title: Evidence for polyploidy in the globally important diazotroph Trichodesmium.
abstract: Polyploidy is a well-described trait in some prokaryotic organisms; however, it is unusual in marine microbes from oligotrophic environments, which typically display a tendency towards genome streamlining. The biogeochemically significant diazotrophic cyanobacterium Trichodesmium is a potential exception. With a relatively large genome and a comparatively high proportion of non-protein-coding DNA, Trichodesmium appears to allocate relatively more resources to genetic material than closely related organisms and microbes within the same environment. Through simultaneous analysis of gene abundance and direct cell counts, we show for the first time that Trichodesmium spp. can also be highly polyploid, containing as many as 100 genome copies per cell in field-collected samples and >600 copies per cell in laboratory cultures. These findings have implications for the widespread use of the abundance of the nifH gene (encoding a subunit of the N2-fixing enzyme nitrogenase) as an approach for quantifying the abundance and distribution of marine diazotrophs. Moreover, polyploidy may combine with the unusual genomic characteristics of this genus both in reflecting evolutionary dynamics and influencing phenotypic plasticity and ecological resilience.
authors: Ocean and Earth Science, University of Southampton, National Oceanography Centre Southampton, Southampton SO14 3ZH, UK.
authors: Elizabeth C
authors: EC
authors: Sargent
authors: Ocean and Earth Science, University of Southampton, National Oceanography Centre Southampton, Southampton SO14 3ZH, UK.
authors: Andrew
authors: A
authors: Hitchcock
authors: Ocean and Earth Science, University of Southampton, National Oceanography Centre Southampton, Southampton SO14 3ZH, UK.
authors: S Andreas
authors: SA
authors: Johansson
authors: Department of Biology, Life Science Centre, Dalhousie University, 1355 Oxford Street, Halifax, NS B3H 4R2, Canada.
authors: Rebecca
authors: R
authors: Langlois
authors: Ocean and Earth Science, University of Southampton, National Oceanography Centre Southampton, Southampton SO14 3ZH, UK.
authors: C Mark
authors: CM
authors: Moore
authors: Department of Biology, Life Science Centre, Dalhousie University, 1355 Oxford Street, Halifax, NS B3H 4R2, Canada.
authors: Julie
authors: J
authors: LaRoche
authors: Ocean Biogeochemistry and Ecosystems, National Oceanography Centre Southampton, Southampton SO14 3ZH, UK.
authors: Alex J
authors: AJ
authors: Poulton
authors: Ocean and Earth Science, University of Southampton, National Oceanography Centre Southampton, Southampton SO14 3ZH, UK.
authors: Thomas S
authors: TS
authors: Bibby
keywords: 
            Trichodesmium
          ; 
            nifH
          ; cyanobacteria; diazotroph; nitrogenase; polyploidy