An operon for a putative ATP-binding cassette transport system involved inacetoin 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 channe l 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 o f ytrA. YtrA, which possesses a helix-turn-helix. motif of the GntR family, acts probably as a repressor and regulates its own transcription. Inactiva tion of the operon led to a decrease in maximum cell yield and less-efficie nt sporulation, suggesting its involvement in the growth in stationary phas e and sporulation. It is known that B. subtilis produces acetoin as an exte rnal carbon storage compound and then reuses it later during stationary pha se and sporulation, When either the entire ytr operon or its last gene, ytr F, was inactivated, the production of acetoin was not affected, but the reu se of acetoin became less efficient. We suggest that the Ytr transport syst em plays a role in acetoin utilization during stationary phase and sporulat ion.