Advancement of DNA sequencing technology allows the routine use of genome sequences in the various fields of microbiology. The information held in genome sequences proved to provide objective and reliable means in the taxonomy of prokaryotes. Here, we describe the minimal standards for the quality of genome sequences and how they can be applied for taxonomic purposes.

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Strains ofThe genus Deinococcus includes the species Deinococcus radiodurans, Deinococcus proteolyticus, Deinococcus radiophilus, and Deinococcus radiopugnans. The species Deinococcus erythromyxa was also included in this genus as a species incertae sedis by Brooks and Murray (3). The rod-shaped organisms of the species Deinococcus grandis are very closely related to the species of the genus Deinococcus, but were classified in the genus Deinococcus primarily on the basis of morphology (36). Recently, the type strains of these species were subjected to a complete 16s ribosomal DNA (rDNA) sequence analysis, which resulted in the reclassification of Deinococcus grandis and Deinococcus erythromyxa (41). The species Deinococcus grandis, despite its rod-shaped morphology, falls within the radiation of the genus Deinococcus and for this reason was classified as Deinococcus grandis. The species Deinococcus erythromyxa was known by Brooks and Murray (3) to have characteristics that were different from those of the other species of Deinococcus, and subsequent studies confirmed its chemotaxonomic distinctiveness, which reinforced the need for reclassification of this species (12). The species Deinococcus erythromyxa has been found to be phylogenetically very closely related to the gram-positive species Kocuria rosea, but due to the low DNA-DNA hybridization values between the two species, Kocuria erythromyxa was maintained as a separate speciesThe species of the genus Deinococcus are strictly aerobic, have optimum growth temperatures in the range from 25 to 35"C, produce reddish colonies, generally stain gram positive, have ornithine in the peptidoglycan, lack teichoic acids, possess menaquinone 8 as the major respiratory quinone, and are (41).

The ionizing-radiation-resistant fractions of two soil bacterial communities were investigated by exposing an arid soil from the Sonoran Desert and a nonarid soil from a Louisiana forest to various doses of ionizing radiation using a 60 Co source. The numbers of surviving bacteria decreased as the dose of gamma radiation to which the soils were exposed increased. Bacterial isolates surviving doses of 30 kGy were recovered from the Sonoran Desert soil, while no isolates were recovered from the nonarid forest soil after exposure to doses greater than 13 kGy. The phylogenetic diversities of the surviving culturable bacteria were compared for the two soils using 16S rRNA gene sequence analysis. In addition to a bacterial population that was more resistant to higher doses of ionizing radiation, the diversity of the isolates was greater in the arid soil. The taxonomic diversity of the isolates recovered was found to decrease as the level of ionizing-radiation exposure increased. Bacterial isolates of the genera Deinococcus, Geodermatophilus, and Hymenobacter were still recovered from the arid soil after exposure to doses of 17 to 30 kGy. The recovery of large numbers of extremely ionizing-radiationresistant bacteria from an arid soil and not from a nonarid soil provides further ecological support for the hypothesis that the ionizing-radiation resistance phenotype is a consequence of the evolution of other DNA repair systems that protect cells against commonly encountered environmental stressors, such as desiccation. The diverse group of bacterial strains isolated from the arid soil sample included 60 Deinococcus strains, the characterization of which revealed nine novel species of this genus.Extreme ionizing-radiation resistance has been observed in several members of the domains Bacteria and Archaea. Of the genera containing ionizing-radiation-resistant organisms, Deinococcus and Rubrobacter show the highest levels of resistance, and all species of these genera have been shown to be

SummaryThe accumulation of organic solutes is a prerequisite for osmotic adjustment of all microorganisms. Thermophilic and hyperthermophilic organisms generally accumulate very unusual compatible solutes namely, di-myo -inositol-phosphate, di-mannosyl-di-myoinositol-phosphate, di-glycerol-phosphate, mannosylglycerate and mannosylglyceramide, which have not been identified in bacteria or archaea that grow at low and moderate temperatures. There is also a growing awareness that some of these compatible solutes may have a role in the protection of cell components against thermal denaturation. Mannosylglycerate and di-glycerol-phosphate have been shown to protect enzymes and proteins from thermal denaturation in vitro as well, or better, than compatible solutes from mesophiles. The pathways leading to the synthesis of some of these compatible solutes from thermophiles and hyperthermophiles have been elucidated. However, large numbers of questions remain unanswered. Fundamental and applied interest in compatible solutes and osmotic adjustment in these organisms, drives research that, will, in the near future, allow us to understand the role of compatible solutes in osmotic protection and thermoprotection of some of the most fascinating organisms known on Earth.