Vibrio cholerae
continues to pose a health threat in many developing nations and regions of the world struck by natural disasters. It is a pathogen that rapidly adapts to aquatic environments and the human small intestine. Small regulatory RNAs (sRNAs) may contribute to this adaptability. Specifically, the mannitol operon sRNA (MtlS sRNA; previously designated the IGR7 sRNA) is transcribed antisense to the 5′ untranslated region of the
mtl
operon, encoding the mannitol-specific phosphotransferase system. Mannitol is a six-carbon sugar alcohol that accumulates in the human small intestine, the primary site of
V. cholerae
colonization. To better understand the
V. cholerae
mtl
operon at a molecular level, we investigated
mtlA
expression in the presence of various carbon sources and the role of the MtlS sRNA. We observed that MtlA protein is present only in cells grown on mannitol sugar, whereas MtlS sRNA is expressed during growth on all sugars other than mannitol. In contrast,
mtlA
mRNA is expressed in similar amounts regardless of the carbon source used for bacterial growth. These observations suggest that the regulation of MtlA protein expression is a posttranscriptional event. We further demonstrate that MtlS sRNA overexpression repressed MtlA synthesis without affecting the stability of the messenger and that this process is largely independent of Hfq. We propose a model in which, when carbon sources other than mannitol are present, MtlS sRNA is transcribed, base pairs with the 5′ untranslated region of the
mtlA
mRNA, occluding the ribosome binding site, and inhibits the synthesis of the mannitol-specific phosphotransferase system.
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