannuronate (M) and guluronate (G) was found in the alginate of the mucoid strains of P. aeruginosa, being most expressed for the triad MMM. This feature is partially lost in the alginate from the mutant strains, indicating that the O-acetylation is linked to a mechanism which takes influence on the chain sequence. The strong preference for MG-pairs in the parent strain of P. aeruginosa may be connected to a stronger binding of cations in the MG-vicinity.

Influence of extracellular polymeric substances on deposition and redeposition of Pseudomonas aeruginosa to surfaces

In this study, the role of extracellular polymeric substances (EPS) in the initial adhesion of EPS-producing Pseudomonas aeruginosa SG81 and SG81R1, a non-EPS-producing strain, to substrata with different hydrophobicity was investigated. The release of EPS by SG81 was concurrent with a decrease in surface tension of a bacterial suspension from 70 to 45 mJ m(-2) that was absent for SG81R1. Both strains adhered faster and in higher numbers to a hydrophilic than to a hydrophobic substratum, but the initial deposition rates and numbers of adhering bacteria in a stationary-end point were highest for the non-EPS-producing strain SG81R1, regardless of substratum hydrophobicity. Both strains adhered less to substrata pre-coated with isolated EPS of strain SG81. Furthermore, it was investigated whether bacteria, detached by passing air-bubbles, had left behind 'footprints' with an influence on adhesion of newly redepositing bacteria. Redeposition on glass was highest for non-EPS-producing SG81R1 and decreased linearly with the number of times these cycles of detachment and deposition were repeated to become similar to the redeposition of SG81 after six cycles. This indicates that P. aeruginosa SG81 leaves the substratum surface nearly completely covered with EPS after detachment, while SG81R1 releases only minor amounts of surface active EPS, completely covering the substratum after repeated cycles of detachment and adhesion. Atomic force microscopy showed a thick and irregular EPS layer (up to 32 nm) after the first detachment cycle of EPS-producing strain SG81, whereas the putatively non-EPS-producing strain SG81R1 left a 9 nm thin layer after one cycle. X-ray photoelectron spectroscopy indicated that the bacterial footprints consisted of uronic acids, the prevalence of which increased with the number of detachment and deposition cycles.

Capability of mucoid Pseudomonas aeruginosa to survive in chlorinated water

Mucoid strains of Pseudomonas aeruginosa are characterized by an overproduction of the extracellular polysaccharide alginate. When suspended into chlorinated swimming-pool water or drinking water samples, mucoid bacteria revealed enhanced survival compared with isogenic nonmucoid cells. Removal of slime from mucoid bacteria abolished chlorine resistance, addition of purified alginate to washed bacteria again enhanced survival. Thus, alginate-containing slime confers protection on P. aeruginosa against chlorine and may contribute to survival of these bacteria in chlorinated water systems.

Uniaxial compression measurement device for investigation of the mechanical stability of biofilms

The mechanical stability of biofilms is important for biotechnology, as sloughing of the biomass due to mechanical failure of the biofilm matrix can lead to severe interferences with biofilm processes. In cases of biofouling, biofilms have to be removed, in which case their mechanical stability must be overcome. The apparent modulus of elasticity and the yield strength as obtained from uniaxial compression experiments can be taken as parameters indicative for the mechanical stability of a biofilm. A film rheometer is presented which allows for the determination of these quantities, using model biofilms of Pseudomonas aeruginosa grown on membrane filters. The compressive stress-strain behaviour up to the point of failure is recorded at a compression speed of 1 microm s(-1). In accordance with the stress-strain curve, the investigated biofilm can be described as viscoelastic material, which demonstrates plastic flow properties. The extracellular polymeric substances (EPS), which keep biofilms together, form a temporary network of fluctuating junction points. Above the yield point, the gel structure fails and the system behaves as a highly viscous fluid. The apparent modulus of elasticity and the yield point are considered to be useful parameters for characterizing the mechanical properties of biofilms.

Relevance of microbial extracellular polymeric substances (EPSs)--Part II: Technical aspects

Extracellular polymeric substances (EPSs) are involved in both detrimental and beneficial consequences of microbial aggregates such as biofilms, flocs and biological sludges. In biofouling, they are responsible for the increase of friction resistance, change of surface properties such as hydrophobicity, roughness, colour, etc. In biocorrosion of metals they are involved by their ability to bind metal ions. In bioweathering, they contribute by their complexing properties to the dissolution of minerals. The EPSs represent a sorption site for pollutants such as heavy metal ions and organic molecules. This can lead to a burden in wastewater sludge; on the other hand, the sorption properties can be used for water purification. Other biotechnological uses of EPS exploit their contribution to viscosity, e.g., in food, paints and oil-drilling 'muds'; their hydrating properties are also used in cosmetics and pharmaceuticals. Furthermore, EPSs may have potential uses as biosurfactants, e.g., in tertiary oil production, and as biological glue. EPSs are an interesting component of all biofilm systems and still hold a large biotechnological potential.