Carbazole Metabolism by Pseudomonads

Crude oil is a heterogeneous mixture of organic molecules, including alkanes and aromatics, as well as sulfur-, nitrogen-, and oxygen-containing heteroaromatic compounds. The nitrogen-containing compounds found in crude oil can be divided into two classes: “nonbasic” molecules, including pyrroles and indoles, and “basic” molecules, including derivatives of pyridine and quinolines. The total nitrogen content of crude oil averages around 0.3%, of which nonbasic compounds comprise approximately 70–75%. Nonbasic nitrogen-containing heteroaromatics are predominantly mixed alkyl derivatives of carbazole. In contrast, coal-tar creosote is a mixture of 150 to 200 different compounds, of which approximately 85% are polycyclic aromatic hydrocarbons, 10% are phenolic compounds, and 5% are heterocyclic compounds. In the past, creosote was used extensively as a wood preservative on railroad ties, telephone poles, and fence posts. Additionally, creosote is an undesired by-product of coal gasification, and has been sold for asphalt production or stored in underground tanks. Carbazole is the major nitrogen heteroaromatic in coal-tar creosote and is one of the 13 most common heterocyclic compounds in creosote.