Nitrogenase genes in non-cyanobacterial plankton: prevalence, diversity, and regulation in marine waters

TY - JOUR

T1 - Nitrogenase genes in non-cyanobacterial plankton: prevalence, diversity, and regulation in marine waters

AU - Riemann, Lasse

AU - Farnelid, H.

AU - Steward, G.F.

N1 - KEY WORDS: N2 fixation · Nitrogen fixation · Non-Cyanobacteria · nifH · Nitrogenase

PY - 2010

Y1 - 2010

N2 - Marine waters are generally considered to be nitrogen (N) limited and are therefore favourable environments for diazotrophs, i.e. organisms converting atmospheric N2 into ammonium or nitrogen oxides available for growth. In some regions, this import of N supports up to half of the primary productivity. Diazotrophic Cyanobacteria appear to be the major contributors to marine N2 fixation in surface waters, whereas the contribution of heterotrophic or chemoautotrophic diazotrophs to this process is usually regarded inconsequential. Culture-independent studies reveal that non-cyanobacterial diazotrophs are diverse, widely distributed, and actively expressing the nitrogenase gene in marine and estuarine environments. The detection of nifH genes and nifH transcripts, even in N-replete marine waters, suggests that N2 fixation is an ecologically important process throughout the oceans. Because this process is highly sensitive to and inhibited by molecular oxygen (O2), diazotrophy requires efficient scavenging of intracellular O2 or growth in environments with low ambient O2 concentration. Particles with interior low-O2 micro-zones and oceanic oxygen minimum zones are just 2 potential habitats suitable for N2 fixation by non-cyanobacterial diazotrophs. Our ignorance about the regulation of N2 fixation by non-Cyanobacteria in their natural marine environments currently prevents an evaluation of their importance in marine N cycling and budgets. A review of the molecular data on distribution and expression of nifH genes in non-Cyanobacteria suggests that further study of the role of these Bacteria in N cycling at local, regional and global scales is needed.

AB - Marine waters are generally considered to be nitrogen (N) limited and are therefore favourable environments for diazotrophs, i.e. organisms converting atmospheric N2 into ammonium or nitrogen oxides available for growth. In some regions, this import of N supports up to half of the primary productivity. Diazotrophic Cyanobacteria appear to be the major contributors to marine N2 fixation in surface waters, whereas the contribution of heterotrophic or chemoautotrophic diazotrophs to this process is usually regarded inconsequential. Culture-independent studies reveal that non-cyanobacterial diazotrophs are diverse, widely distributed, and actively expressing the nitrogenase gene in marine and estuarine environments. The detection of nifH genes and nifH transcripts, even in N-replete marine waters, suggests that N2 fixation is an ecologically important process throughout the oceans. Because this process is highly sensitive to and inhibited by molecular oxygen (O2), diazotrophy requires efficient scavenging of intracellular O2 or growth in environments with low ambient O2 concentration. Particles with interior low-O2 micro-zones and oceanic oxygen minimum zones are just 2 potential habitats suitable for N2 fixation by non-cyanobacterial diazotrophs. Our ignorance about the regulation of N2 fixation by non-Cyanobacteria in their natural marine environments currently prevents an evaluation of their importance in marine N cycling and budgets. A review of the molecular data on distribution and expression of nifH genes in non-Cyanobacteria suggests that further study of the role of these Bacteria in N cycling at local, regional and global scales is needed.

U2 - 10.3354/ame01431

DO - 10.3354/ame01431

M3 - Journal article

SN - 0948-3055

VL - 61

SP - 235

EP - 247

JO - Aquatic Microbial Ecology

JF - Aquatic Microbial Ecology

IS - 3

ER -