Various subspecies of Bacteroides melaninogenicus differ in their pigmentation. Subsp. asaccharolyticus produces protohaem almost exclusively, subsp. intermedicus both protohaem and a smaller proportion of protoporphyrin, and subsp. melaninogenicus mainly protoporphyrin with a trace of protohaem. As a consequence young colonies can be differentiated by their red fluorescence in u.v. light (365nm): subsp. asaccharolyticus does not fluoresce, subsp. intermedicus shows a limited fluorescence, and subsp. melaninogenicus shows a bright fluorescence. The pigments were isolated as the dimethyl esters of protohaemin and of protoporphyrin and identified by electronic spectroscopy, mass spectrometry and comparisons by t.l.c. Incorporation of delta-aminolaevulinate into these pigments was not detected, nor was porphobilinogen formation observed. Subsp. melaninogenicus grown in the presence of [14C]protohaemin formed [14C]protoporphyrin. This appears to represent a novel biological demetallation.

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