Current model of the regulatory network controlling the expression of extracellular matrix components required for biofilm formation in Salmonella. The curli subunits CsgA and CsgB are encoded by csgBA, which is positively regulated by the global regulator CsgD . CsgD also activates cellulose production through the expression of AdrA, a member of the GGDEF protein family, which is involved in the activation of cellulose synthesis . Recently, in S. Enterica serovar Entiritidis a large secreted protein, called BapA, has been discovered. BapA was shown to be required for pellicle formation at the air-liquid interface and its expression was demonstrated to be coordinated with that of genes encoding curli and cellulose via CsgD .