The availability of multiple bacterial genome sequences has led to the discovery of several conserved domains of proteins. Recently, GGDEF and EAL domains have been described as domains responsible for the synthesis and degradation of c-di-GMP, a second messenger in bacteria. c-di-GMP has been involved in cellulose production and identified as a global regulator of several processes such as biofilm formation, motility and virulence, presumibly through a modification of the cell surface properties.