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

Abstract

Rhodococcus erythropolis KA2-5-1 is one of the best strains for the desulfurization of dibenzothiophene (DBT) via a sulfur-specific pathway in which DBT 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. Compared with glucose or glycerol, ethanol was found to be a preferable carbon source for obtaining a high specific activity (SA) of desulfurization. When the amount of DBT fed was restricted by feeding 2.9 mg-DBT/g-ethanol solution, 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 hand, 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 desulfurization enzymes in R. erythropolis KA2-5-1 grown on ethanol were remarkably higher than when the strain was grown on glucose or glycerol. It was also suggested that NADH, which is produced by the biochemical reaction of NAD with ethanol catalyzed by alcohol dehydrogenase, might contribute to the conversion of FMN to FMNH 2, which is a coenzyme for the activities of desulfurization enzymes.