The vitamin B6 biosynthesis pathway in Streptococcus pneumoniae is controlled by pyridoxal 5=-phosphate and the transcription factor PdxR and has an impact on ear infection

Vitamin B6 is an essential cofactor for a large number of enzymes in both prokaryotes and eukaryotes. In this study, we charac-terized the pyridoxal 5=-phosphate (PLP) biosynthesis pathway in Streptococcus pneumoniae. Our results revealed that S. pneu-moniae possesses a de novo vitamin B6 biosynthesis pathway encoded by the pdxST genes. Purified PdxS functionally displayed as PLP synthase, whereas PdxT exhibited glutaminase activity in vitro. Deletion of pdxS, but not pdxT, resulted in a vitamin B6 auxotrophic mutant. The defective growth of thepdxSmutant in a vitamin B6-depleted medium could be chemically restored in the presence of the B6 vitamers at optimal concentrations. By analyzing PdxS expression levels, we demonstrated that the ex-pression of pdxSwas repressed by PLP and activated by a transcription factor, PdxR. A pneumococcalpdxRmutant also exhib-ited as a vitamin B6 auxotroph. In addition, we found that disruption of the vitamin B6 biosynthesis pathway in S. pneumoniae caused a significant attenuation in a chinchilla middle ear infectionmodel and a minor attenuation in a mouse pneumonia model, indicating that the impact of vitamin B6 synthesis on virulence depends upon the bacterial infection niche. Vitamin B6 represents the most versatile organic cofactor ofenzymes in all organisms. It refers to six biologically intercon-vertible compounds or vitamers: pyridoxine (PN), pyridoxamine (PM), pyridoxal (PL), and their respective phosphorylated forms, including pyridoxine 5=-phosphate (PNP), pyridoxamine 5=-phosphate (PMP), and pyridoxal 5=-phosphate (PLP) (1). PLP i