Fifty strains of red-pigmented, gram-positive, nonfermentative micrococci were studied, including organisms from diverse collections identified as and “” and miscellaneous unidentified strains usually labelled (names in quotation marks are not on the Approved Lists of Bacterial Names, Int. J. Syst. Bacteriol. :225–420, 1980). Although similar in physiological attributes (negative characters predominated), the cell wall structural profiles separated and (simple homogeneous profile) from “” and the radiation-resistant group (complex, multilayered profile). Simple reactions (growth in 5% NaCl broth, growth at 37°C, and nitrate reduction) distinguished from , and acid production from glucose and other sugars distinguished “” from the rest. The members of the “” group could be typified by physiological reactions but not with great reliability. Gas-liquid chromatography of extracted lipids showed that veritable and strains had at least 50% of fatty acids in the form of 15:0 branched chains. “” and the rest had straight chains with a 16:1 component which formed at least 25% of total fatty acids and which was not possessed by or . Further studies were based on representative strains of clusters derived from the above-mentioned tests. Zymograms for nonspecific esterases and chromatograms of extracted pigments showed no identical patterns for any 2 of 10 strains. Absorption spectra for pigments had maxima at 450 to 510 nm. The guanine plus cytosine contents of the deoxyribonucleic acids ranged from 62 to 74 mol%: The cluster was >69 mol%, and the radiation-resistant cluster was < 71 mol%. There was little deoxyribonucleic acid homology between and (8%) or among any of the rest (< 21%). The named radiation-resistant species showed <18% homology to each other, but alignments were detected in the miscellaneous group. Ribosomal ribonucleic acid (16S) cataloguing showed that “,” “,” and one of the miscellaneous radiation-resistant strains were related ( = 0.51 to 0.63) but that they had as little oligonucleotide similarity to and ( = 0.23) as they all did to . It is concluded that “” and its relatives are not species of and that they represent clones that separated from the main stem early in procaryotic evolution. There are at least five such species: , and one other unnamed.


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