Bacterial dynamics in a microphytobenthic biofilm: A tidal mesocosm approach

Abstract

In intertidal mudflats, during low tide exposure, microphytobenthos (MPB) migrate vertically through the surface sediment and form, with the heterotrophic bacteria, a transient biofilm. Inside this biofilm, multiple interactions exist between MPB and bacteria. These micro-organisms secrete a wide range of extracellular polymeric substances (EPS), which are major components of the biofilm matrix. In this study, we used a tidal mesocosm experiment in order to decipher the interactions of the MPB-EPS-bacteria complex within the biofilm. We tried to determine if the EPS could control bacterial activities and/or production and/or richness according to the age of the biofilm and to the immersion/emersion period. The dynamics of biomasses of MPB and prokaryotes, the bacterial production, the hydrolysis of predominating organic constituents in the dissolved organic carbon (DOC) pool (i.e., carbohydrates and polypeptides), and the bacterial structure were studied in relation to the different EPS fractions (carbohydrates and proteins: colloidal and bound) dynamics during 8 days. Our experiment had emphasized the influence of the environmental conditions (light, immersion/emersion) on the interactions within the biofilm and also on the effects on biofilm ageing. Bacterial production was always inhibited by the bound EPS-carbohydrate, especially during low tide. Our results suggest that the concentration and composition of EPS had a major role in the bacterial/MPB interactions: these interactions can be either positive or negative in order to regulate the productive phases of MPB and bacteria.

Tidal and seasonal effects on the short-term temporal patterns of bacteria, microphytobenthos and exopolymers in natural intertidal biofilms (Brouage, France)

“…In winter, the monomeric composition of bound EPS is especially enriched in deoxy sugars (Pierre et al, 2014). This specific richness in deoxy sugar of bound EPS carbohydrates was previously observed in literature (Giroldo et al, 2003;Takahashi et al, 2009) and this specific composition could be implied in a negative interaction between both microorganisms as it has been put in evidence in a mesocosm study (Agogué et al, 2014). EPS have already been described as a bacterial development regulator (Lubarsky et al, 2010;Smith et al, 1995) or more precisely as an inhibitor of bacterial development (Smith et al, 1995).…”

Influence of tubificid worms on sediment structure, benthic biofilm and fauna in wetlands: A field enclosure experiment

“…The comparison between this study and these previous laboratory experiments therefore suggests that enhanced bacterial abundance and microbial enzymatic activities with bioturbators can be accentuated by the presence of algae. We can speculate that the positive even if not significant influence of worms on algal biomass increased the algal hydrolytic activity but also the supply of labile organic carbon (algal secretion during photosynthesis) directly available for the bacterial compartment (Agogué et al., ; Chrost, ; Makk, Acs, Marialigeti, & Kovacs, ). Nevertheless, more experiments are needed to evaluate the links between the two components of the biofilm (algae and bacteria) and the worm activities.…”

Biofilm origin of clay-coated sand grains

“…EPS (colloquially known as bio-glue and mucilage; Agogué et al, 2014;Higgins et al, 2003) is produced within intertidal siliciclastic estuarine settings by epipelic diatoms for a variety of functions (Decho, 1990). One function of EPS is to facilitate the vertical movement of diatoms, which colonize the sediment in response to tidal and daylight cycles, for photosynthetic purposes and to maintain optimum environmental conditions (Hoagland et al, 1993;Stal, 2003).…”