Link to bioRxiv paper: http://biorxiv.org/cgi/content/short/2020.07.23.218966v1?rss=1 Authors: McDevitt, E., Khan, F., Scasny, A., Eichembaun, Z., McDaniel, L. S., Vidal, J. E. Abstract: Streptococcus pneumoniae (Spn) and other streptococci produce a greenish halo on blood agar plates referred to as -hemolysis. This phenotype is utilized by clinical microbiology laboratories to report culture findings of -hemolytic streptococci, including Spn, and other bacteria. The -hemolysis halo on blood agar plates has been related to the hemolytic activity of pneumococcal pneumolysin (Ply), or to a lesser extent, to lysis of erythrocytes by Spn-produced hydrogen peroxide. We investigated the molecular basis of the -hemolysis halo produced by Spn. Wild-type strains TIGR4, D39, R6, and EF3030, and isogenic derivative {Delta}ply mutants, produced a similar -hemolytic halo on blood agar plates while cultures of hydrogen peroxide knockout {Delta}spxB/{Delta}lctO mutants lacked this characteristic halo. Spectroscopic studies demonstrated that culture supernatants of TIGR4 released hemoglobin-bound heme (heme-hemoglobin) from erythrocytes and oxidized oxy-hemoglobin to met-hemoglobin within 30 min of incubation. As expected, given Ply hemolytic activity, and that hydrogen peroxide contributes to the release of Ply, TIGR4 isogenic mutants {Delta}ply and {Delta}spxB/{Delta}lctO had a significantly decreased release of heme-hemoglobin from erythrocytes. However, TIGR4Dply that produces hydrogen peroxide oxidized oxy-hemoglobin to met-hemoglobin, whereas TIGR4{Delta}spxB/{Delta}lctO failed to produce oxidation of oxy-hemoglobin. We demonstrated that the so-called -hemolysis halo is caused by the oxidation oxy-hemoglobin (Fe+2) to a non-oxygen binding met-hemoglobin (Fe+3) by Spn-produced hydrogen peroxide. Since Spn colonizes the human lung, oxidation of oxy-hemoglobin might have important implications for pathogenesis. Copy rights belong to original authors. Visit the link for more info