Porphyromonas endodontalis binds, reduces and grows on human hemoglobin

Porphyromonas endodontalis is a black-pigmented, obligate anaerobic rod-sha ped bacterium implicated as playing a major role in endodontic infections. We have previously shown that P. endondontalis requires the porphyrin nucle us, preferably supplied as hemoglobin, as a growth supplement. The bacteria also actively transport free iron, although this activity does not support growth in the absence of a porphyrin source. The purpose of this study was to further investigate the binding and subsequent utilization of human hem oglobin by P. endodontalis. P. endodontalis binds hemoglobin and reduces th e Fe(III) porphyrin, resulting in a steady accumulation of ferrous hemoglob in. Reduction of methemoglobin was similar to the extracellular reduction o f nitrobluetetrazolium in the presence of oxidizable substrate. Turbidimetr ic and viable cell determinations showed that P. endodontalis grew when sup plied only hemoglobin. Therefore, we conclude that hemoglobin appears to se rve as a sole carbon and nitrogen source, and that these bacteria reduce ex tracellular compounds at the expense of oxidized substrates.