Tetrapyrrole utilization by Bacteroides fragilis

Abstract

During growth in a defined medium containing protoheme, Bacteroides fragilis strain 2044 and Bacteroides "ℓ" 7CM formed protoheme-containing b-type cytochromes. The major reduced versus oxidized spectral peaks found for strain 2044 were at 562 and 428 nm whereas the peaks observed for strain 7CM were at 559 and 427 nm. When protoheme was replaced by deuteroporphyrin, mesoporphyrin, or their manganese or magnesium chelates, both organisms formed deuteroheme- or mesoheme-containing cytochromes with difference spectral peaks at 546 to 547 nm and 411 to 413 nm. Pyridine hemochromogen spectra of cells grown in the presence of tetrapyrroles containing the deuteroporphyrin or mesoporphyrin moiety confirmed the presence of deuteroheme or mesoheme in the cells. Although capable of delayed and relatively scant growth in media devoid of added tetrapyrroles or in media containing the vanadium chelates of mesoporphyrin or deuteroporphrin, neither organism formed cytochromes under these growth conditions. The functional nature of the cytochromes containing deuteroheme or mesoheme was confirmed by their reduction by cells in the presence of 56 mM glucose and carbon dioxide compared with cells exposed to air. The use of tetrapyrroles by strains 2044 and 7CM is similar to that previously found for Bacteroides ruminicola ssp. ruminicola. Versatility in tetrapyrrole utilization for cytochrome synthesis appears to be a common characteristic of heme-requiring gastrointestinal Bacteroides species.