Towards the control of biofilm formation in Anabaena (Nostoc) sp. PCC7120: novel insights into the genes involved and their regulation.

Cyanobacteria are major components of biofilms in light-exposed environments, contributing to nutrient cycling, nitrogen fixation and global biogeochemical processes. Although nitrogen-fixing cyanobacteria have been successfully used in biofertilization, the regulatory mechanisms underlying biofilm formation remain poorly understood. In this work, we have identified 183 novel genes in Anabaena sp. PCC7120 potentially associated with exopolysaccharide (EPS) biosynthesis and biofilm formation, unveiling conserved and novel regulatory connections shared with phylogenetically distant bacteria. Anabaena possesses homologues of two-component systems such as XssRS and ColRS from Xanthomonas spp., and AnCrpAB from Methylobacillus, suggesting that these homologues play essential or advantageous roles in biofilm formation across diverse bacterial lineages. Additionally, Anabaena features homologues of several proteins exhibiting the GG-secretion motif typical of small proteins required for biofilm formation in unicellular cyanobacteria. A wide array of biofilm-related genes in Anabaena, including major gene clusters participating in the synthesis and translocation of EPS and key regulatory proteins involved in the control of biofilms in other bacteria are modulated by ferric uptake regulator proteins. These findings link the control of biofilm formation in Anabaena to environmental cues such as metal availability, desiccation and nitrogen levels, providing new insights to improve the use of nitrogen-fixing cyanobacterial biofilms in sustainable agriculture and environmental management.