PANDA, MANIOC & ANITA

PArticles as Niches for non-cyanobacterial DiAzotrophs

Project funding

Project overview

Nitrogen fixation has been classically attributed to autotrophic cyanobacteria. In the past couple of decades, sequencing of marker genes has demonstrated that non-cyanobacterial diazotrophs (NCDs) including bacteria and archaea- dominate in the coastal systems. NCDs are thus suspected to impact global nitrogen cycling decisively, yet no study has been able to show their specific nitrogen fixation activity. These measurements have been elusive due to the coexistence of cyanobacterial diazotrophs and NCDs, the unknown niches and lifestyles of NCDs, as well as their immense phylogenetic diversity which hampers the development of taxa-specific assays. Previous studies have suggested that NCDs need low oxygen loci to develop, which in the fully oxygenated ocean water column can only be found in particle environments. In PANDA, MANIOC and ANITA we propose to measure NCD-specific nitrogen fixation rates in particles using an original combination of immunofluorescence, microtomy, advanced microscopy and single-cell mass spectrometry techniques.

Fig. 1: V. diazotrophicus cells incubated (a-c) with or (d-f) without particles. Left images correspond to DAPI staining, right images represent nitrogenase enzyme immunostaining, and center images are the merger of the two colors. We observe that V. diazotrophicus accumulates around particles (a-c), which presumably provide them with a source or organic carbon and energy to fuel the metabolically expensive process of N2 fixation. In the absence of particles (d-f), cells are sparsely distributed and do not express nitrogenase.

Objectives and approach

PANDA will apply an innovative combination of microscopy, genomics and isotopic methods to visualize NCDs colonizing particles and measure N2 fixation activity at the single-cell level. Our results will provide the first NCD-specific N2 fixation measurements in coastal ecosystems.

1) Develop a method capable of measuring particle-attached N2 fixation by NCDs

2) To apply the method to a coastal ecosystem and evaluate their contribution to nitrogen inputs

Bridges members involved

Arthur Coët

Elena Cerdán

Christian Furbo Reeder

Project collaborators

Kendra Turk-Kubo (UCSC, USA)

Matt Mills (Stanford, USA)

Angela Vogts (IOW, Germany)

Daniel Borschneck (CEREGE, France)

Pierre Ronceray (CINaM, France)

Frédéric Le Moigne (LEMAR, France)

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