for suitability as antibacterial drug targets, classified the cobalamin riboswitch as being partially suitable for targeting with antibiotics. As of 2019, cobalamin riboswitches were found in 5174 bacterial species, 7% of which are human pathogens. The development of antibiotics targeting the cobalamin riboswitch is hindered due to the fact that not all cobalamin biosynthetic pathways are regulated by riboswitches, meaning that antibiotics targeting the riboswitch would need to be used in conjunction with additional drugs targeting alternative synthetic pathways in order to be effective. As of 2021, no therapeutics targeting the cobalamin riboswitch are being developed. As biosensors riboswitches are ideally suited to be engineered into biosensors due to their ability to undergo a conformational switch upon binding to specific ligands. These sensors are constructed with a cobalamin riboswitch upstream of a gene encoding for a reporter molecule. The nature of the reporter molecule can vary depending on the desired detection method. For example, the reporter gene can encode for green fluorescent protein (GFP) when fluorescence-based detection methods are desired. In the presence of ligand, the riboswitch undergoes a conformational change which blocks the ribosomal binding site, halting transcription of the reporter gene. In 2010, researchers designed the first riboswitch-based AdoCbl sensor in E. coli. This sensor was also used to detect vitamin B12 biosynthetic precursors such as cobinamide and confirm the involvement of specific genes in cobalamin metabolism. More recently, this sensor was used to screen S. meliloti mutants for their ability to synthesize large quantities of Vitamin B12. Riboswitch sensors can be utilized outside of a cellular environment. For example, a biosensor developed from a Propionibacterium freudenreichii cobalamin riboswitch was used to determine the vitamin B12 concentration in fermented food with high sensitivity. References External links Cis-regulatory RNA elements Riboswitch