Characterization of carbon-sulfur bond cleavage by axenic and mixed cultures of Rhodococcus rhodochrous IGTS8

Abstract

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.

Biodesulfurization of Sour Crude Oil

“…Adopting such methods, DBT is evaluated by the Gibbs test in the presence of aromatic hydroxyl group (Sohrabi et al, 2012). Kayser reported, desulfurization activity is indicated by blue color when reacted, producing 2-hydroxy biphenyl (2HBP) as the final product with Gibbs reagent (Kayser, Bielaga-Jones, Jackowski, Odusan, & Kilbane, 1993). Additionally, HPLC is confirmed of its DBT desulfurization ability of microorganism (Fedorak, 1990: Prayuenyong, 2001).…”