Seasonal variations of the composition of microbial biofilms in sandy tidal flats: Focus of fatty acids, pigments and exopolymers

Abstract

Biofilms, or microbial mats, are common associations of microorganisms in tidal flats; they generally consist of a large diversity of organisms embedded in a matrix of Extracellular Polymeric Substances (EPS). These molecules are mainly composed of carbohydrates and proteins, but their detailed monomer compositions and seasonal variations are currently unknown. Yet this composition determines the numerous roles of biofilms in these systems.This study investigated the changes in composition of carbohydrates in intertidal microbial mats over a year to decipher seasonal variations in biofilms and in varying hydrodynamic conditions. This work also aimed to assess how these compositions are related to microbial assemblages. In this context, natural biofilms whose development was influenced or not by artificial structures mimicking polychaete tubes were sampled monthly for over a year in intertidal flats of the Chausey archipelago. Biofilms were compared through the analysis of their fatty acid and pigment contents, and the monosaccharide composition of their EPS carbohydrates. Carbohydrates from both colloidal and bound EPS contained mainly glucose and, to a lower extent, galactose and mannose but they showed significant differences in their detailed monosaccharide compositions. These two fractions displayed different seasonal evolution, even if glucose accumulated in both fractions in summer; bound EPS only were affected by artificial biogenic structures. Sediment composition in fatty acids and pigments showed that microbial communities were dominated by diatoms and heterotrophic bacteria.Their relative proportions, as well as those of other groups like cryptophytes, changed between times and treatments. The changes in EPS composition were not fully explained by modifications of microbial assemblages but also depended on the processes taking place in sediments and on environmental conditions. These variations of EPS compositions are likely to alter different ecosystem processes such as biostabilisation or pollutants trapping.

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“…EPSs producing isolates were screened by Calcofluor white dye which is fast EPSs detecting method. As reported by Kaufusi et al, (2004) 35 , who studied the detection of EPSs using this dye, change fluorescence negative colonies can easily be identified. Further confirmatory screening assays were done by other dyes viz., Congo-red and Trypan-blue, is known to interact with β-(1-3) -and β-(1-4) -glucans and was successfully used to identify biofilm formation by EPSs from different Staphylococci strains.…”

Use of glucose biosensors to measure extracellular glucose exudation by intertidal microphytobenthos in southern Tasmania

“…, Passarelli et al. ). While extracellular carbohydrate production occurs in both light and dark, much of the light‐weight fraction, principally comprised of monosaccharides such as glucose, is associated with photosynthesis (Underwood and Paterson , Smith and Underwood ).…”

“…3) and this was similar for all cultured species and the natural communities. Glucose can comprise more than 70% of the total extracellular carbohydrate produced by MPB and is associated with overflow metabolism (Smith and Underwood 2000, De Brouwer and Stal 2001, 2002, Hama and Yanagi 2001, Cook et al 2007, Hass and Wild 2010, Pierre et al 2014, Passarelli et al 2015. While extracellular carbohydrate production occurs in both light and dark, much of the light-weight fraction, principally comprised of monosaccharides such as glucose, is associated with photosynthesis (Underwood andPaterson 2003, Smith andUnderwood 1998).…”

The effect of cyclic variation of shear stress on non‐cohesive sediment stabilization by microbial biofilms: the role of ‘biofilm precursors’

“…Despite the many studies that have investigated biofilms in situ (Underwood and Paterson, 1993;de Winder et al, 1999;Montanie et al, 2014;Orvain et al, 2014;Passarelli et al, 2015), much of our understanding has come from laboratory experiments (Orvain et al, 2003;Tolhurst et al, 2008;Hagadorn and Mcdowell, 2012). Most laboratory experiments tended to examine biofilm growth under steady shear stresses (Chao et al, 2014;Cochero et al, 2015).…”