16The gastrointestinal pathogen Vibrio cholerae frequently forms biofilms during its life 17 cycle. Biofilm formation is vital for protection against environmental stresses and is 18 thought to facilitate intestinal colonization. Adaptation to temperature is crucial for V. 19 cholerae survival, as the pathogen is exposed to seasonal temperature variations in 20 the aquatic environment, and temperature fluctuations during host-environment 21 transitions. Here, we show that V. cholerae strains naturally lacking the master biofilm 22 transcriptional regulator HapR are unable to develop colony rugosity at low 23 temperatures. We find that BipA, a ribosome-associated GTPase, accounts for this 24 temperature-dependent control of biofilm formation by repressing translation of the 25 primary biofilm transcriptional activators VpsR and VpsT at low temperatures. In vitro 26 studies demonstrate that low temperatures influence BipA structural conformation and 27 decrease its sensitivity to proteolysis. Proteomic analyses reveal that BipA exerts 28 temperature-dependent control over >200 proteins in V. cholerae involved in a 29 multitude of cell processes, including biofilm assembly. Our study reveals a 30 remarkable new facet of the complex V. cholerae biofilm regulatory cascade and 31suggests that combined transcriptional-translational control could be a common 32 mechanism by which bacteria adapt to environmental flux.A common strategy of bacteria for adaptation and survival to changing environmental 35 conditions is the formation of biofilms: bacterial communities enclosed in an 36 extracellular matrix. Vibrio cholerae, the causative agent of the severe diarrhoeal 37 disease cholera, forms biofilms both in biotic and abiotic surfaces in the aquatic 38 environment that inhabits 1-3 and also in the intestine of the human host 4,5 . The 39 formation of biofilms enhances persistence of V. cholerae, since it provides protection 40 against environmental insults, predators and stress conditions and allows a better 41 access to nutrients 3 . There is some evidence indicating that biofilm-formation capacity 42 is critical for intestinal colonization 5 and biofilms have also been linked to a 43 hyperinfectious phenotype 6 . 44V. cholerae's biofilm is primarily composed of VPS (Vibrio polysaccharide), matrix 45 proteins (RbmA, RbmC and Bap1) and extracellular DNA 7-13 . The genes encoding the 46 activities for the production of VPS, grouped in the vpsI and vpsII clusters, and the 47 genes encoding the RbmA and RbmC matrix proteins, located in the rbm cluster 48 between vpsI and vpsII clusters, form the so-called V. cholerae biofilm-matrix cluster 49 (VcBMC) 7-10 . 50 Biofilm formation inVibrio cholerae is a highly regulated process, controlled by the 51 transcriptional activators VpsR, VpsT and AphA, the transcriptional repressors HapR 52 and H-NS, small regulatory RNAs, alternative sigma factors (RpoS, RpoN and RpoE), 53 and small nucleotide signalling (c-di-GMP, cAMP, ppGpp). Specific environmental 54 signals such as changes...