Microorganisms and Habitats

Diverse prokaryotic taxa capable of N2 fixation are found across the many habitats and ecosystems of the oceans. Although variable in the magnitude of rates, microbial diversity and taxonomic composition of species, nif genes have been detected in samples ranging from surface waters to the depths of the sea, in sediments, hydrothermal vents, coral reefs, microbial mats in shallow lagoons and on surfaces, even in habitats with low or undetectable rates of N2 fixation. Marine N2-fixing microorganisms include various cyanobacteria, phototrophic Bacteria (proteobacteria), heterotrophic or photoheterotrophic Bacteria (proteobacteria) and some Archaea. Although Archaea are abundant in the oceans and seafloor, probably the least is known about their physiology including potential for N2 fixation.