Proliferation of purple sulphur bacteria at the sediment surface affects intertidal mat diversity and functionality

Funding provided by French National Centre for Scientific Research/INSU program EC2CO-MicroBien (Microbiologie Environnementale -BIOPOURPRE Project), European Community (ASSEMBLE grant agreement n° 227799), Region Pays de la Loire (France), Marine Alliance for Science and Technology for Scotland and the Scottish Funding Council and participating institutions.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.Publisher PDFPeer reviewe

The Family Chromatiaceae

The Chromatiaceae is a family of the Chromatiales within the Gammaproteobacteria and closely related to the Ectothiorhodospiraceae. Representatives of both families are referred to as phototrophic purple sulfur bacteria and typically grow under anoxic conditions in the light using sulfide as photosynthetic electron donor, which is oxidized to sulfate via intermediate accumulation of globules of elemental sulfur. In Chromatiaceae species, the sulfur globules appear inside the cells; in Ectothiorhodospiraceae, they are formed outside the cells and appear in the medium. Characteristic properties of these bacteria are the synthesis of photosynthetic pigments, bacteriochlorophyll a or b, and various types of carotenoids and the formation of a photosynthetic apparatus with reaction center and antenna complexes localized within internal membrane systems. Phototrophic growth, photosynthetic pigment synthesis, and formation of the photosynthetic apparatus and internal membranes are strictly regulated by oxygen and light and become derepressed at low oxygen tensions. Typically, Chromatiaceae are enabled to the photolithoautotrophic mode of growth. A number of species also can grow photoheterotrophically using a limited number of simple organic molecules. Some species also can grow under chemotrophic conditions in the dark, either autotrophically or heterotrophically using oxygen as terminal electron acceptor in respiratory processe