Five bacterial strains have been isolated from dust samples collected from the upper troposphere and lower stratosphere during several aircraft flights. Most of them displayed much higher resistance to ultraviolet radiation (254 nm) than surface airborne isolates. The role of UV radiation combined with other conditions to determine survivability of bacterial species in the upper atmosphere is discussed. Two strains from the upper atmosphere (ST0316 and TR0125) exhibited extreme UV resistance and tend to form cell clumps or aggregates. Forming cell aggregation might be a strategy to enhance their survivability in the harsh conditions such as high dosage of UV at high altitude.
An orange-pigmented, non-motile, coccoid bacterial strain, designated TR0125T , was isolated from dust samples collected in the high atmosphere above Japan. Phylogenetic analysis based on 16S rRNA gene sequences showed that the strain was within the radiation of Deinococcus species. The major peptidoglycan amino acids were D-glutamic acid, glycine, D-alanine, L-alanine and ornithine. The predominant fatty acids were iso-C 17 : 0 , iso-C 17 : 1 v9c and iso-C 15 : 0 . Strong resistance to desiccation, UV-C and gamma radiation and high DNA G+C content also supported the affiliation of strain TR0125 T to the genus Deinococcus. Strain TR0125 T showed the highest 16S rRNA gene sequence similarity value (95.7 %) to the type strain of Deinococcus apachensis, and phylogenetic analysis showed that it was further separated from D. apachensis than from Deinococcus geothermalis, indicating that strain TR0125 T was not a member of these two Deinococcus species. In addition, phenotypic differences were found between strain TR0125 T and the type strains of these two Deinococcus species. Therefore, a novel species of the genus Deinococcus, Deinococcus aerius sp. nov. (type strain, TR0125 T 5JCM 11750T 5DSM 21212 T ), is proposed to accommodate this isolate.
A pink-red pigmented, non-motile, coccoid bacterial strain, ST0316 T , was isolated from dust samples collected from the stratosphere in Japan. Phylogenetic analysis based on 16S rRNA gene sequences showed that it belonged to the genus Deinococcus. DNA G+C content (69.8 mol%), desiccation tolerance, and resistance to gamma-rays [D 10 (dose required to reduce the bacterial population by 10-fold Members of the genus Deinococcus, which houses 34 species at the time of writing, are known to be desiccation-and radiation-resistant, and have been isolated from various natural environments. It has been suggested that deinococci may become airborne and be distributed throughout the environment (Battista & Rainey, 2001). Actually, some strains belonging to the genus Deinococcus have been isolated from air dust sources (Murray & Robinow, 1958;Christensen & Kristensen, 1981; Weon et al., 2007;Yang et al., 2009). In a previous study, we obtained a novel UVresistant strain from an air dust sample collected in the stratosphere (Yang et al., 2008). Here we report the detailed characterization of this isolate, ST0316 T .We tested the growth of strain ST0316 T on nutrient agar no. 2 (10.0 g peptone, 10.0 g meat extract and 5.0 g NaCl per litre, pH 7.0±0.2), Difco nutrient (3.0 g beef extract, 5.0 g peptone per litre, pH 6.8±0.2), ATCC medium 86 (Difco nutrient with 1 % glucose), Degryse medium 162 (Degryse et al., 1978), TGY (1 % tryptone, 0.1 % glucose, 0.5 % yeast extract, pH 7.0±0.2) and mTGE (6.0 g beef extract, 10.0 g tryptone, 2.0 g glucose per litre, pH 7.0±0.2). Like some deinococcal isolates from the Sonoran Desert (Rainey et al., 2005), ST0316 T grew extremely slowly or not at all in liquid media. Its growth on solid agar containing the above nutrients was also slow, although faster than in the respective liquid medium. Addition of glycerol (0.5 %) and KH 2 PO 4 (0.1 mM) to mTGE agar (namely mTGE-GP) slightly accelerated its growth. Unless stated otherwise, ST0316T cells used in this study were obtained from cultures grown for 3 weeks on mTGE-GP, incubated in the dark at 30 u C. Growth temperatures were measured by spreading cells on mTGE-GP, incubating at 4, 10, 15, 20, 23, 25, 28, 30, 32, 35, 40, 42 or 45 u C for 4 weeks, and checking the development of colonies on the agar plates. The pH range for growth was determined on mTGE-GP plates with the medium buffered between pH 5.8 and pH 8.0 (0.2 pH unit intervals) with 10 mM potassium phosphate buffer.The GenBank/EMBL/DDBJ accession number for the 16S rRNA gene sequence of strain ST0316T is AB087287.A graph showing gamma-ray resistance of strain ST0316 T , polar lipid profiles, and phenotypic characteristics and fatty acid compositions of strain ST0316T and the type strains of the closest related species of the genus Deinococcus are available with the online version of this paper.
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