No 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.

No abstract

There is a relative absence of studies dealing with mats of purple sulphur bacteria in the intertidal zone. These bacteria display an array of metabolic pathways that allow them to disperse and develop under a wide variety of conditions, making these mats important in terms of ecosystem processes and functions. Mass blooms of purple sulphur bacteria develop during summer on sediments in the intertidal zone especially on macroalgal deposits. The microbial composition of different types of mats differentially affected by the development of purple sulphur bacteria was examined, at low tide, using a set of biochemical markers (fatty acids, pigments) and composition was assessed against their influence on ecosystem functions (sediment cohesiveness, CO2 fixation). We demonstrated that proliferation of purple sulphur bacteria has a major impact on intertidal mats diversity and functions. Indeed, assemblages dominated by purple sulphur bacteria (Chromatiaceae) were efficient exopolymer producers and their biostabilisation potential was significant. In addition, the massive growth of purple sulphur bacteria resulted in a net CO2 degassing whereas diatom dominated biofilms represented a net CO2 sink.

Using a 15-min High Performance Liquid Chromatography (HPLC) elution program, the current study compared pigment extraction efficiencies in aerobic anoxygenic phototrophic bacteria (AAPB; Dinoroseobacter shibae, Roseobacter denitrificans, Erythrobacter longus, and a strain of Rhodovulum sp. isolated from Tagus estuarine intertidal sediments -SPS1025 T ) using four extraction times (15, 30, 60, and 120 min) and three solvents (acetone, acetone/methanol, and methanol). Overall, increasing extraction time showed no significant effect on bacteriochlorophyll a (BChl a) and carotenoid extraction efficiencies in all strains. BChl a extraction efficiency was significantly higher in the mixture acetone/methanol and methanol, but methanol induced significantly higher BChl a degradation for all strains. Carotenoid extraction efficiencies were dependent on solvent and pigment polarity. Non-polar carotenoids were better extracted with acetone and polar carotenoids with methanol. We suggest the application of the used HPLC procedure for the quantification of photosynthetic pigments in AAPB due to its high sample throughput and peak resolution. We also recommend the use acetone/methanol for extraction of AAPB photosynthetic pigments with extraction periods of 15 min to achieve higher BChl a extraction yields and minimize carotenoid degradation.