Serves as a specificity factor required for RNase E-mediated decay of the small global regulatory RNAs CsrB and CsrC, it is probably not a nuclease. Nor does its activity involve c-di-GMP, despite its domain composition. Positively modulates motility gene expression, is also required for curli expression. Expressed at low levels at both 28 and 37 degrees Celsius. Removal of the transmembrane regions (residues 1-156) has no effect on csrB translation, however removal of either the HAMP-like region, EAL or GGDEF domains obviates the activity of CsrD. Dramatically stabilizes CsrB and CsrC RNAs, small RNAs that sequester the global carbon storage regulator CsrA; also decreased transcription of CsrB/C (PubMed:16980588). Decreased biofilm formation, decreased expression of DgcC, a probable diguanylate cyclase and of the curli regulator CsgD. Decreased expression of the curlin subunit CsgB, decreased curli expression at 28 degrees Celsius (PubMed:19332833). Although this protein contains both EAL and GGDEF domains it is unlikely to have either c-di-GMP phosphodiesterase or diguanylate cyclase activities as amino acids known to be important to these activities are not conserved.