Increase in desulfurization activity of Rhodococcus erythropolis KA2-5-1 using ethanol feeding

Rhodococcus erythropolis KA2-5-1 is one of the best strains for the desulfu rization of dibenzothiophene (DBT) via a sulfur-specific pathway in which D BT is converted to the end product, 2-hydroxybiphenyl, by releasing sulfite via DBT-sulfone and 2-(2'-hydroxyphenyl) benzene sulphinate. The objective of this research is to develop a culture method in order to attain a high cell density with a high level of specific desulfurization activity. Compar ed with glucose or glycerol, ethanol was found to be a preferable carbon so urce for obtaining a high specific activity (SA) of desulfurization. When t he amount of DBT fed was restricted by feeding 2.9 mg-DBT/g-ethanol solutio n, the maximum SA and final cell concentration were 135.5 (mmol-2HBP/kg-dry cell weight.h) and 37 (g-dry cell weight/l), respectively. On the other ha nd, when glucose or glycerol was used as a carbon source, the SA was lower than 50 (mM-2HBP/kg-dry cell weight.h) and the final cell concentration was also lower than 27 (g-dry cell weight/l). The activities of the desulfuriz ation enzymes in R. erythropolis KA2-5-1 grown on ethanol were remarkably h igher than when the strain was grown on glucose or glycerol. It was also su ggested that NADH, which is produced by the biochemical reaction of NAD wit h ethanol catalyzed by alcohol dehydrogenase, might contribute to the conve rsion of FMN to FMNH2, which is a coenzyme for the activities of desulfuriz ation enzymes.