The genus Rhodococcus is a unique taxon consisting of microorganisms that exhibit broad metabolic diversity, particularly to hydrophobic compounds such as hydrocarbons, chlorinated phenolics, steroids, lignin, coal, and petroleum. Advances in chemical, numerical, and molecular systematic methods have contributed greatly to the circumspection of the rhodococci, including the development of diagnostic fluoregenic probes for improved biochemical profiling and identification. Bioprocessing systems employing various Rhodococcus strains are operational for industrial and environmental applications. Such applications include production of acrylic acid and acrylamide, steroid conversions, and bioremediation of chlorinated hydrocarbons and phenolics. Progress on the genetic systems of the rhodococci is rather limited, although a number of plasmids, cloning vectors, and DNA transfer systems have been reported recently, such that progress should be rapid. Certain members of the genus Rhodococcus are known pathogens for humans, animals, and plants. Recent trends indicate that rhodococci of animal origin are opportunistic human pathogens, indicating the need for a greatly improved recognition and understanding of the virulence factors associated with the genus Rhodococcus.
The microbial transformation of dibenzothiophene (DBT) is of interest in the potential desulfurization of oil. We isolated three soil Pseudomonas species which oxidized DBT to characteristic water-soluble, sulfur-containing products. Two of our isolates harbored a 55-megadalton plasmid; growth in the presence of novobiocin resulted in both loss of the plasmid and loss of the ability to oxidize DBT. Reintroduction of the plasmid restored the ability to oxidize DBT to water-soluble products. The products resulting from the oxidation of DBT were characterized and included 3-hydroxy-2-formyl benzothiophene, 3-oxo-[3'-hydroxy-thionaphthenyl-(2)-methyleneJ-dihydrothionaphthene, and the hemiacetal and trans forms of 4-[2-(3-hydroxy)-thianaphthenyl]-2oxo-3-butenoic acid. The products of DBT oxidation were inhibitory to cell growth and further DBT oxidation. DBT oxidation in our soil isolates was induced by naphthalene or salicylate and to a much lesser extent by DBT and was repressed by succinate. A variety of sulfur-containing heterocyclic organic compounds have been characterized in coal, coal tars, and crude oils; dibenzothiophene (DBT) and substituted derivatives of DBT represent important components. DBT is representative of a group of heterocyclic compounds which includes thiophene, benzothiophene, the benzonaphthothiophenes, and more complex sulfur-containing polyaromatic hydrocarbons. Reports describing DBT oxidation by Pseudomonas species (7, 10, 11, 16, 16a), Rhizobium and Acinetobacter species (K. A
Membranes were isolated and purified from nutrient broth-yeast extract-and hexadecane-grown cells of Acinetobacter sp. strain HO1-N. Two membrane fractions were isolated from nutrient broth-yeast extract-grown cells, the cytoplasmic membrane and the outer membrane. In addition to these two membrane fractions, a unique membrane fraction was isolated from hexadecane-grown cells (band 1) and characterized as a lipid-rich, low-density membrane containing high concentrations of hexadecane. The outer membrane preparations of Acinetobacter, obtained from nutrient broth-yeast extract-and hexadecanegrown cells, exhibited a low ratio of lipid phosphorus to protein and contained phospholipase activity and 2-keto-3-deoxyoctulosonic acid. Phosphatidic acid cytidyltransferase, adenosine triphosphatase, and reduced nicotinamide adenine dinucleotide oxidase were recovered almost exclusively in the cytoplasmic membrane fractions. The cytoplasmic membrane fractions contained 20 to 25 polypeptide species on sodium dodecyl sulfate-polyacrylamide gels, and the outer membrane fractions contained 15 to 20 polypeptide species. A major polypeptide species with an apparent molecular weight of approximately 42,000 to 44,000 was found for all outer membrane fractions. The buoyant densities of the cytoplasmic membrane fractions and the outer membrane fractions were closely similar, necessitating their separation by differential centrifugation. Band 1 of hexadecane-grown cells had a ratio of lipid phosphorus to protein that was almost twice that of the cytoplasmic membrane and a correspondingly low buoyant density (1.086 g/cm3). Enzyme activities associated with band 1 were identical to those associated with the cytoplasmic membrane. The electrophoretic banding pattern of band 1 was essentially identical to the banding pattern of the cytoplasmic membrane. The phospholipid and neutral lipid compositions of the isolated membrane fractions were determined as qualitatively similar, with significant quantitative differences. The ultrastructure characteristics of the respective membrane fractions were examined by the negative-stain technique.
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