Construction and Characterization of a New Recombinant Vector to Remove Sulfate Repression of dsz Promoter Transcription in Biodesulfurization of Dibenzothiophene

Abstract

Biodesulfurization (BDS) is an environmentally friendly desulfurizing process with the potential of replacing or adding to the current expensive technologies for sulfur removal from fossil fuels. The BDS, however, still suffers from low biocatalyst activity. One reason is repression of dsz promoter transcription in presence of inorganic sulfate that impedes translation of Dsz enzymes required for desulfurization pathway. One approach to solve this problem is replacing the native promoter with a new promoter that is no longer repressed. In this study, dsz genes from desulfurizing strain Rhodococcus sp. FUM94 was cloned in an alkane responsive promoter, pCom8, and expressed in Escherichia coli BL21 (DE3) as a host. The recombinant was not susceptible to inorganic sulfate in the culture medium. Desulfurizing activity of recombinant strain versus wild type indicated that in a sulfate containing medium, BDS yield of recombinant increased from 16.0% ± 0.9 to 34.0% ± 1.9% when dibenzothiophene (DBT) concentration (dissolved in ethanol) increased from 25 to 100 ppm. Also, 2-hydroxy biphenyl (2-HBP) production rate improved 8.5-fold (from 0.302 ± 0.020 to 2.57 ± 0.14 mmol 2-HBP (kg DCW)-1 h-1) at the same DBT concentration range. This is while no 2-HBP production was detected in FUM94 biphasic reaction. In a sulfate-free medium, wild type strain demonstrated desulfurization activity, but decreasing with the increase of DBT concentration dissolved in n-tetradecane. Whereas, the recombinant strain demonstrated increasing desulfurizing activity in a sulfate-containing high DBT concentration environment. Overall, the result of this molecular manipulation can be considered as a step forward toward commercialization of BDS technology.

Microbial Surfactants: The Next Generation Multifunctional Biomolecules for Applications in the Petroleum Industry and Its Associated Environmental Remediation

“…Finally, HBPS is hydrolyzed into 2-hydroxybiphenyl (HBP) and sulphite by the DszB enzyme [84]. Increased BDS activity can be enhanced by recombinant strains through the manipulation of the Dsz gene [85]. For example, Raheb and Hajipour [86] used an engineered biodesulphurisation biocatalyst ( Pseudomonas aeruginosa ATCC 9027) for the BDS reaction.…”

Biodesulfurization of Dibenzothiophene and Its Alkylated Derivatives in a Two-Phase Bubble Column Bioreactor by Resting Cells of Rhodococcus erythropolis IGTS8

“…At 1.1 mM and 2.6 mM DBT, almost-complete desulfurization was achieved (YBDS, 1mM= 96.7% and YBDS, 2.6 mM = 94%), while at the highest concentration (4.3 mM), approximately 76% of DBT was desulfurized (Figure 8). Khosravinia et al [42] reported that the biodesulfurization efficiency of Rhodococcus FUM94 resting cells decreased from 71.9% to 57.0% when DBT concentration changed from 0.13 to 0.54 mM, respectively. The specific DBT removal rate exhibited its highest value of 8.3 mm DBT/kg DCW/h at 1 mM initial DBT concentration, and remained almost constant after that.…”

“…In the specific biphasic system used, at 1.1 mM DBT, biodesulfurization was almost complete over a 6 h reaction time; at higher initial DBT concentrations, the time required to reach equilibrium increased with the increase in the amount of unreacted DBT. Khosravinia et al [42] reported that the biodesulfurization efficiency of Rhodococcus FUM94 resting cells decreased from 71.9% to 57.0% when DBT concentration changed from 0.13 to 0.54 mM, respectively. The specific DBT removal rate exhibited its highest value of 8.3 mm DBT/kg DCW/h at 1 mM initial DBT concentration, and remained almost constant after that.…”

Microbial Surfactants: The Next Generation Multifunctional Biomolecules for Diverse Applications

“…Finally, the HBPS is hydrolysed into 2hydroxybiphenyl (HBP) and sulphite by the DszB enzyme [84]. Increased BDS activities can be enhanced by recombinant strains through the manipulation of a Dsz gene [85]. For example, Raheb and Hajipour [86] used an engineered biodesulphurisation biocatalyst (Pseudomonas aeruginosa ATCC 9027) for BDS reaction.…”