The fine structure of Micrococcus radiophilus and Micrococcus radioproteolyticus

The radiation resistant bacteria Micrococcus radiophilus and M. radioproteolyticus were studied by thin sectioning and freeze-etching techniques and the two species were found to be similar in the fine structure. The only significant difference was in the appearance of the surfaces of the cell walls in freeze-etched preparations.Since the two species, together with M. radiodurans, possess a unique cell wall structure and a cell wall peptidoglycan, which is different from that of other micrococci and Gram-positive cocci, it is recommended that they be reclassified into a new genus.     

Lysis of Micrococcus radiodurans

Two sulfur containing peptides have been isolated from a cationic peptide-rich fraction of dried Lentinus edodes by Chromatographic technic. They have been identified as γ-glutamylcystine and N,N-bis-³-glutamylcystinylglycine based on chemical, Chromatographic and spectroscopic properties.     

Ecology of Micrococcus radiodurans

An ecological study of Micrococcus radiodurans indicated that microorganisms possessing the same morphological and radiation-resistance characteristics as that organism could be isolated from ground beef and from pork sausage. Further studies showed that such organisms also could be isolated from beef hides and from water from a creek adjacent to the packing plant from which the meat samples were obtained. Similar microorganisms were not isolated, however, from a limited number of samples of soil, hay, and fecal material. The use of high levels of gamma-radiation in the initial isolation procedures proved to be advantageous in inactivating most of the other microflora and facilitating the isolation of M. radiodurans. Control experiments indicated that M. radiodurans did not compete well with the microflora present in ground meat, soil, and beef hides. Preincubation before irradiation of meat and soil samples or enrichment culture techniques did not enhance the isolation of M. radiodurans. The presence of M. radiodurans in creek water suggested one possible source of this organism.     

Antibiotic Sensitivity of Micrococcus radiodurans

A wild-type strain of Micrococcus radiodurans and its nonpigmented mutant W(1) were tested for sensitivity to 10 antibiotics selected from the standpoint of their mechanism of action. Representatives of groups of antibiotics inhibiting deoxyribonucleic acid (DNA) synthesis, DNA-dependent ribonucleic acid synthesis, protein synthesis, and cell wall synthesis were selected. M. radiodurans and its mutant exhibited full susceptibility to all antibiotics tested (mitomycin C, actinomycin D, chloramphenicol, dihydrostreptomycin, erythromycin, neomycin, kanamycin, benzylpenicillin, bacitracin, and vancomycin), the degree of susceptibility being of the same order as that of a standard strain of Staphylococcus aureus 209 P, with the exception of dihydrostreptomycin.     

Glucose Catabolism in Micrococcus sodonensis

The inability of Micrococcus sodonensis to grow on glucose as the sole source of carbon and energy was investigated. Estimation of pathways of glucose catabolism indicated that both the glycolytic and hexose monophosphate pathways are present in this organism. Comparative studies with Escherichia coli demonstrated that key enzymes for glucose catabolism were present in M. sodonensis in quantities equivalent to those of E. coli. The glucose-6-phosphate and 6-phosphogluconate dehydrogenases of M. sodonensis were nicotinamide adenine dinucleotide phosphate (NADP) specific, and glyceraldehyde-3-phosphate dehydrogenase was nicotinamide adenine dinucleotide specific. Transhydrogenase and reduced NADP oxidase were absent. Growth of the organism in the presence of glucose did not result in a repressed ability to oxidize tricarboxylic acid cycle intermediates, but these cells did have a decreased capacity for glucose degradation. The addition of substrates rich in growth-promoting substances, e.g., yeast extract, did not provide requisite nutrients for growth on glucose. Studies with (32)P suggest that M. sodonensis is incapable of synthesizing energy-rich phosphate compounds during the catabolism of glucose.     

Radioresistance mechanisms of Micrococcus radiodurans

The modern conceptions on the molecular mechanisms of Micrococcus radiodurans viability under the action of ionized radiation have been considered. Factors providing a high level of the bacterium radioresistance-the peculiarities of the cell wall structure, membranes, DNA, the redundancy of genetic information, the multiplicity of sites of DNA attachment to the membrane, a high level of antioxidant and antiradical systems-have been analysed. It has been shown that the efficiency of accurate, error-free, well balanced DNA repair system in connection with M. radiodurans properties mentioned provides a high radiation resistance of this microorganism.