GGDEF and EAL domains inversely regulate cyclic di-GMP levels and transition from sessility to motility

Cyclic nucleotides represent second messenger molecules in all kingdoms of life. In bacteria, mass sequencing of genomes detected the highly abundant protein domains GGDEF and EAL. We show here that the GGDEF and EAL domains are involved in the turnover of cyclic-di-GMP (c-di-GMP) in vivo whereby the GGDEF domain stimulates c-di-GMP production and the EAL domain c-di-GMP degradation. Thus, most probably, GGDEF domains function as c-di-GMP cyclase and EAL domains as phosphdiesterase. We further show that, in the pathogenic organism Salmonella enterica serovar Typhimurium, the nosocomial pathogen Pseudomonas aeruginosa and the commensal species Escherichia coli, GGDEF and EAL domains mediate similar phenotypic changes related to the transition between sessility and motility. Thus, the data suggest that c-di-GMP is a novel global second messenger in bacteria the metabolism of which is controlled by GGDEF and EAL domain proteins.