An operon for a putative ATP-binding cassette transport system involved in acetoin utilization of Bacillus subtilis

The ytrABCDEF operon of Bacillus subtilis was deduced to encode a putative ATP-binding cassette (ABC) transport system. YtrB and YtrE could be the ABC subunits, and YtrC and YtrD are highly hydrophobic and could form a channel through the cell membrane, while YtrF could be a periplasmic lipoprotein for substrate binding. Expression of the operon was examined in cells grown in a minimal medium. The results indicate that the expression was induced only early in the stationary phase. The six ytr genes form a single operon, transcribed from a putative sigma(A)-dependent promoter present upstream of ytrA. YtrA, which possesses a helix-turn-helix motif of the GntR family, acts probably as a repressor and regulates its own transcription. Inactivation of the operon led to a decrease in maximum cell yield and less-efficient sporulation, suggesting its involvement in the growth in stationary phase and sporulation. It is known that B. subtilis produces acetoin as an external carbon storage compound and then reuses it later during stationary phase and sporulation. When either the entire ytr operon or its last gene, ytrF, was inactivated, the production of acetoin was not affected, but the reuse of acetoin became less efficient. We suggest that the Ytr transport system plays a role in acetoin utilization during stationary phase and sporulation.