36Altering membrane protein and lipid composition is an important strategy for maintaining 37 membrane integrity during environmental stress. Many bacterial small RNAs (sRNAs) 38 control membrane protein production, but sRNA-mediated regulation of membrane fatty 39 acid composition is less understood. The sRNA RydC was previously shown to stabilize 40 cfa (cyclopropane fatty acid synthase) mRNA, resulting in higher levels of cyclopropane 41 fatty acids in the cell membrane. Here, we report that three additional sRNAs, ArrS, 42CpxQ, and GadF also regulate cfa post-transcriptionally. RydC, ArrS, and GadF act 43 through masking an RNase E cleavage site in the cfa mRNA 5' untranslated region 44 (UTR), and all three sRNAs post-transcriptionally activate cfa. In contrast, CpxQ binds to 45 a different site in the cfa mRNA 5' UTR and represses cfa. Alteration of membrane lipid 46 composition is a key mechanism for bacteria to survive low pH environments, and we 47show that cfa translation increases in an sRNA-dependent manner when cells are 48 subjected to mild acid stress. This work suggests an important role for sRNAs in the acid 49 stress response through regulation of cfa mRNA. 50 51