Summary auto-generated
Researchers isolated a novel Gram-positive bacterium, designated Kineococcus radiotolerans sp. nov., from a radioactive work area at the Savannah River Site in South Carolina. The orange-pigmented, coccus-shaped organism exhibits remarkable resistance to gamma radiation and desiccation. Analysis shows 93% 16S rRNA gene sequence similarity to Kineococcus aurantiacus but only 31% DNA-DNA hybridization similarity, confirming it as a distinct species. The bacterium grows at temperatures between 11-41°C and pH 5-9, with a doubling time of 2.5 hours at 32°C. Its lipid composition is dominated by anteiso 15:0 fatty acids (≥90%), with unusual long-chain alkenes of 19-24 carbons. K. radiotolerans demonstrates exceptional gamma radiation tolerance comparable to the highly resistant Deinococcus radiodurans, with no logarithmic killing observed at doses up to 3.5 kGy. The strain is motile via polar flagella and produces an orange carotenoid pigment with characteristic absorption peaks. Phylogenetic analysis places it within the Actinobacteria, likely in the family Pseudonocardiaceae.
Key findings
- K. radiotolerans is a novel species with exceptional gamma radiation resistance comparable to Deinococcus radiodurans, showing survival at doses up to 3.5 kGy
- The organism exhibits 93% 16S rRNA similarity to K. aurantiacus but only 31% DNA-DNA hybridization, establishing it as a genetically distinct species
- K. radiotolerans produces unusual long-chain alkenes (19-24 carbons) as neutral lipids, a rare characteristic in terrestrial bacteria
- The strain shows high desiccation resistance similar to D. radiodurans, suggesting a physiological link between radiation and desiccation tolerance
- K. radiotolerans grows optimally at 32°C with doubling time of 2.5 hours and utilizes diverse carbon sources including glucose, arabinose, and mannitol
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Abstract
A Gram-type positive, motile, coccus-shaped organism was isolated from a radioactive work area. Strain SRS30216(T) is an orange-pigmented bacterium that is catalase-positive, oxidase-negative and urease-negative. The orange pigment is most likely a carotenoid with absorption peaks at approximately 444, 471 and 501 nm. Cells normally grew in clusters, but individual, motile, flagellated cells were also observed. Growth of strain SRS30216(T) occurred at temperatures between 11 and 41 degrees C, between pH 5 and 9 and at NaCl concentrations up to and including 5%. Fatty acid composition was limited, with > 90% of the fatty acids being anteiso 15:0. Alkenes of 19--24 carbons in length were detected during examination of the neutral lipids. Strain SRS30216(T) demonstrated high levels of resistance to gamma-radiation and desiccation. The most closely related recognized species is Kineococcus aurantiacus RA 333(T), which is 93% similar in 16S rDNA sequence. DNA--DNA hybridization revealed only 31% similarity between these two organisms. It is proposed that SRS30216(T) (=ATCC BAA-149(T)=DSM 14245(T)) represents the type strain of a novel species in the genus Kineococcus, Kineococcus radiotolerans sp. nov.