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PLoS One. 2015 Jun 23;10(6):e0128912. doi: 10.1371/journal.pone.0128912. eCollection 2015.

Widespread Distribution and Expression of Gamma A (UMB), an Uncultured, Diazotrophic, γ-Proteobacterial nifH Phylotype.

Author information

1
Department of Oceanography, Dalhousie University, Halifax, NS, Canada.
2
The University of Warwick, Coventry, United Kingdom.
3
Environmental Earth System Science, Stanford University, Stanford, California, United States of America.
4
Faculty of Fisheries, Nagasaki University, Nagasaki, Japan.

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.

PMID:
26103055
PMCID:
PMC4477881
DOI:
10.1371/journal.pone.0128912
[Indexed for MEDLINE]
Free PMC Article

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