A cell factory of Bacillus subtilis engineered for the simple bioconversion of myo-inositol to scyllo-inositol, a potential therapeutic agent for Alzheimer's disease

Abstract

Background: A stereoisomer of inositol, scyllo-inositol, is known as a promising therapeutic agent for Alzheimer's disease, since it prevents the accumulation of beta-amyloid deposits, a hallmark of the disease. However, this compound is relatively rare in nature, whereas another stereoisomer of inositol, myo-inositol, is abundantly available.

Results: Bacillus subtilis possesses a unique inositol metabolism involving both stereoisomers. We manipulated the inositol metabolism in B. subtilis to permit the possible bioconversion from myo-inositol to scyllo-inositol. Within 48 h of cultivation, the engineered strain was able to convert almost half of 10 g/L myo-inositol to scyllo-inositol that accumulated in the culture medium.

Conclusions: The engineered B. subtilis serves as a prototype of cell factory enabling a novel and inexpensive supply of scyllo-inositol.

Figure 1

Inositol metabolism in B. subtilis. B. subtilis iol genes encoding enzymes for reactions in the inositol catabolic pathway and the respective intermediate compounds are shown. The intermediate compounds are myo-inositol (compound 1), D-chiro-inositol (compound 2), scyllo-inositol I (compound 3), scyllo-inosose (compound 4), 1-keto-D-chiro-inositol (compound 5), 3D-(3,5/4)-trihydroxycyclohexane-1,2-dione (compound 6), 5-deoxy-D-glucuronic acid (compound 7), 2-deoxy-5-keto-D-gluconic acid (compound 8), 2-deoxy-5-keto-D-gluconic acid 6-phosphate (compound 9), dihydroxyacetone phosphate (compound 10), malonic semialdehyde (compound 11), and acetyl-CoA (compound 12).

Figure 2

Inositol stereoisomers present in the medium. Strains of B. subtilis, including YF256 (A), TM038 (B), TM039 (C), TM040 (D), or TM041 (E), were grown in the inositol bioconversion medium containing 2% Bacto soytone. At the indicated time points, aliquots of the culture medium were subjected to GC-TOFMS analysis as described previously [20] in parallel with the initial medium (F) and authentic standards as indicated (G). The experiments were repeated independently at least three times with similar results, and the representative data are shown.

Figure 3

Time course of scyllo-inositol production and myo-inositol consumption during inositol bioconversion along with the cell growth. The bioconversion from myo-inositol to scyllo-inositol was performed in the media containing 2% (A) or 1% (B) Bacto soytone. The data presented are optical density of the cells (black diamonds), and concentration of myo-inositol (black squares) and scyllo-inositol (white triangles). The experiments were repeated independently at least three times with similar results, and the representative data sets are shown.