The Vitamin B 6 Biosynthesis Pathway in Streptococcus pneumoniae Is Controlled by Pyridoxal 5′-Phosphate and the Transcription Factor PdxR and Has an Impact on Ear Infection

Abstract

ABSTRACT Vitamin B 6 is an essential cofactor for a large number of enzymes in both prokaryotes and eukaryotes. In this study, we characterized the pyridoxal 5′-phosphate (PLP) biosynthesis pathway in Streptococcus pneumoniae . Our results revealed that S. pneumoniae possesses a de novo vitamin B 6 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 B 6 auxotrophic mutant. The defective growth of the Δ pdxS mutant in a vitamin B 6 -depleted medium could be chemically restored in the presence of the B 6 vitamers at optimal concentrations. By analyzing PdxS expression levels, we demonstrated that the expression of pdxS was repressed by PLP and activated by a transcription factor, PdxR. A pneumococcal Δ pdxR mutant also exhibited as a vitamin B 6 auxotroph. In addition, we found that disruption of the vitamin B 6 biosynthesis pathway in S. pneumoniae caused a significant attenuation in a chinchilla middle ear infection model and a minor attenuation in a mouse pneumonia model, indicating that the impact of vitamin B 6 synthesis on virulence depends upon the bacterial infection niche.