Problems and promises of assaying the genetic potential for nitrogen fixation in the marine environment

Nitrogen fixation in the sea has attracted the attention of ecologists for decades. Much is known about the habitats in which it occurs and some of the factors that limit N₂ fixation activity in different environments, but we still know little about the organisms that fix nitrogen, and what limits the growth and distribution of these organisms in marine environments. Molecular biology technological developments have provided tools for detecting and characterizing N₂-fixing organisms in the environment. These techniques hold great promise for unraveling the mysteries and paradoxes of N₂ fixation in the sea. In this review, we address the theoretical basis for the use of a molecular approach to N₂ fixation, highlight the strengths and weaknesses of the approach, and provide case studies that demonstrate the potential contribution of molecular biology approaches to studies of N₂ fixation in the sea.Correspondence to: J.P. Zehr.