Selective and continuous degradation of carbazole contained in petroleum oil by resting cells of Sphingomonas sp CDH-7

Microbial degradation of carbazole (CA), a model of hard-removal heterocycl ic nitrogen compounds contained in petroleum oil, was examined using Sphing omonas sp. CDH-7 isolated from a soil sample by screening for CA-assimilati ng microorganisms. CDH-7 used CA as a sole source of carbon and nitrogen, a nd metabolized CA to ammonia via anthranilic acid as an intermediate produc t. When CDH-7 was cultivated in the medium containing CA at the concentrati on of 500 mg/l (2.99 mM), CA was completely degraded within 50 h. By the re action with the resting cells of CDH-7, 500 mg/l of CA was completely degra ded within 4 h, with 1.64 mM of ammonia accumulated in the reaction mixture . When CA was added at the concentration of 100 mg/l (0.599 mM) periodicall y to the reaction mixture ten times, 925 mg/l (5.54 mM) of CA was degraded within 48 h by the resting cells, and 4.50 mM of ammonia was accumulated in the reaction mixture with a 75.1% molar conversion yield based on total CA added. The resting tells could almost completely degrade CA in a two-liqui d-phase system which consists of water and organic solvent, even in the pre sence of 20% (v/v) isooctane, n-hexane, cyclohexane, and kerosene as a mode l petroleum oil. In the presence of an organic solvent system such as 20% ( v/v) p-xylene, toluene, and heptanol, however, CA degradation yields decrea sed.