Vitamin B6 metabolism in the Gram-positive model bacterium Bacillus subtilis

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The term "vitamin B6" collectively designates the vitamers pyridoxal (PL), pyridoxine (PN), and pyridoxamine (PM), and the respective phosphate esters pyridoxal 5’-phosphate (PLP), pyridoxine 5’-phosphate (PNP), and pyridoxamine 5’-phosphate (PMP). PLP is the most important B6 vitamer because it serves as a cofactor for many proteins and enzymes. In the Gram-positive model bacterium Bacillus subtilis at least 65 proteins require PLP for function. B. subtilis relies on the deoxyxylulose-phosphate (DXP)-independent PdxST enzyme complex for PLP synthesis. Other organisms synthesize PLP via the DXP-dependent pathway, which involves seven enzymatic reactions. It has also been observed that B. subtilis can take up the B6 vitamers PL and PN from the environment to produce PLP. However, the transport systems for the B6 vitamers are unknown. In the proposed project, we want to identify the first bacterial vitamin B6 transporter. Moreover, we aim to elucidate the role of the glutaminase PdxT in PLP synthesis and how the reactive B6 vitamer is transferred to the target proteins. Recently, we have found that two genomic alterations are sufficient to allow a B. subtilis strain to produce PLP via a truncated DXP-dependent pathway consisting of only two non-native enzymes. Genetic analyses revealed that the YtoQ protein of unknown function is involved in vitamin B6 biosynthesis. By applying genetic as well as biochemical approaches we aim to elucidate the physiological role of the YtoQ protein. Furthermore, to unravel how the novel vitamin B6 biosynthetic route operates, we will perform metabolome analyses.