Genetic analysis of benzothiophene biodesulfurization pathway of Gordonia terrae strain C-6

Abstract

Sulfur can be removed from benzothiophene (BT) by some bacteria without breaking carbon-carbon bonds. However, a clear mechanism for BT desulfurization and its genetic components have not been reported in literatures so far. In this study, we used comparative transcriptomics to study differential expression of genes in Gordonia terrae C-6 cultured with BT or sodium sulfate as the sole source of sulfur. We found that 135 genes were up-regulated with BT relative to sodium sulfate as the sole sulfur source. Many of these genes encode flavin-dependent monooxygenases, alkane sulfonate monooxygenases and desulfinase, which perform similar functions to those involved in the 4S pathway of dibenzothiophene (DBT) biodesulfurization. Three of the genes were found to be located in the same operon, designated bdsABC. Cell extracts of pET28a-bdsABC transfected E. coli Rosetta (DE3) converted BT to a phenolic compound, identified as o-hydroxystyrene. These results advance our understanding of enzymes involved in the BT biodesulfurization pathway.

Figure 1. The proposed BT biodesulfurization pathway for Sinorhizobium sp. KT55 (a) and Gordonia sp. 213E (b).

(A) benzothiophene; (B) benzothiophene S-oxide; (C) benzothiophene S,S-dioxide; (D) benzo[c][l,2]oxathiin S-oxide; (E) o-hydroxystyrene; (F) 2-(2’-hydroxypheny1)ethan-1-al; (G) benzo[c][1,2]oxathiin S,S-dioxide.

Figure 2. Biodesulfurization of BT during growth of G. terrae strain C-6.

Strain C-6 was cultured in BSM_S- medium with 0.3mM BT as the sole source of sulfur. Black triangles, BT in the culture inoculating with strain C-6; black diamonds, BT in the culture without inoculating with strain C-6; black circles, bacterial growth; black squares, final product of BT biodesulfurization.

Figure 3. Differentially expressed genes of strain C-6 cultured with different sulfur sources.

Red dots indicate differentially expressed genes. Black-colored dots were not considered as significantly differentially expressed. The Y-axis shows the fold-change values between BT and sodium sulfate as sulfur sourcebased on a log₂ scale. The X-axis shows the average count of reads per million reads based on a log₂ scale.

Figure 4. The proposed metabolism of BT for G. terrae strain C-6.