Effects of Photochemical Transformations of Dissolved Organic Matter on Bacterial Metabolism and Diversity in Three Contrasting Coastal Sites in the Northwestern Mediterranean Sea during Summer |
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Authors: | M Abboudi W H Jeffrey J-F Ghiglione M Pujo-Pay L Oriol R Sempéré B Charrière F Joux |
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Institution: | (1) CNRS, UMR 7621, Université Pierre et Marie Curie-Paris-6, 66650 Banyuls-sur-mer, France;(2) Laboratoire de Microbiologie Géochimie et Ecologie Marines (LMGEM), CNRS/INSU, UMR 6117, Centre d’Océanologie de Marseille, Université de la Méditerranée, Campus de Luminy, Case 901, 13288 Marseille Cedex 9, France;(3) Center for Environmental Diagnostics and Bioremediation, University of West Florida, 11000 University Parkway, Pensacola, FL 32561, USA;(4) Observatoire Océanologique de Banyuls. Laboratoire d’Océanographie Biologique de Banyuls, Université Paris VI, CNRS UMR 7621, BP44, 1, Avenue du Fontaulé, 66650 Banyuls-sur-Mer Cedex, France |
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Abstract: | The effects of phototransformation of dissolved organic matter (DOM) on bacterial growth, production, respiration, growth
efficiency, and diversity were investigated during summer in two lagoons and one oligotrophic coastal water samples from the
Northwestern Mediterranean Sea, differing widely in DOM and chromophoric DOM concentrations. Exposure of 0.2-μm filtered waters
to full sun radiation for 1 d resulted in small changes in optical properties and concentrations of DOM, and no changes in
nitrate, nitrite, and phosphate concentrations. After exposure to sunlight or dark (control) treatments, the water samples
were inoculated with the original bacterial community. Phototransformation of DOM had contrasting effects on bacterial production
and respiration, depending on the water’s origin, resulting in an increase of bacterial growth efficiency for the oligotrophic
coastal water sample (120%) and a decrease for the lagoon waters (20 to 40%) relative to that observed in dark treatments.
We also observed that bacterial growth on DOM irradiated by full sun resulted in changes in community structure of total and
metabolically active bacterial cells for the three locations studied when compared to the bacteria growing on un-irradiated
DOM, and that changes were mainly caused by phototransformation of DOM by UV radiation for the eutrophic lagoon and the oligotrophic
coastal water and by photosynthetically active radiation (PAR) for the mesoeutrophic lagoon. These initial results indicate
that phototransformation of DOM significantly alters both bacterial metabolism and community structure in surface water for
a variety of coastal ecosystems in the Mediterranean Sea. Further studies will be necessary to elucidate a more detailed appreciation
of potential temporal and spatial variations of the effects measured. |
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