TY - JOUR
T1 - Genomics and ecophysiology of heterotrophic nitrogen fixing bacteria isolated from estuarine surface water
AU - Bentzon-Tilia, Mikkel
AU - Severin, Ina
AU - Hansen, Lars H.
AU - Riemann, Lasse
N1 - This is an open-access article distributed under the terms of the Creative Commons Attribution-Noncommercial-ShareAlike 3.0 Unported license, which permits unrestricted noncommercial use, distribution, and reproduction in any medium, provided the original author and source are credited.
PY - 2015
Y1 - 2015
N2 - The ability to reduce atmospheric nitrogen (N2) to ammonia, known as N2 fixation, is a widely distributed trait
among prokaryotes that accounts for an essential input of new N to a multitude of environments. Nitrogenase reductase gene
(nifH) composition suggests that putative N2-fixing heterotrophic organisms are widespread in marine bacterioplankton, but
their autecology and ecological significance are unknown. Here, we report genomic and ecophysiology data in relation to N2 fixation
by three environmentally relevant heterotrophic bacteria isolated from Baltic Sea surface water: Pseudomonas stutzeri
strain BAL361 and Raoultella ornithinolytica strain BAL286, which are gammaproteobacteria, and Rhodopseudomonas palustris
strain BAL398, an alphaproteobacterium. Genome sequencing revealed that all were metabolically versatile and that the gene
clusters encoding the N2 fixation complex varied in length and complexity between isolates. All three isolates could sustain
growth by N2 fixation in the absence of reactive N, and this fixation was stimulated by low concentrations of oxygen in all three
organisms (≈4 to 40 μmol O2 liter-1). P. stutzeri BAL361 did, however, fix N at up to 165 μmol O2 liter-1, presumably accommodated
through aggregate formation. Glucose stimulated N2 fixation in general, and reactive N repressed N2 fixation, except
that ammonium (NH4
) stimulated N2 fixation in R. palustris BAL398, indicating the use of nitrogenase as an electron sink. The
lack of correlations between nitrogenase reductase gene expression and ethylene (C2H4) production indicated tight
posttranscriptional-level control. The N2 fixation rates obtained suggested that, given the right conditions, these heterotrophic
diazotrophs could contribute significantly to in situ rates.
IMP
AB - The ability to reduce atmospheric nitrogen (N2) to ammonia, known as N2 fixation, is a widely distributed trait
among prokaryotes that accounts for an essential input of new N to a multitude of environments. Nitrogenase reductase gene
(nifH) composition suggests that putative N2-fixing heterotrophic organisms are widespread in marine bacterioplankton, but
their autecology and ecological significance are unknown. Here, we report genomic and ecophysiology data in relation to N2 fixation
by three environmentally relevant heterotrophic bacteria isolated from Baltic Sea surface water: Pseudomonas stutzeri
strain BAL361 and Raoultella ornithinolytica strain BAL286, which are gammaproteobacteria, and Rhodopseudomonas palustris
strain BAL398, an alphaproteobacterium. Genome sequencing revealed that all were metabolically versatile and that the gene
clusters encoding the N2 fixation complex varied in length and complexity between isolates. All three isolates could sustain
growth by N2 fixation in the absence of reactive N, and this fixation was stimulated by low concentrations of oxygen in all three
organisms (≈4 to 40 μmol O2 liter-1). P. stutzeri BAL361 did, however, fix N at up to 165 μmol O2 liter-1, presumably accommodated
through aggregate formation. Glucose stimulated N2 fixation in general, and reactive N repressed N2 fixation, except
that ammonium (NH4
) stimulated N2 fixation in R. palustris BAL398, indicating the use of nitrogenase as an electron sink. The
lack of correlations between nitrogenase reductase gene expression and ethylene (C2H4) production indicated tight
posttranscriptional-level control. The N2 fixation rates obtained suggested that, given the right conditions, these heterotrophic
diazotrophs could contribute significantly to in situ rates.
IMP
M3 - Journal article
SN - 2150-7511
VL - 6
JO - mBio (Online)
JF - mBio (Online)
IS - 4
M1 - e00929-15
ER -