A novel transporter ThuT, couples the biosynthesis and secretion of thuringiensin

Abstract

Thuringiensin is a thermostable nucleoside metabolite produced by Bacillus thuringiensis and has insecticidal activity against various pests. The synthesis cluster of thuringiensin was cloned and the biosynthesis pathway deduced and clarified in a previous study. ThuE catalyzes phosphorylation from precursor C to thuringiensin in the final step of thuringiensin maturation. However, the transport mechanism of thuringiensin remains unclear. Here, we identify a novel predicted MFS transporter named ThuT (thuringiensin transporter) which is necessary for the biosynthesis and secretion of thuringiensin. A thuT gene deletion resulted in a massive loss of thuringiensin in the extracellular space and a small accumulation in the intracellular space, implying its role in the transport of thuringiensin. The overall abundance of thuringiensin was significantly reduced, while the accumulation of precursor C in the thuT mutant suggests its role in thuringiensin biosynthesis. Further proteinprotein interaction analysis demonstrated that ThuT forms a complex with ThuE, which suggests the mechanism by which ThuT participates in thuringiensin maturation. We have identified the first transporter of thuringiensin and propose that the ThuT-ThuE complex could couple the maturation and transport of thuringiensin to avoid thuringiensin accumulation. A novel high-efficiency model coupling the synthesis and secretion of antibiotics has been revealed in B.thuringiensis.