PT  - JOURNAL ARTICLE
AU  - Colleen M. Bianco
AU  - Carin K. Vanderpool
TI  - Multiple Small RNAs Alter Membrane Lipid Composition via Post-Transcriptional Regulation of Cyclopropane Fatty Acid Synthase
AID  - 10.1101/271551
DP  - 2018 Jan 01
TA  - bioRxiv
PG  - 271551
4099  - http://biorxiv.org/content/early/2018/02/25/271551.short
4100  - http://biorxiv.org/content/early/2018/02/25/271551.full
AB  - Microbial membranes are the first line of defense against environmental stress as well as the site of many metabolic processes. As such, maintenance of membrane integrity and homeostasis is key to cell survival. Altering membrane protein and lipid composition is an important strategy for maintaining membrane integrity in response to many environmental stresses. There are now numerous examples of small RNA (sRNA)-mediated regulation of membrane protein production, but less is known about how sRNAs regulate the types and relative proportions of different fatty acids in the membrane. The only sRNA known to regulate membrane fatty acid composition is RydC, which stabilizes cfa mRNA, encoding cyclopropane fatty acid (CFA) synthase, resulting in increased production of the synthase and higher levels of cyclopropane fatty acids (CFAs) in the cell membrane. Here, we report that three additional sRNAs, ArrS, CpxQ, and GadF also alter cfa translation and thus the amount of CFAs in cell membranes. RydC, ArrS, and GadF bind at sites that overlap a known RNase E cleavage site in the cfa mRNA 5′-untranslated region (UTR), resulting in increased cfa mRNA stability and translation. In contrast, CpxQ binds to a different site in the cfa mRNA 5′-UTR, and acts to reduce cfa translation. The physiological role of CFAs in membrane lipids is poorly understood, but CFAs have been shown to promote bacterial resistance to acid stress. We show that cfa translation increases in an sRNA-dependent manner when cells are subjected to mild acid stress. RydC is necessary for an increase in cfa translation at pH 5.0 and a rydC mutant is more sensitive to acid shock than the rydC+ strain. Alteration of membrane lipid composition is a key mechanism for bacterial responses to many environmental stresses, including acid stress. This work suggests an important role for sRNAs in these responses through their regulation of cfa mRNA.