Metabolic and process engineering for biodesulfurization in Gram-negative bacteria

Abstract

Microbial desulfurization or biodesulfurization (BDS) is an attractive low-cost and environmentally friendly complementary technology to the hydrotreating chemical process based on the potential of certain bacteria to specifically remove sulfur from S-heterocyclic compounds of crude fuels that are recalcitrant to the chemical treatments. The 4S or Dsz sulfur specific pathway for dibenzothiophene (DBT) and alkyl-substituted DBTs, widely used as model S-heterocyclic compounds, has been extensively studied at the physiological, biochemical and genetic levels mainly in Gram-positive bacteria. Nevertheless, several Gram-negative bacteria have been also used in BDS because they are endowed with some properties, e.g., broad metabolic versatility and easy genetic and genomic manipulation, that make them suitable chassis for systems metabolic engineering strategies. A high number of recombinant bacteria, many of which are Pseudomonas strains, have been constructed to overcome the major bottlenecks of the desulfurization process, i.e., expression of the dsz operon, activity of the Dsz enzymes, retro-inhibition of the Dsz pathway, availability of reducing power, uptake-secretion of substrate and intermediates, tolerance to organic solvents and metals, and other host-specific limitations. However, to attain a BDS process with industrial applicability, it is necessary to apply all the knowledge and advances achieved at the genetic and metabolic levels to the process engineering level, i.e., kinetic modelling, scale-up of biphasic systems, enhancing mass transfer rates, biocatalyst separation, etc. The production of high-added value products derived from the organosulfur material present in oil can be regarded also as an economically viable process that has barely begun to be explored.

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

“…At the same conditions, BDS yield of recombinant strain increased from 16.0% ± 0.9 to 34.0% ± 1.9 (DBT dissolved in ethanol). This observation indicates that the tolerance of the modified strain to high DBT concentrations is more than that of wild type as previously reported in the literature ( Martinez et al, 2017 ). This is also a great advantage of the new construct as in real hydrocarbon media at large-scale, concentrations of organosulfur compounds such as DBT are much higher than those examined in this study.…”

“…Nevertheless, fast growth rate of E. coli compared to other strains, low-cost medium and nutrient, well-known genetic trait and extensive research work performed on this strain has made E. coli an appealing tool for genetic engineering studies including dsz genes insertion. Martinez et al (2017) discussed that several gram negative bacteria have been used in BDS because of some metabolic and genetic properties such as metabolic versatility and easy genetic manipulation; but, they did not address mass transfer limitation in gram negative systems that preferably uptake sulfur source from aqueous phase rather than organic phase. Practically, mass transfer limitation is the main cause of low BDS yield since majority of DBT is dissolved in organic phase and only insignificant amount of DBT remains in aqueous phase.…”

A new functional biofilm biocatalyst for the simultaneous removal of dibenzothiophene and quinoline using Rhodococcus rhodochrous and curli amyloid overproducer mutants derived from Cobetia sp. strain MM1IDA2H-1

“…Relative to biological factors, it should be noted that in this mixed biofilm respective metabolism of DBT and QN in R. rhodochrous and mutants are carry on by different pathways were occurrence of metabolic intermediates and culture media could affect the biocatalyst efficiency. DBT in R. rhodochrous is used as the sulfur source (but not as the carbon source) by the non-destructive “4S pathway” that selectively removes the sulfur generating 2-hydroxybiphenyl as toxic end product affecting bacteria with lower growth rate [ 29 , 30 ]. Nevertheless, according to genomic and microbiological evidence Cobetia sp.…”

Synthesis of Morpholine-Based Ionic Liquids for Extractive Desulfurization of Diesel Fuel

“…Unfortunately, HDS is costly since it requires industrial units operating at high temperatures (>300 °C), pressure (3-10 MPa), and volume of hydrogen gas, with expensive catalysts and low energy efficiency (Kaisy, et al, 2016;Jiang et al, 2016;Zaid et al, 2017). Many of these limitations could be solved by developing desulfurization methods involving adsorption (Shah et al, 2016;Mirshra et al, 2017), oxidative desulphurization (Rezvani et al, 2017;Hitam et al, 2018), bio-desulfurization (Martínez et al, 2017;Paixão et al, 2016), microwave assisted desulphurization, ultrasound (Taheri-Shakib et al, 2017;Mozafari and Nasri, 2017), and extractive desulphurization (Safa et al, 2016;Elwan et al, 2017).…”