N-fixation and related O2 constraints on model marine diazotroph Pseudomonas stutzeri BAL361

Abstract

AME Aquatic Microbial Ecology Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsSpecials AME 81:125-136 (2018) - DOI: https://doi.org/10.3354/ame01867 N-fixation and related O2 constraints on model marine diazotroph Pseudomonas stutzeri BAL361 Ryan W. Paerl*, Tobias N. G. Hansen, Nathalie N. S. E. Henriksen, Asmus K. Olesen, Lasse Riemann Marine Biological Section, University of Copenhagen, 3000 Helsingør, Denmark *Corresponding author: rpaerl@ncsu.edu ABSTRACT: Marine non-cyanobacterial diazotrophs are widespread in the ocean and can be the dominant nitrogen (N) fixers in certain regions. Lagging behind distribution and diversity data for these diazotrophs is a fundamental understanding of their physiologies—particularly in regards to dealing with oxygen, a potential inhibitor of N-fixation present in most of the ocean. To address this constraint, we conducted multiple experiments with Pseudomonas stutzeri BAL361, a model marine planktonic non-cyanobacterial diazotroph previously isolated from the Baltic Sea. Here, we confirm that BAL361 uses nitrogenase to convert N2 gas into biomass via N-fixation, reaching N-fixation rates upwards of 0.046 fmol N cell-1 h-1. Planktonic BAL361 cells exhibited nitrogenase activity at ~54 µM O2 or less—an O2 threshold notably lower than that recently reported (~160 µM O2) in experiments with BAL361 where large aggregates were observed. Provision of hydrophobic or hydrophilic particles or surfaces, used previously to stimulate N-fixation by aerobic natural communities, did not enhance N-fixation by aerobic BAL361 cultures. We empirically show that bulk N-fixation under aerobic conditions by BAL361 alone is possible by aggregation; however, it remains elusive how low numbers of solitary planktonic BAL361 cells in nature accomplish this same feat. Our findings draw new attention to the possibility that nutrient-rich conditions (including N-rich conditions) may be key to ultimately enable diazotrophs like BAL361 to overcome the ‘O2 problem’ and perform N-fixation via microoxic zones within aerobic marine bulk waters. KEY WORDS: Diazotrophs · N-fixation · Pseudomonas · Oxygen · Marine particles Full text in pdf format Supplementary material PreviousNextCite this article as: Paerl RW, Hansen TNG, Henriksen NNSE, Olesen AK, Riemann L (2018) N-fixation and related O2 constraints on model marine diazotroph Pseudomonas stutzeri BAL361. Aquat Microb Ecol 81:125-136. https://doi.org/10.3354/ame01867 Export citation RSS - Facebook - Tweet - linkedIn Cited by Published in AME Vol. 81, No. 2. Online publication date: March 21, 2018 Print ISSN: 0948-3055; Online ISSN: 1616-1564 Copyright © 2018 Inter-Research.