Abstract
BackgroundRiboflavin is the precursor of important redox cofactors such as flavin mononucleotide (FMN) and flavin adenine dinucleotide, required for several biological processes. Vibrio cholerae, a pathogenic bacterium responsible for the cholera disease, possesses the ability to biosynthesize de novo as well as to uptake riboflavin through the riboflavin biosynthetic pathway (RBP) and the RibN importer, respectively. The intra-organism relationship between riboflavin biosynthesis and uptake functions has not been studied.ResultsThis work determined the transcriptional organization of RBP genes and ribN in V. cholerae through reverse transcription polymerase chain reaction and analyzed their expression when growing with or without extracellular riboflavin using real time PCR. The RBP is organized in three transcriptional units, the major one containing ribD, ribE, ribA and ribH together with genes involved in functions not directly related to riboflavin biosynthesis such as nrdR and nusB. In addition, two independent monocistronic units contain ribA2 and ribB, the later conserving a putative FMN riboswitch. The ribN gene is encoded in operon with a gene coding for a predicted outer membrane protein and a gene encoding a protein with a glutaredoxin domain. Regulation analysis showed that among these transcriptional units, only ribB is negatively regulated by riboflavin and that its repression depends on the RibN riboflavin importer. Moreover, external riboflavin highly induced ribB transcription in a ΔribN strain. Also, a genomic database search found a negative correlation between the presence of nrdR and nusB and the FMN riboswitch in bacterial RBP operons.ConclusionsGrowing in the presence of riboflavin downregulates only a single element among the transcriptional units of riboflavin supply pathways. Thus, endogenous riboflavin biosynthesis seems to be negatively regulated by extracellular riboflavin through its specific effect on transcription of ribB in V. cholerae.
Highlights
Riboflavin is the precursor of important redox cofactors such as flavin mononucleotide (FMN) and flavin adenine dinucleotide, required for several biological processes
To gain insights into the cues governing the interrelation between riboflavin biosynthesis and transport, we investigated the effect of extracellular riboflavin on the expression of the transcriptional units encoding the riboflavin supply pathways
Transcriptional organization of riboflavin supply pathways in V. cholerae We searched the genome of V. cholerae N16961 in the Kyoto encyclopedia of genes and genomes (KEGG) [34] for riboflavin biosynthetic pathway (RBP) genes and ribN
Summary
Riboflavin is the precursor of important redox cofactors such as flavin mononucleotide (FMN) and flavin adenine dinucleotide, required for several biological processes. RBP and riboflavin importer genes conserve the FMN riboswitch [9, 12, 15, 16, 23,24,25]. This is a genetic element encoded in RNA leader regions, which downregulates transcription and/or translation by adopting alternative expression-permissive or expression-repressive secondary structures in response to FMN binding [25, 26]. Many riboflavin supply genes seem to be regulated in response to intracellular flavin levels
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
