Luteolin Phosphate Derivatives Generated by Cultivating Bacillus subtilisvar. Natto BCRC 80517 with Luteolin

Luteolin (LUT), a plant-derived flavone, exhibits various bioactivities; however, the poor aqueous solubility hampers its applications. Here, we revealed bioconversion of LUT by Bacillus subtilisBCRC 80517, yielding three water-soluble phosphate conjugates. These derivatives were identified as luteolin 4′-O-phosphate (L4′P), luteolin 3′-O-phosphate (L3′P), and luteolin 7-O-phosphate (L7P) by LC-ESI-MS/MS and NMR. Besides, we found that Bacillus subtilisBCRC 80517 was able to convert different levels of LUT but showed a limited conversion rate. By observing bacterial morphology with transmission electron microscopy and confocal fluorescence microscopy, we found that LUT disrupted the bacterial membrane integrity, which explained the incomplete conversion. Additionally, we revealed a spontaneous intramolecular transesterification of L4′Pto L3′P, the thermodynamically more stable form, under acidic conditions and proposed the possible mechanism involving a cyclic phosphate as the intermediate. This study provides insight into development of a potent structural modification strategy to enhance the solubility of LUT through biophosphorylation.