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Ethanolamine (EA) is a compound prevalent in the gastrointestinal (GI) tract that can be used as a carbon, nitrogen, and/or energy source. Enterococcus faecalis , a GI commensal and opportunistic pathogen, contains approximately 20 e thanolamine ut ilization ( eut ) genes encoding the necessary regulatory, enzymatic, and structural proteins for this process. Here, using a chemically defined medium, two regulatory factors that affect EA utilization were examined. First, the functional consequences of loss of the small RNA (sRNA) EutX on the efficacy of EA utilization were investigated. One effect observed, as loss of this negative regulator causes an increase in eut gene expression, was a concomitant increase in the number of catabolic b acterial m icro c ompartments (BMCs) formed. However, despite this increase, the growth of the strain was repressed, suggesting that the overall efficacy of EA utilization was negatively affected. Second, utilizing a deletion mutant and a complement, carbon catabolite control protein A (CcpA) was shown to be responsible for the repression of EA utilization in the presence of glucose. A predicted cre site in one of the three EA-inducible promoters, PeutS , was identified as the target of CcpA. However, CcpA was shown to affect the activation of all the promoters indirectly through the two-component system EutV and EutW, whose genes are under the control of the PeutS promoter. Moreover, a bioinformatics analysis of bacteria predicted to contain CcpA and cre sites revealed that a preponderance of BMC-containing operons are likely regulated by carbon catabolite repression (CCR). IMPORTANCE Ethanolamine (EA) is a compound commonly found in the gastrointestinal (GI) tract that can affect the behavior of human pathogens that can sense and utilize it, such as Enterococcus faecalis and Salmonella Therefore, it is important to understand how the genes that govern EA utilization are regulated. In this work, we investigated two regulatory factors that control this process. One factor, a small RNA (sRNA), is shown to be important for generating the right levels of gene expression for maximum efficiency. The second factor, a transcriptional repressor, is important for preventing expression when other preferred sources of energy are available. Furthermore, a global bioinformatics analysis revealed that this second mechanism of transcriptional regulation likely operates on similar genes in related bacteria., (Copyright © 2019 American Society for Microbiology.)

The ethanolamine utilization (eut) locus of Enterococcus faecalis, containing at least 19 genes distributed over four polycistronic messenger RNAs, appears to be regulated by a single adenosyl cobalamine (AdoCbl)-responsive riboswitch. We report that the AdoCbl-binding riboswitch is part of a small, trans-acting RNA, EutX, which additionally contains a dual-hairpin substrate for the RNA binding-response regulator, EutV. In the absence of AdoCbl, EutX uses this structure to sequester EutV. EutV is known to regulate the eut messenger RNAs by binding dual-hairpin structures that overlap terminators and thus prevent transcription termination. In the presence of AdoCbl, EutV cannot bind to EutX and, instead, causes transcriptional read through of multiple eut genes. This work introduces riboswitch-mediated control of protein sequestration as a posttranscriptional mechanism to coordinately regulate gene expression., (Copyright © 2014, American Association for the Advancement of Science.)