Post‐transcriptional activation of a diguanylate cyclase by quorum sensing small RNAs promotes biofilm formation in V ibrio cholerae

Summary Biofilms promote attachment of V ibrio cholerae in aquatic ecosystems and aid in transmission. Intracellular c‐di‐ GMP levels that control biofilm development positively correlate with expression of Q rr sRNAs , which are transcribed when quorum sensing ( QS ) autoinducer levels are low. The Q rr sRNAs base‐pair with and repress translation of hapR encoding the QS ‘master regulator’, hence increased c‐di‐ GMP and biofilm development at low density were believed to be solely a consequence of Q rr/ hapR pairing. We show that Q rr sRNAs also base‐pair with and activate translation of the mRNA of a diguanylate cyclase ( DGC ), V ca0939; relieving an inhibitory structure in vca0939 that occludes the ribosome binding site. A nucleotide substitution in vca0939 disrupted sRNA / mRNA base‐pairing and prevented vca0939 translation, while a compensating Q rr sRNA substitution restored pairing and V ca0939 levels. Qrr‐dependent DGC activation led to c‐di‐ GMP accumulation and biofilm development in V . cholerae . This represents the first description of (1) a DGC post‐transcriptionally activated by direct pairing with an H fq‐dependent sRNA , and (2) control of a V . cholerae   QS phenotype, independent of HapR . Thus, direct interactions of the same sRNAs with two mRNAs promote c‐di‐ GMP ‐dependent biofilm formation by complementary mechanisms in V . cholerae ; by negatively regulating HapR , and positively regulating the DGC V ca0939.