Growth assays reveal that Rhodococcus rhodochrous IGTSS uses a wide range of organosulphur compounds as the sole source of sulphur, yet none of the compounds serve as carbon sources. Compounds that are utilized include thiophenes, sulphides, disulphides, mercaptans, sulphoxides, and sulphones. A convenient spectrophotometric assay (Gibbs assay), based on the chromogenic reaction of 2,6-dichloroquinone-4-chloroimide with aromatic hydroxyl groups, was developed and used in conjunction with GC/MS analyses to examine the kinetics of dibenzothiophene metabolism by axenic and mixed cell cultures of Rhodococcus rhodochrous IGTSS. The desulphurization trait is expressed at increasing levels during the exponential phase of growth and then declines in stationary-phase cells. Mixtures of streptomycin-resistant Rhodococcus rhodochrous IGTSS and Enterobacter cloacae (an organism incapable of cleaving carbon-sulphur bonds in relevant test compounds) were prepared in ratios that varied over six orders of magnitude. Growth studies revealed that E. cloacae was able to gain access to sulphur liberated from organosulphur compounds by IGTSS ; however, cell-to-cell contact appears to be required. These experiments also indicate that the desulphurization activity, on a per cell basis, is higher in mixed cultures than in axenic cultures.

Rhodococcus rhodochrous IGTS8 (ATCC 53968) was shown to be capable of utilizing 2-chloroethyl ethyl sulphide (CEES) as the sole source of sulphur for microbial growth. 2-Chloroethanol and a compound tentatively identified as 2-chloroethanesulfinic acid have been detected as metabolites. This demonstrates that carbon-sulphur bonds were cleaved in CEES prior to hydrolysis of the chlorine atom. These data indicate that Rhodococcus rhodochrous IGTSS may be useful for the biodetoxification of the chemical warfare agent mustard (2,2' dichlorodiethyl sulphide).

Growth assays reveal that Rhodococcus rhodochrous IGTS8 can utilize a wide range of organosulfur compounds as the sole source of sulfur. Compounds that are utilized include thiophenes, sulfides, disulfides, mercaptans, sulfoxides, and sulfones. None of the organosulfur compounds tested can serve as a carbon source. A convenient spectrophotometric assay (Gibbs assay) based on the chromogenic reaction of 2,6dichloroquinone-4-chloroimide with aromatic hydroxyl groups was developed and used in conjunction with GC/MS analyses to examine the kinetics of carbon-sulfur bond cleavage by axenic and mixed cell cultures of Rhododcoccx rhodochrous IGTS8. The desulfurization trait is expressed at uniform levels during the mid-exponential phase, reaches a maximum during idiophase, and then declines in stationary-phase cells. Desulfurization rate3 for dibenzothiophene (DBT) range from 8 to 15 ,uM of DBT/10 cells/hour. Mixtures of genetically marked Rhodococcus rhodochrous IGTS8 and an organism incapable of cleaving carbon-sulfur bonds in relevant test compounds, Enterobacter cloacae, were prepared in ratios that varied over six orders of magnitude. Growth studies revealed that Enterobacter cloacae was able to gain access to sulfur liberated from organosulfur compounds by IGTS8; however, cellto-cell contact was required. These data also indicate that the desulfurization activity of IGTS8 cells in mixed cultures may be as much as 200-fold higher than in axenic cultures.