Biofilm polymers: relationship between carbohydrate biopolymers from estuarine mudflats and unialgal cultures of benthic diatoms

Abstract

Benthic microalgae (microphytobenthos) are the dominant group of primary producers in many marine intertidal and subtidal habitats. Estuarine mudflat diatoms are thought to be major contributors of extracellular polymeric substances (EPS), which are important for sediment stabilization and in benthic food chains. Biofilms from 6 sites in the Colne estuary, UK, were fractionated to isolate biopolymers (colloidal, colloidal EPS [cEPS], low molecular weight [LMW] carbohydrates, hot water [HW] and hot bicarbonate [HB] soluble) and the same techniques were applied to diatoms cultured from these sediments. At sites dominated by benthic diatoms, colloidal carbohydrate concentration and chlorophyll a were closely related. With increasing biomass, the proportion of cEPS within the colloidal fraction decreased from 60 to 20%. Carbohydrate analysis revealed significant differences in monosaccharide and uronic acid composition of different carbohydrate fractions. Principal component analysis (PCA) of monosaccharide composition of HB polymers from both field and culture samples grouped closely along fucose and rhamnose vectors and formed 2 distinct clusters. HW and LMW fractions grouped along the glucose vector and cEPS polymers along the galactose and arabinose vectors. These data indicate that the simple relationship between colloidal carbohydrate concentration and microphytobenthic biomass in biofilms masks a high degree of potential complexity within the sediment carbohydrate pool and in the different proportions of polymeric and nonpolymeric material between different biofilms. Comparing monosaccharide composition of extracts generated using the same protocol, natural assemblages showed close relationships with unialgal cultures, confirming the important role of diatom-derived polymers in mudflat ecology. KEY WORDS: Diatoms · Biofilms · Microphytobenthos · EPS · Monosaccharide distribution · Uronic acids · Biopolymers · Fractionation Resale or republication not permitted without written consent of the publisherAquat Microb Ecol 38: [169][170][171][172][173][174][175][176][177][178][179][180] 2005 1993, . Many benthic diatoms exhibit patterns of vertical migration which allow cells to move into the narrow photic zone present in the top few millimeters of sediment, and this diatom motility is closely linked to EPS production (Lind et al. 1997. The postulated role of EPS in the ecosystem includes biostabilisation of sediments (Paterson 1986), a carbon source for benthic and planktonic species (Decho 1990, Underwood & Smith 1998a, and in mediating species interactions (Hoagland et al. 1993).Correlations have been measured between algal biomass (chlorophyll a [chl a] concentration) and colloidal (water-soluble) carbohydrate concentrations in estuarine sediments (Underwood & Paterson 1993, Underwood & Smith 1998b. These observations led to the publication of a model describing the relationship between sediment chl a and colloidal carbohydrate concentrations, developed using data from a number of European estuar...

Does sediment grain size affect diatom grazing by harpacticoid copepods?

“…We estimated that an average of 125,000 diatom cells/copepod would correspond to food limitation, so there was suYcient food available in our experimental units. There were no data on diatom concentration in the Weld situation, however it is well known that diatom bioWlms are well-established on intertidal mudXats (e.g., Bellinger, Abdullahi, Gretz, & Underwood, 2005;Decho, 2000;Herlory, Guarini, Richard, & Blanchard, 2004) though these bioWlms are very variable depending on light conditions (pers. observ.…”

“…The EPS matrix of bioWlm forms sticky coatings on individual sediment particles and detrital surfaces, which act as a stabilizing anchor to buVer cells and their extracellular processes during frequent physical stresses (e.g., changes in salinity and temperature, UV irradiation, desiccation) (Decho, 2000). Especially intertidal mudXats, where the test harpacticoid species were collected from, are known for these extended bioWlms of microphytobenthos (e.g., Bellinger et al, 2005Decho, 2000Herlory et al, 2004).…”

Dissolved organic matter (DOM) release by phytoplankton in the contemporary and future ocean

“…TEP plays an important role in the biogeochemistry of the biological carbon pump (Passow & Carlson, 2012) and consequently there is a need to better define its composition to determine its origin and biogeochemical significance. Much of the recent detailed work on the composition of EPS produced by diatoms has been conducted with laboratory-grown cultures of benthic epipelic diatoms (Underwood et al, 2004;Bellinger et al, 2005;Abdullahi et al, 2006). There is no reason why the techniques used in this research could not be applied to ecologically relevant taxa of phytoplankton.…”

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Ecological role of exopolysaccharides of Bacillariophyta: A review

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