Genetics of the Resistance to and Production of H2O2 in Streptococcus pneumoniae

Abstract

Streptococcus pneumoniae (Pneumococcus) is a causative agent of severe diseases affecting young as well as older people. Pneumococcus produces very high levels of hydrogen peroxide (H<sub>2</sub>O<sub>2</sub>) (>1 mM). In the presence of pneumolysin, H<sub>2</sub>O<sub>2</sub> has been shown to cause pneumococcal meningitis in humans. H<sub>2</sub>O<sub>2</sub> is a by-product of oxidation of pyruvate by the pyruvate oxidase, SpxB, during the generation of acetyl PO<sub>4</sub> in pneumococcus. Acetyl PO<sub>4</sub> then is utilized to make ATP. Current work focuses on manipulating the genome to study the role of H<sub>2</sub>O<sub>2</sub> in pneumococcal pathogenesis. Previously, pneumococcal cells pregrown in the presence of lactose were shown to have an increased resistance (10−fold) to H<sub>2</sub>O<sub>2</sub> challenge. Random mutagenesis showed that the genes pyrB, truB, spr1639, and spr1813 are responsible for the resistance. Based on the DNA sequence data, it has been speculated that the spxB operon is mono-cistronic and expressed constitutively. Our experimental evidence, however, showed that maximal production of H<sub>2</sub>O<sub>2</sub> is linked to the onset of stationary phase under static growth conditions or exposure to molecular oxygen while the transcriptional activity of spxB was constitutive even during the exponential phase of growth. Also, insertion of a reporter gene immediately down stream of the spxB gene resulted in normal H<sub>2</sub>O<sub>2</sub> production implying that glyoxalase, a co-transcript of spxB, is not required for H<sub>2</sub>O<sub>2</sub> production and other factors besides SpxB are needed for H<sub>2</sub>O<sub>2</sub> production in this pathogen. We speculate that the generation of this toxin is linked to either quorum-sensing and/or availability of nutrient resources. Together, the findings helped to expand the pathogenesis pathway of H<sub>2</sub>O<sub>2</sub> in S. pneumoniae.