The dgc2 gene encoding di-guanylate cyclase suppresses both motility and biofilm formation in the filamentous cyanobacterium Leptolyngbya boryana

Colony pattern formations of bacteria with motility manifest complicated morphological self-organization phenomena. Leptolyngbya boryana is the filamentous cyanobacterial species, which has been used as a genetic model organism for studying metabolism including photosynthesis and nitrogen-fixation. Although a widely used type strain (wild type) of this species has not been reported to show any motile activity, we isolated a spontaneous mutant strain which shows active motility (gliding activity) to give rise to complicated colony patters, including comet-like wandering clusters and disk-like rotating vortices on solid media. Whole-genome resequencing identified multiple mutations on the genome in the mutant strain. We confirmed that inactivation of a candidate gene, dgc2 ( LBDG_02920 ), in the wild type background was sufficient to give rise to motility and the morphological colony patterns. This gene encodes a protein, containing the GGDEF motif, which is conserved at the catalytic domain of diguanylate cyclase (DGC). Although DGC has been reported to be involved in biofilm formation, the mutant strain lacking dgc2 significantly facilitated biofilm formation, suggesting a role of DGC for suppressing both gliding motility and biofilm formation. Thus, L. boryana provides an excellent genetic model to study dynamic colony pattern formation, and novel insight on a role of c-di-GMP for biofilm formation. Importance Self-propelled bacteria often show complicated collective behaviors, such as the formation of dense moving clusters, which is exemplified by wandering comet-like and rotating disk-like colonies, while molecular details of forming such structures remain limited. We found that a strain deficient in the diguanylate cyclase gene dgc2 in the filamentous cyanobacterium L. boryana induces motility, complex and dynamic colony pattern formation including the comet-like and disk-like clusters. While c-di-GMP has been reported to activate biofilm formation in some bacterial species, disruption of the dgc2 gene unexpectedly enhanced it, providing a novel role for c-di-GMP regulatory system in both colony pattern formation and biofilm formation.