title: Detection and phylogenetic analysis of the membrane-bound nitrate reductase (Nar) in pure cultures and microbial communities from deep-sea hydrothermal vents.
abstract: Over the past few years the relevance of nitrate respiration in microorganisms from deep-sea hydrothermal vents has become evident. In this study, we surveyed the membrane-bound nitrate reductase (Nar) encoding gene in three different deep-sea vent microbial communities from the East Pacific Rise and the Mid-Atlantic Ridge. Additionally, we tested pure cultures of vent strains for their ability to reduce nitrate and for the presence of the NarG-encoding gene in their genomes. By using the narG gene as a diagnostic marker for nitrate-reducing bacteria, we showed that nitrate reductases related to Gammaproteobacteria of the genus Marinobacter were numerically prevalent in the clone libraries derived from a black smoker and a diffuse flow vent. In contrast, NarG sequences retrieved from a community of filamentous bacteria located about 50 cm above a diffuse flow vent revealed the presence of a yet to be identified group of enzymes. 16S rRNA gene-inferred community compositions, in accordance with previous studies, showed a shift from Alpha- and Gammaproteobacteria to Epsilonproteobacteria as the vent fluids become warmer and more reducing. Based on these findings, we argue that Nar-catalyzed nitrate reduction is likely relevant in temperate and less reducing environments where Alpha- and Gammaproteobacteria are more abundant and where nitrate concentrations reflect that of background deep seawater.
authors.affiliation: Department of Biochemistry and Microbiology, Rutgers University, New Brunswick, NJ, USA; Institute of Marine and Coastal Sciences, Rutgers University, New Brunswick, NJ, USA.
authors.forename: Ileana
authors.initials: I
authors.lastname: Pérez-Rodríguez
authors.forename: Kenneth A
authors.initials: KA
authors.lastname: Bohnert
authors.forename: Mariola
authors.initials: M
authors.lastname: Cuebas
authors.forename: Ramaydalis
authors.initials: R
authors.lastname: Keddis
authors.forename: Costantino
authors.initials: C
authors.lastname: Vetriani
mesh_terms: D001419:Bacteria / Q000145:classification / Q000235:genetics / Q000302:isolation & purification; D044822:Biodiversity; D020565:Epsilonproteobacteria / Q000145:classification / Q000235:genetics / Q000302:isolation & purification; D020563:Gammaproteobacteria / Q000235:genetics / Q000302:isolation & purification; D020459:Genes, rRNA; D060086:Hydrothermal Vents / Q000382:microbiology*; D050901:Nitrate Reductase / Q000145:classification / Q000235:genetics*; D010802:Phylogeny; D020560:Proteobacteria / Q000145:classification* / Q000235:genetics / Q000302:isolation & purification; D012336:RNA, Ribosomal, 16S / Q000235:genetics
chemical_list: D012336:RNA, Ribosomal, 16S; D050901:Nitrate Reductase
keywords: anaerobic respiration; bacteria; deep-sea; hydrothermal fluids; nitrate reduction; nitrogen cycle