Transcriptional and cellular reprogramming in Anabaena sp. PCC7120 biofilms: implications for stress response.

Cyanobacteria are major components of phototrophic biofilms, driving critical biogeochemical cycles and offering sustainable solutions for agriculture. However, the factors governing their transition from planktonic to sessile lifestyles remain poorly understood. Here, we investigated morphological and transcriptomic differences between planktonic cultures of the filamentous diazotroph Anabaena sp. PCC7120 and their biofilm counterparts. Comparative RNA-sequencing revealed a profound global reprogramming involving 17.7% of the genome, characterized by extensive cell envelope remodelling, a pronounced downregulation of anabolic activity, and the activation of multiple stress-response pathways. Stress assays revealed that nitrogen deficiency and increased salinity markedly enhanced biofilm formation, whereas iron deficiency produced contrasting effects, underscoring how metabolic state shapes the transition to surface-associated growth. These findings establish a direct connection between stress-adaptation pathways and sessile development, providing a framework for harnessing cyanobacterial biofilms in environmental applications.