Extensive Diversity of Ionizing-Radiation-Resistant Bacteria Recovered from Sonoran Desert Soil and Description of Nine New Species of the Genus Deinococcus Obtained from a Single Soil Sample

Abstract

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

Response and resilience of soil biocrust bacterial communities to chronic physical disturbance in arid shrublands

“…The majority (74%) of Actinobacteria sequences identified in this study belong to the deepest branch of the phylum, the Rubrobacteridae, which are common in arid soils and on rock surfaces worldwide and are extremely resistant to desiccation and UV stress (Holmes et al, 2000;Rainey et al, 2005). The involvement of Rubrobacteridae in soil aggregate formation and calcite precipitation suggests that they may also be involved in engineering the soil surface structure during biocrust formation (Mummey and Stahl, 2004;Rainey et al, 2005;Mummey et al, 2006;Pellerin et al, 2009).…”

“…The majority (74%) of Actinobacteria sequences identified in this study belong to the deepest branch of the phylum, the Rubrobacteridae, which are common in arid soils and on rock surfaces worldwide and are extremely resistant to desiccation and UV stress (Holmes et al, 2000;Rainey et al, 2005). The involvement of Rubrobacteridae in soil aggregate formation and calcite precipitation suggests that they may also be involved in engineering the soil surface structure during biocrust formation (Mummey and Stahl, 2004;Rainey et al, 2005;Mummey et al, 2006;Pellerin et al, 2009). Filamentous Chloroflexi bacteria have been visualized within sheaths of Microcoleus chthonoplastes in hypersaline microbial mats and co-located with M. vaginatus in biocrusts of a high elevation site in Colorado, but whether the relationship between the two species is symbiotic or antagonistic is not known (Ley et al, 2006;Freeman et al, 2009).…”

Kineococcus xinjiangensis sp. nov., isolated from desert sand

“…Because of our interest in radiation-resistant bacteria and the correlation that has been made between desiccation and radiation resistance (Mattimore & Battista, 1996), we have studied bacteria that survive in the desert. Desiccation-and radiation-resistant bacteria have been observed in several genera, including Deinococcus, Rubrobacter, Hymenobacter, Methylobacterium, Kocuria and Kineococcus (Rainey et al, 2005;Phillips et al, 2002). The genus Kineococcus was first created by Yokota et al (1993) with the species Kineococcus aurantiacus, based on a single strain isolated from soil.…”

“…The pH range (pH 5-10 at intervals of 1 pH unit) for growth was determined in tenfold-diluted marine broth (Difco). In addition, carbohydrate utilization was tested using a defined medium solidified with deionized water-washed agar, as described previously (Rainey et al, 2005). Growth was examined visually on plates incubated at 30 u C for up to 7 days.…”

Endophytic Microbiota Associated with the Root Tips and Leaves of Baccharis dracunculifolia

“…In our study, the order Gaiellales was only found in galled plant roots (0.09%). In contrast to the root samples, the galled leaf samples had a large proportion of Rubrobacterales belonging to the genus Rubrobacter, which are common in arid soils and on rock surfaces worldwide and are extremely resistant to desiccation and UV stress [ 67,68 ]. This finding is notable as B. dracunculifolia is a pioneer species capable of colonizing the extremely harsh habitats of the mountain top rupestrian grasslands.…”