Genetics Engineering for Removal of Sulfur and Nitrogen from Fuel Heterocycles
Some heteroaromatic compounds, such as S- and N-heterocycles, are among the most toxic and recalcitrant contaminants of crude fuels, and may cause serious environmental (acid precipitation) and industrial (catalysts poisoning) problems. Dibenzothiophene (DBT) and carbazole are widely used as model compounds for S- and N-heterocycles, respectively. Different biochemical pathways for the degradation of these heterocycles have been described in a wide variety of microorganisms, and some of the corresponding catabolic gene clusters were characterized. Whereas a sulfur-specific pathway for DBT biodesulfurization (dsz pathway) has been extensively studied at the physiological, biochemical and genetic levels, a natural pathway for nitrogen-specific removal (biodenitrogenization) has not been yet described. Despite the fact an efficient DBT biodesulfurization depends on the expression and activity of the dsz gene products, host cell contributions also play a pivotal role in achieving the higher activities needed for developing a commercially viable process. A large number of recombinant bacteria have been engineered to overcome the major bottlenecks of the desulfurization process, and the efficient combination of carbazole degradation and DBT desulfurization in a single biocatalyst has been accomplished. The increased use of high-throughput omic techniques, as well as systems biology approaches, will contribute significantly to unravel the intricate regulatory and metabolic networks that govern the degradation of heteroaromatic compounds. These studies will pave the way for further metabolic flux modeling, and for the rational design of synthetic metabolic pathways for upgrading large volumes of fossil fuels – one of the greatest challenges addressed currently by biotechnology.
KeywordsHeteroaromatic Compound Flavin Reductase Desulfurization Activity Carbazole Degradation Desulfurization Pathway
Work in our laboratory was supported by grants from the Comisión Interministerial de Ciencia y Tecnología (GEN2006-27750-C5-3-E, BIO2006-05957, BFU2006-15214-CO3-01, MMA-PR21/06-039/2006/3-11.2, CSD2007-00005) and Comunidad Autónoma de Madrid (P-AMB-259-0505).
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