title: Widespread Distribution and Expression of Gamma A (UMB), an Uncultured, Diazotrophic, γ-Proteobacterial nifH Phylotype.
abstract: Marine dinitrogen (N2) fixation studies have focused nearly exclusively on cyanobacterial diazotrophs; however γ-proteobacteria are an abundant component of the marine community and have been largely overlooked until recently. Here we present a phylogenetic analysis of all nifH γ-proteobacterial sequences available in public databases and qPCR data of a γ-proteobacterial phylotype, Gamma A (UMB), obtained during several research cruises. Our analysis revealed a complex diversity of diazotrophic γ-proteobacteria. One phylotype in particular, Gamma A, was described in several traditional and quantitative PCR studies. Though several γ-proteobacterial nifH sequences have been described as laboratory contaminants, Gamma A is part of a large cluster of sequences isolated from marine environments and distantly related to the clade of contaminants. Using a TaqMan probe and primer set, Gamma A nifH DNA abundance and expression were analyzed in nearly 1000 samples collected during 15 cruises to the Atlantic and Pacific Oceans. The data showed that Gamma A is an active, cosmopolitan diazotroph found throughout oxygenated, oligotrophic waters reaching maximum abundances of 8 x 104 nifH DNA copies l-1 and 5 x 105 nifH transcript copies l-1. Gamma A nifH transcript abundances were on average 3 fold higher than nifH DNA abundances. The widespread distribution and activity of Gamma A indicate that it has potential to be a globally important N2 fixing organism.
authors.affiliation: Department of Oceanography, Dalhousie University, Halifax, NS, Canada.
authors.forename: Rebecca
authors.initials: R
authors.lastname: Langlois
authors.affiliation: The University of Warwick, Coventry, United Kingdom.
authors.forename: Tobias
authors.initials: T
authors.lastname: Großkopf
authors.affiliation: Environmental Earth System Science, Stanford University, Stanford, California, United States of America.
authors.forename: Matthew
authors.initials: M
authors.lastname: Mills
authors.affiliation: Faculty of Fisheries, Nagasaki University, Nagasaki, Japan.
authors.forename: Shigenobu
authors.initials: S
authors.lastname: Takeda
authors.affiliation: Department of Oceanography, Dalhousie University, Halifax, NS, Canada.
authors.forename: Julie
authors.initials: J
authors.lastname: LaRoche
mesh_terms: D005798:Genes, Bacterial; D016013:Likelihood Functions; D010088:Oxidoreductases / Q000235:genetics*; D010802:Phylogeny; D020560:Proteobacteria / Q000145:classification / Q000235:genetics*; D012333:RNA, Messenger / Q000235:genetics; D020133:Reverse Transcriptase Polymerase Chain Reaction
chemical_list: D012333:RNA, Messenger; D010088:Oxidoreductases; C029130:nitrogenase reductase