The most resistant of all known non–sporeforming bacteria consist of four species of the genus Deinococcus and one each of Deinobacter, Rubrobacter, and Acinetobacter. Some characteristics of these species are presented in Table 15–8.
The deinococci were originally assigned to the genus Micrococcus, but they, along with Deinobacter and the archaebacterial genus, Thermus, constitute one of the ten major phyla based on 16S ribosomal RNA (rRNA).90,93,96 The deinococci occur in pairs or tetrads, contain red water-insoluble pigments, have optimum growth at 30◦C, contain l-ornithine as the basic amino acid in their murein (unlike the micrococci, which contain lysine), and are characterized by mol% G + C content between 62 and 70. They do not contain teichoic acids.
They have been characterized as being Gram-negative clones of ancient lineage.11 Among other unusual features of deinococci is their possession of palmitoleate (16:1), which makes up about 60% of the fatty acids in their envelope and about 25% of the total cellular fatty acid. The high content of fatty acids is another feature characteristic of Gram-negative bacteria. The predominant isoprenoid quinone in their plasma membrane is a menaquinone.
The menaquinones represent one of the two groups of naphthoquinones that are involved in electron transport, oxidative phosphorylation, and perhaps active transport.9 The length of the C-3 isoprenyl side chains ranges from 1 to 14 isoprene units (MK), and the deinococci are characterized by the possession of MK-8, as are some micrococci, planococci, staphylococci, and enterococci.9