ISOLATION OF A UNIQUE BENZOTHIOPHENE-DESULFURIZING BACTERIUM, GORDONASP. STRAIN-213E (NCIMB-40816), AND CHARACTERIZATION OF THE DESULFURIZATION PATHWAY

Gordona sp. strain 213E (NCIMB 40816) grew in pure culture in a minera l salts medium containing fructose as a source of carbon and energy, a nd benzothiophene (BTH) as the sole source of sulphur. During growth a phenolic compound accumulated, as indicated by the production of a bl ue colour an addition of Gibb's reagent. Therefore this pathway is ana logous to the dibenzothiophene (DBT) desulphurization pathway of Rhodo coccus sp. strain IGTS8, in which 2-hydroxybiphenyl accumulates during growth with DBT as the sole sulphur source. Ethyl acetate extraction of the culture medium yielded the metabolites benzothiophene S-oxide ( BTHO), benzothiophene S,S-dioxide (BTHO2), benzo[c][1,2]oxathiin 6-oxi de (BcOTO), 2-(2'-hydroxyphenyl)ethan 1-al (HPEal) and benzofuran (BFU ), The deduced pathway for BTH desulphurization is BTH --> BTHO --> BT HO2 --> HPESi- --> HPEal, HPESi- is (Z)-2-(2'-hydroxyphenyl)ethen l-su lphinate, the stable aqueous-solution form of BcOTO. It was concluded that HPEal was the Gibb's-reagent-reactive phenolic compound which acc umulated in the culture medium of strain 213E during growth, and that the presence of BFU was due to partial condensation of HPEal during th e ethyl acetate extraction procedure. Gordona sp, strain 213E was unab le to grow in a mineral salts medium containing fructose as a source o f carbon and energy and DBT as the sole sulphur source. BTH-desulphuri zation-active cells (grown using BTH as sole sulphur source) were unab le to desulphurize DBT. Likewise Rhodococcus sp, strain IGTS8 was unab le to grow using BTH as the sole sulphur source, and DBT-desulphurizat ion-active cells of strain IGTS8 (grown using DBT as sole sulphur sour ce) were unable to desulphurize BTH. This absence of crossreactivity i s discussed in terms of fundamental differences in the chemistry of th e DBT- and BTH-desulphurization reactions.