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 (N₂ fixation), have adapted to thrive in phosphate (P_i)-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_i limitation, including detecting P_i availability, utilising high-affinity P_i transporters, and hydrolyzing dissolved organic phosphorus (DOP) with various enzymes. This review synthesises current knowledge regarding how cyanobacteria adapt to P_i 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_i scarcity and highlight the need for further research into their molecular adaptive strategies. Adaptation to P_i limitation is often intertwined with the broader response of cyanobacteria to multiple limitations and stresses. This underscores the importance of understanding P_i adaptation to assess the ecological resilience of these crucial microorganisms in dynamic environments, particularly in the context of global climate change.