Visualization and analysis of EPS glycoconjugates of the thermoacidophilic archaeon Sulfolobus metallicus.

Biofilms are surface-associated colonies of microorganisms embedded in a matrix of extracellular polymeric substances (EPS). As EPS mediate the contact between cells and surfaces, an understanding of their composition and production is of particular interest. In this study, the EPS components of Sulfolobus metallicus DSM 6482(T) forming biofilms on elemental sulfur (S(0)) were investigated by confocal laser scanning microscopy (CLSM). In order to visualize cell and EPS distributions, biofilm cells were stained with various dyes specific for glycoconjugates, proteins, nucleic acids and lipids. Biofilm cells on S(0) were heterogeneously distributed and characterized as individual cells, microcolonies, and large clusters up to a hundred micrometers in diameter. The glycoconjugates in biofilms were detected by fluorescence lectin-binding analysis (FLBA). Screening of 72 commercially available lectins resulted in the selection of 21 lectins useful for staining biofilms of S. metallicus (T). Capsular EPS from planktonic cells were mainly composed of carbohydrates and proteins. In contrast, colloidal EPS from planktonic cells were dominated by carbohydrates. Proteins were found to be major components in EPS from biofilms on S(0). Using specific probes combined with CLSM, we showed that extracellular proteins and nucleic acids were present in the EPS matrix. Finally, we showed that S. metallicus (T) cells were embedded in a flexible EPS matrix. This study provides new insights into archaeal biofilms and EPS composition and properties with respect to their interactions with S(0).

Visualizing the dental biofilm matrix by means of fluorescence lectin-binding analysis.

The extracellular matrix is a poorly studied, yet important component of dental biofilms. Fluorescence lectin-binding analysis (FLBA) is a powerful tool to characterize glycoconjugates in the biofilm matrix. This study aimed to systematically investigate the ability of 75 fluorescently labeled lectins to visualize and quantify extracellular glycoconjugates in dental biofilms. Lectin binding was screened on pooled supragingival biofilm samples collected from 76 subjects using confocal microscopy. FLBA was then performed with 10 selected lectins on biofilms grown in situ for 48 h in the absence of sucrose. For five lectins that proved particularly suitable, stained biovolumes were quantified and correlated to the bacterial composition of the biofilms. Additionally, combinations of up to three differently labeled lectins were tested. Of the 10 lectins, five bound particularly well in 48-h-biofilms: Aleuria aurantia (AAL), Calystega sepiem (Calsepa), Lycopersicon esculentum (LEA), Morniga-G (MNA-G) and Helix pomatia (HPA). No significant correlation between the binding of specific lectins and bacterial composition was found. Fluorescently labeled lectins enable the visualization of glycoconjugates in the dental biofilm matrix. The characterization and quantification of glycoconjugates in dental biofilms require a combination of several lectins. For 48-h-biofilms grown in absence of sucrose, AAL, Calsepa, HPA, LEA, and MNA-G are recommendable.

The composition and compression of biofilms developed on ultrafiltration membranes determine hydraulic biofilm resistance.

This study aimed at identifying how to improve the level of permeate flux stabilisation during gravity-driven membrane filtration without control of biofilm formation. The focus was therefore on understanding (i) how the different fractions of the biofilms (inorganics particles, bacterial cells, EPS matrix) influence its hydraulic resistance and (ii) how the compression of biofilms impacts its hydraulic resistance, i.e., can water head be increased to increase the level of permeate flux stabilisation. Biofilms were developed on ultrafiltration membranes at 88 and 284 cm water heads with dead-end filtration for around 50 days. A larger water head resulted in a smaller biofilm permeability (150 and 50 L m(-2) h(-1) bar(-1) for biofilms grown at 88 cm and 284 cm water head, respectively). Biofilms were mainly composed of EPS (>90% in volume). The comparison of the hydraulic resistances of biofilms to model fouling layers indicated that most of the hydraulic resistance is due to the EPS matrix. The compressibility of the biofilm was also evaluated by subjecting the biofilms to short-term (few minutes) and long-term variations of transmembrane pressures (TMP). A sudden change of TMP resulted in an instantaneous and reversible change of biofilm hydraulic resistance. A long-term change of TMP induced a slow change in the biofilm hydraulic resistance. Our results demonstrate that the response of biofilms to a TMP change has two components: an immediate variation of resistance (due to compression/relaxation) and a long-term response (linked to biofilm adaptation/growth). Our results provide relevant information about the relationship between the operating conditions in terms of TMP, the biofilm structure and composition and the resulting biofilm hydraulic resistance. These findings have practical implications for a broad range of membrane systems.