Transcription of cis Antisense Small RNA MtlS in Vibrio cholerae Is Regulated by Transcription of Its Target Gene, mtlA

Vibrio cholerae, the facultative pathogen responsible for cholera disease, continues to pose a global health burden. Its persistence can be attributed to a flexible genetic tool kit that allows for adaptation to different environments with distinct carbon sources, including the six-carbon sugar alcohol mannitol. V. cholerae takes up mannitol through the transporter protein MtlA, whose production is downregulated at the posttranscriptional level by MtlS, a cis antisense small RNA (sRNA) whose promoter lies within the mtlA open reading frame. Though it is known that mtlS expression is robust under growth conditions lacking mannitol, it has remained elusive as to what factors govern the steady-state levels of MtlS. Here, we show that manipulating mtlA transcription is sufficient to drive inverse changes in MtlS levels, likely through transcriptional interference. This work has uncovered a cis-acting sRNA whose expression pattern is predominantly controlled by transcription of the sRNA’s target gene. IMPORTANCE Vibrio cholerae is a bacterial pathogen that relies on genetic tools, such as regulatory RNAs, to adapt to changing extracellular conditions. While many studies have focused on how these regulatory RNAs function, fewer have focused on how they are themselves modulated. V. cholerae expresses the noncoding RNA MtlS, which can regulate mannitol transport and use, and here we demonstrate that MtlS levels are controlled by the level of transcription occurring in the antisense direction. Our findings provide a model of regulation describing how bacteria like V. cholerae can modulate the levels of an important regulatory RNA. Our work contributes to knowledge of how bacteria deploy regulatory RNAs as an adaptive mechanism to buffer against environmental flux.