Repurposing metal-responsive regulators: The FUR family as a regulatory hub for lifestyle adaptation and biofilm architecture in Anabaena sp. PCC 7120.
Cyanobacterial biofilms play a crucial role in maintaining aquatic ecosystem stability. However, the regulatory mechanisms governing the transition from planktonic growth to a sessile state remain poorly characterized. This lifestyle shift entails extensive transcriptional reprogramming. In Anabaena sp. PCC 7120 the three Ferric Uptake Regulator (FUR) paralogs FurA, Zur and PerR play key roles in coordinating this process. Although these proteins are established regulators of metal and redox homeostasis, their contribution to orchestrating multicellular behaviour has yet to be defined. In this study, we combined computational, biochemical, and surface characterization approaches to evaluate the influence of FUR proteins on biofilm architecture and to map the FUR-mediated regulatory network underlying its development. Our results identified Zur as a major regulator of extracellular matrix formation, directly controlling genes involved in carbohydrate metabolism and trehalose biosynthesis (alr1718, alr0894), thereby promoting structural maturation and desiccation tolerance. In contrast, PerR functioned as a developmental gatekeeper, as its deregulation led to elongated cells with impaired septation associated with the misregulation of the septal-junction regulator sjdR and the fatty acid biosynthesis gene lpxC. FurA maintained cellular homeostasis by regulating α-trehalase (all0166), thereby influencing extracellular matrix turnover. Scanning electron microscopy analysis confirmed that FUR deregulation markedly altered biofilm architecture, whereas environmental stressors such as nitrogen deficiency activated compensatory pathways that partially bypassed these regulatory constraints. Together, these findings demonstrate that metal-responsive regulators are repurposed to integrate environmental signals into the control of prokaryotic multicellularity, positioning the FUR family as a central regulatory hub for lifestyle adaptation in Anabaena.