Morphological, Physiological, and Molecular Characterization of a Newly Isolated Steroid-Degrading Actinomycete, Identified as Rhodococcus ruber Strain Chol-4
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The aerobic degradation of cholesterol, testosterone, androsterone, progesterone, and further steroid compounds as sole carbon source has been observed in the newly isolated bacterial Gram-positive strain Chol-4. The 16S rRNA gene sequence shares the greatest similarity with members of the genus Rhodococcus, with the closest shared nucleotide identities of 98–99% with Rhodococcus ruber (DSM 43338T) and Rhodococcus aetherivorans (DSM 44752T). Phylogenetic analysis of Rhodococcus 16S rRNA gene sequences consistently places strain Chol-4 in a clade shared with those both type strains within the Rhodococcus rhodochrous subclade. The results of DNA–DNA hybridization against its two phylogenetically closest neighbors as well as the results of morphological, physiological, and biochemical tests allowed genotypic and phenotypic differentiation of strain Chol-4 from Rhodococcus ruber (DSM 43338T) on the species level and from the other validly described Rhodococcus species on the genus level. Strain Chol-4 therefore merits recognition as a novel strain of the species Rhodococcus ruber and demonstrates for the first time the capability of this species to utilize a great variety of steroid compounds as growth substrates never shown for other species of this genus so far. The genome of strain Chol-4 harbors at least one gene cluster that may be responsible for the degradation of steroid compounds. This gene cluster was identified in a cloned 5458 bp BamHI–EcoRV DNA fragment and compared to similar genes from other Gram-positive and Gram-negative bacteria described so far.
KeywordsRhodococcus Mycolic Acid Androsterone Steroid Compound Sewage Sludge Sample
We thank the DSMZ (Braunschweig, Germany) for technical support. L. Fernández de las Heras and E. García Fernández are in receipt of scholarships from the Complutense University of Madrid and from the Spanish Ministry of Education and Science, respectively. O. Drzyzga is contracted by the Spanish Ministry of Education and Science in the programme “Ramón y Cajal” (co-financed by the European Social Fund). This work was supported by grants from the Spanish Ministry of Education and Science in the project BFU2006-15214-C03-02.
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