title: Warming-induced changes in denitrifier community structure modulate the ability of phototrophic river biofilms to denitrify.
abstract: Microbial denitrification is the main nitrogen removing process in freshwater ecosystems. The aim of this study was to show whether and how water warming (+2.5 °C) drives bacterial diversity and structuring and how bacterial diversity affects denitrification enzymatic activity in phototrophic river biofilms (PRB). We used water warming associated to the immediate thermal release of a nuclear power plant cooling circuit to produce natural PRB assemblages on glass slides while testing 2 temperatures (mean temperature of 17 °C versus 19.5 °C). PRB were sampled at 2 sampling times during PRB accretion (6 and 21days) in both temperatures. Bacterial community composition was assessed using ARISA. Denitrifier community abundance and denitrification gene mRNA levels were estimated by q-PCR and qRT-PCR, respectively, of 5 genes encoding catalytic subunits of the denitrification key enzymes. Denitrification enzyme activity (DEA) was measured by the acetylene-block assay at 20 °C. A mean water warming of 2.5 °C was sufficient to produce contrasted total bacterial and denitrifier communities and, therefore, to affect DEA. Indirect temperature effect on DEA may have varied between sampling time, increasing by up to 10 the denitrification rate of 6-day-old PRB and decreasing by up to 5 the denitrification rate of 21-day-old PRB. The present results suggest that indirect effects of warming through changes in bacterial community composition, coupled to the strong direct effect of temperature on DEA already demonstrated in PRB, could modulate dissolved nitrogen removal by denitrification in rivers and streams.
authors: Université de Toulouse, UPS, INP, EcoLab (Laboratoire Ecologie Fonctionnelle et Environnement), 118 route de Narbonne, F-31062 Toulouse, France; CNRS, EcoLab, F-31062 Toulouse, France. Electronic address: stephanie.bouletreau@univ-tlse3.fr.
authors: Stéphanie
authors: S
authors: Boulêtreau
authors: Emilie
authors: E
authors: Lyautey
authors: Sophie
authors: S
authors: Dubois
authors: Arthur
authors: A
authors: Compin
authors: Cécile
authors: C
authors: Delattre
authors: Aurélie
authors: A
authors: Touron-Bodilis
authors: Sylvain
authors: S
authors: Mastrorillo
authors: Frédéric
authors: F
authors: Garabetian
mesh_terms: D001419:Bacteria / Q000235:genetics / Q000378:metabolism; D018407:Bacterial Physiological Phenomena; D001426:Bacterial Proteins / Q000235:genetics / Q000378:metabolism; D018441:Biofilms; D058440:Denitrification; D005602:France; D005618:Fresh Water / Q000737:chemistry*; D064307:Microbiota; D012333:RNA, Messenger / Q000235:genetics / Q000378:metabolism; D060888:Real-Time Polymerase Chain Reaction; D020133:Reverse Transcriptase Polymerase Chain Reaction; D013696:Temperature
chemical_list: D001426:Bacterial Proteins; D012333:RNA, Messenger
keywords: Epilithon; Global change; Periphyton; Potential denitrification; Temperature sensitivity; mRNA