Abstract Cyclic-di-GMP signaling is used by many bacteria to control biofilm formation. As biofilm formation is an important survival strategy for many bacteria, the synthesis and degradation of cyclic-di-GMP is tightly regulated by enzymes containing domains with conserved GGDEF and EAL sequence motifs, respectively. In this report we characterize a protein with both cyclase and phosphodiesterase activities and demonstrate that it contributes to secretion of the extracellularpolysaccharide matrix, an important step in early biofilm formation.