Biodegradation of carbazole by Ralstonia sp RJGII.123 isolated from a hydrocarbon contaminated soil

The use of microorganisms for bioremediation of contaminated soils may be e nhanced with an understanding of the pathways involved in their degradation of hazardous compounds. Ralstonia sp. strain RJGII.123 was isolated from s oil located at a former coal gasification plant, based on its ability to mi neralize carbazole, a three-ring N-heterocyclic pollutant. Experiments were carried out with strain RJGII.123 and C-14-carbazole (2 mg/L and 500 mg/L) as the sole organic carbon source. At 15 days, 80% of the 2 mg/L carbazole was recovered as CO2, and < 1% remained as undegraded carbazole, while 24% of the 500 mg/L carbazole was recovered as CO2 and similar to 70% remained as undegraded carbazole. Several stable intermediates were formed during t his time. These intermediates were separated by high performance liquid chr omatography (HPLC) and were characterized using high resolution mass spectr oscopy (HR-MS) and gas chromatography - mass spectroscopy (GC-MS). At least 10 ring cleavage products of carbazole degradation were identified; four o f these were confirmed as anthranilic acid, indole-2-carboxylic acid, indol e-3-carboxylic acid, and (1H)-4-quinolinone by comparison with standards. T hese data indicate that strain RJGII.123 shares aspects of carbazole degrad ation with previously described Pseudomonas spp., and may be useful in faci litating the bioremediation of NHA from contaminated soils.