The repression of trehalose transport and metabolism in Escherichia coli by high osmolarity is mediated by trehalose-6-phosphate phosphatase.

Trehalose transport and metabolism in Escherichia coli are induced by trehalose in the growth medium but only at low osmolarity. In contrast, synthesis of internal trehalose as an osmoprotectant occurs only at high osmolarity, independent of the carbon source. The synthesis of internal trehalose proceeds via the UDP-glucose-mediated transfer of glucose to glucose-6-phosphate, forming trehalose-6-phosphate, which is then hydrolysed to trehalose. We demonstrate that the inducer for the synthesis of the trehalose transport system as well as of amylotrehalase, the key enzyme in trehalose metabolism at low osmolarity, is trehalose-6-phosphate. We found that the inability to induce these proteins at high osmolarity is primarily due to activity of trehalose-6-phosphate phosphatase, the enzyme responsible for the final step in the synthesis of internal trehalose under these conditions. A gene, otsP, necessary for the synthesis of the biosynthetic trehalose-6-phosphate phosphatase, is located at min 42 closely linked to otsA/B the structural genes for the trehalose-6-phosphate synthase. There is another gene locus near 84 min on the chromosome, that we termed otsR, which is involved in the regulation of otsA/B and possibly otsP. The nature of this regulatory gene is unclear at present.