Summary auto-generated
Researchers isolated six aromatic-degrading bacterial strains from deep Atlantic coastal plain sediments and performed comprehensive taxonomic analysis. Phylogenetic analysis of 16S rRNA gene sequences, combined with morphological, biochemical, and molecular characterization, demonstrated that five of the six strains belong to the genus Sphingomonas and represent three previously undescribed species. These five strains were gram-negative, nonmotile, rod-shaped bacteria producing yellow colonies, with GC contents ranging from 60.0-65.4 mol% and ubiquinone Q-10 as the predominant quinone. All five strains could degrade aromatic compounds including xylene, toluene, and naphthalene, with degradative genes located on plasmids rather than chromosomes. The three new species are formally proposed: Sphingomonas aromaticivorans, Sphingomonas subterranea, and Sphingomonas stygia. The sixth strain clustered separately and appeared most closely related to Blastobacter natatorius. These subsurface Sphingomonas isolates demonstrate significant biotechnological potential for bioremediation applications in contaminated groundwater.
Key findings
- Five aromatic-degrading strains from deep subsurface sediments represent three new Sphingomonas species: S. aromaticivorans, S. subterranea, and S. stygia, distinguished by 16S rRNA sequences, DNA-DNA reassociation values, and physiological traits
- The five new Sphingomonas species degrade multiple aromatic compounds (xylene, toluene, naphthalene) via plasmid-encoded genes, distinguishing them from surface strains with chromosomal degradative genes
- Subsurface strains showed characteristic Sphingomonas properties: gram-negative, nonmotile rods, yellow pigmentation, ubiquinone Q-10, GC content 60.0-65.4 mol%, and oxidative acid production from carbohydrates
- The sixth subsurface strain (B0477) clustered distinctly with Blastobacter natatorius rather than Sphingomonas species, indicating separate taxonomic status
- Sphingomonas species isolated from deep subsurface environments have significant bioremediation potential due to their ability to degrade diverse petroleum hydrocarbons and related contaminants
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Abstract
Phylogenetic analyses of 16S rRNA gene sequences by distance matrix and parsimony methods indicated that six strains of bacteria isolated from deep saturated Atlantic coastal plain sediments were closely related to the genus Sphingomonas. Five of the strains clustered with, but were distinct from, Sphingomonas capsulata, whereas the sixth strain was most closely related to Blastobacter natatorius. The five strains that clustered with S. capsulata, all of which could degrade aromatic compounds, were gram-negative, non-spore-forming, non-motile, rod- shaped organisms that produced small, yellow colonies on complex media. Their G + C contents ranged from 60.0 to 65.4 mol%, and the predominant isoprenoid quinone was ubiquinone Q-10. All of the strains were aerobic and catalase positive. Indole, urease, and arginine dihydrolase were not produced. Gelatin was not liquified, and glucose was not fermented. Sphingolipids were present in all strains; 2OH14:0 was the major hydroxy fatty acid, and 18:1 was a major constituent of cellular lipids. Acid was produced oxidatively from pentoses, hexoses, and disaccharides, but not from polyalcohols and indole. All of these characteristics indicate that the five aromatic-degrading strains should be placed in the genus Sphingomonas as currently defined. Phylogenetic analysis of 16S rRNA gene sequences, DNA-DNA reassociation values, BOX-PCR genomic fingerprinting, differences in cellular lipid composition, and differences in physiological traits all indicated that the five strains represent three previously undescribed Sphingomonas species. Therefore, we propose the following new species: Sphingomonas aromaticivorans (type strain, SMCC F199), Sphingomonas subterranea (type strain, SMCC B0478), and Sphingomonas stygia (type strain, SMCC B0712).