Sunday, April 29, 2007

Evidence for the role of zinc as a cofactor for dbt desulfurization enzymes of gordonia alkanivorans strain 1b

L. Alves1, J. Matos1, R. Tenreiro2, and F.M. Gírio1. (1) Biotechnology Department, INETI, Estrada do Paço do Lumiar, 22, 1649-038 Lisboa, Portugal, (2) Centro de Genética e Biologia Molecular and Instituto de Ciência Aplicada e Tecnologia, Universidade de Lisboa, Faculdade de Ciências, Edifício ICAT, Campus da FCUL, Campo Grande, 1749-016 Lisboa, Portugal

Biodesulfurization of fossil fuels may offer an alternative process to obtain more environmental friendly fuels. Gordonia alkanivorans strain 1B is able to convert dibenzothiophene (DBT) to 2-hydroxybiphenyl (2-HBP), the final product of 4S pathway. The composition of the culture medium used to cultivate desulfurizing bacteria is an important factor, because some of the metal ions can be necessary as enzymatic cofactors.
In this work the effect of several metal ions in the growth and DBT desulfurization by G. alkanivorans was studied. From all the metal ions used only the absence of Zinc did affect significantly the cell growth and the desulfurization rate. Increasing the concentration of Zn from 1 to 10 mg L-1, 2-HBP productivity was improved by 17%. The absence of Zn2+ when sulfate was also used as the only sulfur source did not cause any difference in the bacterial growth. Resting cells grown in the presence of Zn2+ presented a 2-HBP specific productivity of 2.29 μmol g-1 (biomass) h-1, 7.6-fold higher than the specific productivity obtained by resting cells grown in the absence of Zn2+ (0.30 μmol  g-1 (biomass) h-1). The results suggest that zinc is an essential metal cofactor for the catalysis of at least one of the enzymes involved in the metabolism of DBT desulfurization by G. alkanivorans strain 1B. In conclusion, the composition of the culture medium used to grow strain 1B must contain Zn2+ in a 10 mg L-1 concentration instead of 0.5 mg L-1 to obtain a higher desulfurization rate.