Adaptive Responses of Cyanobacteria to Phosphate Limitation: A Focus on Marine Diazotrophs

Phosphorus is an essential component of numerous macromolecules and is vital for life. Its availability significantly influences primary production, particularly in oligotrophic environments. Marine diazotrophic cyanobacteria, which play key roles in biogeochemical cycles through nitrogen fixation (N fixation), have adapted to thrive in phosphate (P)-poor areas. However, the molecular mechanisms that facilitate their adaptation to such conditions remain incompletely understood. Bacteria have evolved various strategies to cope with P limitation, including detecting P availability, utilising high-affinity P transporters, and hydrolyzing dissolved organic phosphorus (DOP) with various enzymes. This review synthesises current knowledge regarding how cyanobacteria adapt to P scarcity, with particular emphasis on subtropical marine free-living diazotrophs and their ability to utilise diverse DOP molecules. Omics approaches, such as (meta)genomics and (meta)transcriptomics, reveal the resilience of marine diazotrophs in the face of P scarcity and highlight the need for further research into their molecular adaptive strategies. Adaptation to P limitation is often intertwined with the broader response of cyanobacteria to multiple limitations and stresses. This underscores the importance of understanding P adaptation to assess the ecological resilience of these crucial microorganisms in dynamic environments, particularly in the context of global climate change.