|The physiological role of riboflavin transporter and involvement of FMN-riboswitch in its gene expression in Corynebacterium glutamicum.
Appl. Microbiol. Biotechnol. 98: 4159-4168. 2014.
N. Takemoto, Y. Tanaka, M. Inui and H. Yukawa.
|Riboflavin is a precursor of flavin mononucleotide (FMN) and flavin adenine
dinucleotide (FAD), which work as cofactors of numerous enzymes. Understanding
the supply system of these cofactors in bacteria, particularly those used
for industrial production of value added chemicals, is important given
the pivotal role the cofactors play in substrate metabolism. In this work,
we examined the effect of disruption of riboflavin utilization genes on
cell growth, cytoplasmic flavin levels, and expression of riboflavin transporter
in Corynebacterium glutamicum. Disruption of the ribA gene that encodes bifunctional GTP cyclohydrolase II/3,4-dihydroxy-2-butanone 4-phosphate synthase in C. glutamicum suppressed growth in the absence of supplemental riboflavin. The growth
was fully recovered upon supplementation with 1 μM riboflavin, albeit at
reduced intracellular concentrations of FMN and FAD during the log phase.
Concomitant disruption of the ribA and ribM gene that encodes a riboflavin transporter exacerbated supplemental riboflavin requirement from 1 μM to 50 μM. RibM expression in FMN-rich cells was about 100-fold lower than that in FMN-limited cells. Mutations in putative FMN-riboswitch present immediately upstream of the ribM gene abolished the FMN response. This 5′UTR sequence of ribM constitutes a functional FMN-riboswitch in C. glutamicum.