Cytochromes and other pigments of dissimilatory sulphate-reducing bacteria

Summary A survey was made of various visible light absorption spectra of whole cells, particulate and soluble fractions and haem extracts of representative strains of all known species of sulphate-reducing bacteria. The previously accepted distinction that Desulfovibrio species contain only a c-type cytochrome whereas Desulfotomaculum species contain only a b-type cytochrome was not confirmed. The pigment contents of the genera Desulfovibrio and Desulfotomaculum were not completely distinct from each other, but both genera had characteristic spectral patterns. Reduced minus oxidized spectra of whole cells and particulate fractions showed the presence of b-type cytochromes in all Desulfotomaculum species and in Desulfovibrio africanus. However, protohaem, the prosthetic group of b-type cytochromes, occurred in haem extracts from all species, although only just detectable in the extract from Desulfovibrio vulgaris NCIB 8303. Particulate c-type cytochromes were found in Desulfotomaculum orientis, Desulfotomaculum nigrificans and all the Desulfovibrio species, but the amount in Desulfotomaculum nigrificans was very small. Only the Desulfovibrio species contained soluble c-type cytochromes. Spectral properties indicated that a d-type cytochrome might exist in species in addition to Desulfovibrio africanus, but no supporting evidence was obtained from results of haem extractions. Some spectra contained peaks which could not be identified.