Marine diazotrophic cyanobacteria: Out of the blue

Cyanobacteria are now recognized as the primary nitrogen-fixing (diazotrophic) microorganisms in the oceans as contributing significantly to the biogeochemistry of the global nitrogen cycle. The evolution of a remarkable range of morphologies and metabolic capacities has led to a behavioural versatility that helps them to proliferate and combat nutrient limitations in oceanic ecosystems. Advancement in community gene, genome and metagenome analyses of marine microbial communities will further advance functional interpretations and biotechnological uses. In this review we highlight the diversity, adaptation and function of cyanobacteria in the ocean.