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

TY - JOUR

T1 - N-fixation and related O2 constraints on model marine diazotroph Pseudomonas stutzeri BAL361

AU - Paerl, Ryan William

AU - Hansen, Tobias N. G.

AU - Henriksen, Nathalie N. S. E.

AU - Olesen, Asmus K.

AU - Riemann, Lasse

PY - 2018

Y1 - 2018

N2 - 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.

AB - 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.

U2 - 10.3354/ame01867

DO - 10.3354/ame01867

M3 - Journal article

SN - 0948-3055

VL - 81

SP - 125

EP - 136

JO - Aquatic Microbial Ecology

JF - Aquatic Microbial Ecology

IS - 2

ER -