Biotechnology of desulfurization of diesel: prospects and challenges

Genomic analysis and biodesulfurization potential of a new carbon-sulfur bond cleaving Tsukamurella sp. 3OW

Direct combustion of sulfur-enriched liquid fuel oil causes sulfur oxide emission, which is one of the main contributors to air pollution. Biodesulfurization is a promising and eco-friendly method to desulfurize a wide range of thiophenic compounds present in fuel oil. Previously, numerous bacterial strains from genera such as Rhodococcus, Corynebacterium, Gordonia, Nocardia, Mycobacterium, Mycolicibacterium, Paenibacillus, Shewanella, Sphingomonas, Halothiobacillus, and Bacillus have been reported to be capable of desulfurizing model thiophenic compounds or fossil fuels. In the present study, we report a new desulfurizing bacterium, Tsukamurella sp. 3OW, capable of desulfurization of dibenzothiophene through the carbon-sulfur bond cleavage 4S pathway. The bacterium showed a high affinity for the hydrocarbon phase and broad substrate specificity towards various thiophenic compounds. The overall genome-related index analysis revealed that the bacterium is closely related to Tsukamurella paurometabola species. The genomic pool of strain 3OW contains 57 genes related to sulfur metabolism, including the key dszABC genes responsible for dibenzothiophene desulfurization. The DBT-adapted cells of the strain 3OW displayed significant resilience and viability in elevated concentrations of crude oil. The bacterium showed a 19 and 37% reduction in the total sulfur present in crude and diesel oil, respectively. Furthermore, FTIR analysis indicates that the oil's overall chemistry remained unaltered following biodesulfurization. This study implies that Tsukamurella paurometabola species, previously undocumented in the context of biodesulfurization, has good potential for application in the biodesulfurization of petroleum oils.

DszA Catalyzes C-S Bond Cleavage through N5-Hydroperoxyl Formation

Due to its detrimental impact on human health and the environment, regulations demand ultralow sulfur levels on fossil fuels, in particular in diesel. However, current desulfurization techniques are expensive and cannot efficiently remove heteroaromatic sulfur compounds, which are abundant in crude oil and concentrate in the diesel fraction after distillation. Biodesulfurization via the four enzymes of the metabolic 4S pathway of the bacterium Rhodococcus erythropolis (DszA-D) is a possible solution. However, the 4S pathway needs to operate at least 500 times faster for industrial applicability, a goal currently pursued through enzyme engineering. In this work, we unveil the catalytic mechanism of the flavin monooxygenase DszA. Surprisingly, we found that this enzyme follows a recently proposed atypical mechanism that passes through the formation of an N5OOH intermediate at the re side of the cofactor, aided by a well-defined, predominantly hydrophobic O2 pocket. Besides clarifying the unusual chemical mechanism of the complex DszA enzyme, with obvious implications for understanding the puzzling chemistry of flavin-mediated catalysis, the result is crucial for the rational engineering of DszA, contributing to making biodesulfurization attractive for the oil refining industry.

Cooperation among nitrifying microorganisms promotes the irreversible biotransformation of sulfamonomethoxine

Ammonia-oxidizing microorganisms, including AOA (ammonia-oxidizing archaea), AOB (ammonia-oxidizing bacteria), and Comammox (complete ammonia oxidization) Nitrospira, have been reported to possess the capability for the biotransformation of sulfonamide antibiotics. However, given that nitrifying microorganisms coexist and operate as communities in the nitrification process, it is surprising that there is a scarcity of studies investigating how their interactions would affect the biotransformation of sulfonamide antibiotics. This study aims to investigate the sulfamonomethoxine (SMM) removal efficiency and mechanisms among pure cultures of phylogenetically distinct nitrifiers and their combinations. Our findings revealed that AOA demonstrated the highest SMM removal efficiency and rate among the pure cultures, followed by Comammox Nitrospira, NOB, and AOB. However, the biotransformation of SMM by AOA N. gargensis is reversible, and the removal efficiency significantly decreased from 63.84 % at 167 h to 26.41 % at 807 h. On the contrary, the co-culture of AOA and NOB demonstrated enhanced and irreversible SMM removal efficiency compared to AOA alone. Furthermore, the presence of NOB altered the SMM biotransformation of AOA by metabolizing TP202 differently, possibly resulting from reduced nitrite accumulation. This study offers novel insights into the potential application of nitrifying communities for the removal of sulfonamide antibiotics (SAs) in engineered ecosystems.

Simulated-sunlight enhances membrane aerated biofilm reactor performance in sulfamethoxazole removal and antibiotic resistance genes reduction

Membrane aerated biofilm reactors (MABRs) can be used to treat domestic wastewater containing sulfamethoxazole (SMX) because of their favorable performance in the treatment of refractory pollutants. However, biologics are generally subjected to antibiotics stress, which induces the production of antibiotic resistance genes (ARGs). In this study, a simulated-sunlight assisted MABR (L-MABR) was used to promote SMX removal and reduce ARGs production. The SMX removal efficiency of the l-MABR system was 9.62 % superior to that of the MABR system (83.13 %). In contrast from MABR, in the l-MABR, only 28.75 % of SMX was removed through microbial activity because functional bacteria were inactivated through radiation by simulated sunlight. In addition, photolysis (64.61 %) dominated SMX removal, and the best performing indirect photolysis process was the excited state of effluent organic matters (3EfOMs*). Through photolysis, ultraviolet (UV) and reactive oxygen species (ROS) enriched the SMX removal route, resulting in the SMX removal pathway in the l-MABR no longer being limited by enzyme catalysis. More importantly, because of the inactivation of functional bacteria, whether in the effluent or biofilm, the copy number of ARGs in the l-MABR was 1-3 orders of magnitude lower than that in the MABR. Our study demonstrates the feasibility of utilizing simulated-sunlight to enhance the antibiotic removal efficiency while reducing ARG production, thus providing a novel idea for the removal of antibiotics from wastewater.

Mapping the knowledge domain of microbial desulfurization application in fuels and ores for sustainable industry

Direct application of high-sulfur fuels and ores can cause environmental pollution (such as air pollution and acid rain) and, in serious cases, endanger human health and contribute to property damage. In the background of preserving the environment, microbial desulfurization technologies for high-sulfur fuels and ores are rapidly developed. This paper aims to reveal the progress of microbial desulfurization research on fuels and ores using bibliometric analysis. 910 publications on microbial desulfurization of fuels and ores from web core databases were collected in this work, spanning 39 years. Through 910 retrieved documents, collaborative networks of authors, institutions and countries were mapped by this work, the sources of highly cited articles and cited documents were statistically analyzed, and keyword development from different perspectives was discussed. The results of the study provide a reference for microbial desulfurization research and benefit environmental protection and energy green applications.

Sulfamethoxazole degradation by Aeromonas caviae and co-metabolism by the mixed bacteria

Sulfamethoxazole (SMX) is a frequently detected antibiotic in the environment and has attracted much attention. Aeromonas caviae strain GLB-10 was isolated, which could degrade SMX to Aniline and 3-Amino-5-methylisoxazole. Compared to the single bacteria, the mixed bacteria including stain GLB-10, Vibrio diabolicus strain L2-2, Zobellella taiwanensis, Microbacterium testaceum, Methylobacterium, etc, had an ultrahigh degradation efficiency to SMX, with 250 mg/L SMX being degraded in 3 days. In addition to bioproducts of single bacteria, SMX bioproducts by the mixed bacteria also included acetanilide and hydroquinone which were not detected in the single bacteria. The SMX degradation mechanism of the mixed bacteria was more complicated including acetylation, sulfur reduction 4S pathway, and ipso-hydrolysis. The molecular mechanism of the mixed bacteria degrading SMX was also investigated, revealing that the resistance mechanism related to protein outer membrane protein and catalase peroxidase were overexpressed, meanwhile, 6-hydroxynicotinate 3-monooxygenase and ammonia monooxygenase might be the key proteins in SMX degradation. The mixed bacteria could efficiently degrade SMX in different real environments including tap water, river water, artificial lake water, estuary, and, marine water, and have very great research value in bacterial co-metabolism and biodegradation of sulfonamides antibiotics in the environment.

Bacterial Biological Factories Intended for the Desulfurization of Petroleum Products in Refineries

The removal of sulfur by deep hydrodesulfurization is expensive and environmentally unfriendly. Additionally, sulfur is not separated completely from heterocyclic poly-aromatic compounds. In nature, several microorganisms (Rhodococcus erythropolis IGTS8, Gordonia sp., Bacillus sp., Mycobacterium sp., Paenibacillus sp. A11-2 etc.) have been reported to remove sulfur from petroleum fractions. All these microbes remove sulfur from recalcitrant organosulfur compounds via the 4S pathway, showing potential for some organosulfur compounds only. Activity up to 100 µM/g dry cell weights is needed to meet the current demand for desulfurization. The present review describes the desulfurization capability of various microorganisms acting on several kinds of sulfur sources. Genetic engineering approaches on Gordonia sp. and other species have revealed a variety of good substrate ranges of desulfurization, both for aliphatic and aromatic organosulfur compounds. Whole genome sequence analysis and 4S pathway inhibition by a pTeR group inhibitor have also been discussed. Now, emphasis is being placed on how to commercialize the microbes for industrial-level applications by incorporating biodesulfurization into hydrodesulfurization systems. Thus, this review summarizes the potentialities of microbes for desulfurization of petroleum. The information included in this review could be useful for researchers as well as the economical commercialization of bacteria in petroleum industries.

Comparative Genomic Analysis of the Hydrocarbon-Oxidizing Dibenzothiophene-Desulfurizing Gordonia Strains

A number of actinobacteria of the genus Gordonia are able to use dibenzothiophene (DBT) and its derivatives as the only source of sulfur, which makes them promising agents for the process of oil biodesulfurization. Actinobacteria assimilate sulfur from condensed thiophenes without breaking the carbon-carbon bonds, using the 4S pathway encoded by the dszABC operon-like structure. The genome of the new dibenzothiophene-degrading hydrocarbon-oxidizing bacterial strain Gordonia amicalis 6-1 was completely sequenced and the genes potentially involved in the pathways of DBT desulfurization, oxidation of alkanes and aromatic compounds, as well as in the osmoprotectant metabolism in strain 6-1 and other members of the genus Gordonia, were analyzed. The genome of G. amicalis strain 6-1 consists of a 5,105,798-bp circular chromosome (67.3% GC content) and an 86,621-bp circular plasmid, pCP86 (65.4% GC content). This paper presents a comparative bioinformatic analysis of complete genomes of strain 6-1 and dibenzothiophene-degrading Gordonia strains 1D and 135 that do not have the dsz operon. The assumption is made about the participation in this process of the region containing the sfnB gene. Genomic analysis supported the results of phenomenological studies of Gordonia strains and the possibility of their application in the bioremediation of oil-contaminated environments and in the purification of oil equipment from oil and asphalt-resin-paraffin deposits.

Biodesulfurization of Dibenzothiophene by Decorating Rhodococcus erythropolis IGTS8 Using Montmorillonite/Graphitic Carbon Nitride

Fossil fuels are the main sources of human energy, but their combustion releases toxic compounds of sulfur oxide. In the oil industry, using the optimal methods to eliminate sulfur compounds from fossil fuels is a very important issue. In this study, the performance of montmorillonite/graphitic carbon nitride (a new hybrid nanostructure) in increasing the biodesulfurization activity of Rhodococcus erythropolis IGTS8 was investigated. X-ray diffraction, Fourier-transform infrared spectroscopy, field emission scanning electron microscopy and transmission electron microscopy were used for the characterization of the nanoparticles. The effective factors in this process were determined. Optimum conditions for microorganisms were designed using the Design Expert software. Experiments were performed in a flask. The results indicated that the biodesulfurization activity of a microorganism in the presence of the nanostructure increases by 52%. In addition, in the presence of the nanostructure, the effective factors are: 1. concentration of the nanostructure; 2. concentration of sulfur; 3. cell concentration. In the absence of the nanostructure, the only effective factor is the concentration of sulfur. Through analysis of variance, the proposed models were presented to determine the concentration of the 2-hydroxy biphenyl produced by the microorganisms (biodesulfurization activity) in the presence and absence of the nanostructure. The proposed models were highly acceptable and consistent with experimental data. The results of a Gibbs assay showed that the biodesulfurization efficiency of in the presence of the nanostructure was increased by about 52%, which is a very satisfactory result. The biodesulfurization activity of decorated cells in a bioreactor showed a significant increase compared with nondecorated cells. Almost a two-fold improvement in biodesulfurization activity was obtained for decorated cells compared with free cells.

Enhancing biodesulfurization by engineering a synthetic dibenzothiophene mineralization pathway

A synthetic dibenzothiophene (DBT) mineralization pathway has been engineered in recombinant cells of Pseudomonas azelaica Aramco J strain for its use in biodesulfurization of thiophenic compounds and crude oil. This functional pathway consists of a combination of a recombinant 4S pathway responsible for the conversion of DBT into 2-hydroxybiphenyl (2HBP) and a 2HBP mineralization pathway that is naturally present in the parental P. azelaica Aramco J strain. This novel approach allows overcoming one of the major bottlenecks of the biodesulfurization process, i.e., the feedback inhibitory effect of 2HBP on the 4S pathway enzymes. Resting cells-based biodesulfurization assays using DBT as a sulfur source showed that the 2HBP generated from the 4S pathway is subsequently metabolized by the cell, yielding an increase of 100% in DBT removal with respect to previously optimized Pseudomonas putida biodesulfurizing strains. Moreover, the recombinant P. azelaica Aramco J strain was able to use DBT as a carbon source, representing the best characterized biocatalyst harboring a DBT mineralization pathway and constituting a suitable candidate to develop future bioremediation/bioconversion strategies for oil-contaminated sites.

Interplay between Sulfur Assimilation and Biodesulfurization Activity in Rhodococcus qingshengii IGTS8: Insights into a Regulatory Role of the Reverse Transsulfuration Pathway

Biodesulfurization is a process that selectively removes sulfur from dibenzothiophene and its derivatives. Several natural biocatalysts harboring the highly conserved desulfurization operon dszABC, which is significantly repressed by methionine, cysteine, and inorganic sulfate, have been isolated. However, the available information on the metabolic regulation of gene expression is still limited. In this study, scarless knockouts of the reverse transsulfuration pathway enzyme genes cbs and metB were constructed in the desulfurizing strain Rhodococcus sp. strain IGTS8. We provide sequence analyses and report the enzymes' involvement in the sulfate- and methionine-dependent repression of biodesulfurization activity. Sulfate addition in the bacterial culture did not repress the desulfurization activity of the Δcbs strain, whereas deletion of metB promoted a significant biodesulfurization activity for sulfate-based growth and an even higher desulfurization activity for methionine-grown cells. In contrast, growth on cysteine completely repressed the desulfurization activity of all strains. Transcript level comparison uncovered a positive effect of cbs and metB gene deletions on dsz gene expression in the presence of sulfate and methionine, but not cysteine, offering insights into a critical role of cystathionine β-synthase (CβS) and MetB in desulfurization activity regulation. IMPORTANCE Precise genome editing of the model biocatalyst Rhodococcus qingshengii IGTS8 was performed for the first time, more than 3 decades after its initial discovery. We thus gained insight into the regulation of dsz gene expression and biocatalyst activity, depending on the presence of two reverse transsulfuration enzymes, CβS and MetB. Moreover, we observed an enhancement of biodesulfurization capability in the presence of otherwise repressive sulfur sources, such as sulfate and l-methionine. The interconnection of cellular sulfur assimilation strategies was revealed and validated.

Mechanistic Understanding of Gordonia sp. in Biodesulfurization of Organosulfur Compounds

Although conventional oil refining process like hydrodesulfurization (HDS) is capable of removing sulfur compounds present in crude oil, it cannot desulfurize recalcitrant organosulfur compounds such as dibenzothiophenes (DBTs), benzothiophenes (BTs), etc. Biodesulfurization (BDS) is a process of selective removal of sulfur moieties from DBT or BT by desulfurizing microbes. Therefore, BDS can be used as a complementary and economically feasible technology to achieve deep desulfurization of crude oil without affecting the calorific value. In the recent past, members of biodesulfurizing actinomycete genus Gordonia, isolated from versatile environments like soil, activated sludge, human beings etc. have been greatly exploited in the field of petroleum refining technology. The bacterium Gordonia sp. is slightly acid-fast and has been used for unconventional but potential oil refining processes like BDS in petroleum refineries. Gordonia sp. is unique in a way, that it can desulfurize both aliphatic and aromatic organosulfurs without affecting the calorific value of hydrocarbon molecules. Till date, approximately six different species and nineteen strains of the genus Gordonia have been recognized for BDS activity. Various factors such as enzyme specificity, availability of essential cofactors, feedback inhibition, toxicity of organic pollutants and the oil-water separations limit the desulfurization rate of microbial biocatalyst and influence its commercial applications. The current review selectively highlights the role of this versatile genus in removing sulfur from fossil fuels, mechanisms and future prospects on sustainable environment friendly technologies for crude oil refining.

Preparation of magnetic urchin-like NiCo2O4 powders by hydrothermal synthesis for catalytic oxidative desulfurization

The bundle-like NiCo2O4 powder was synthesized using hydrothermal synthesis and high-temperature calcination method and, as catalyst, NiCo2O4 powder was utilized to activate peroxymonosulfate for removing dibenzothiophene from fuel oil.

Non-hydrogen processes for simultaneous desulfurization and denitrogenation of light petroleum fuels-an elaborative review

The removal of sulfur- and nitrogen-containing compounds present in petroleum fractions is necessary to meet the stringent environmental regulations and to prevent the environment and humanity from the threats they pose. Conventional hydro-desulfurization and hydro-denitrogenation processes have evolved significantly over the past decade but are limited due to severe operating conditions and inefficiency in removing nitrogen-containing compounds. On the contrary, unconventional non-hydrogen methods for refining of crude oils are beneficial in terms of mild operating conditions and are efficient for eradicating both sulfur- and nitrogen-containing compounds. Despite being efficient for both sulfur and nitrogen-containing compounds, these techniques suffer due to the hindrance posed by the competitive nature of nitrogen-containing compounds. Thus, it is recommended to develop techniques that can remove both the compounds simultaneously and efficiently. Techniques for simultaneous removal of those compounds can also be expected to reduce the number of unit operations required during refining and can be energy-efficient as well. This elaborative review summarizes the developments done in this field in the past two decades. To improve the understanding of the scientific community towards the feasibility of simultaneous desulfurization and denitrogenation processes, the crucial parameters for efficient desulfurization-denitrogenation processes are also discussed. This review can be expected to encourage the scientific community to search for more economical, energy-efficient, and commercializable pathways for desulfurization-denitrogenation of petroleum oil.

Nanocatalysts for Oxidative Desulfurization of Liquid Fuel: Modern Solutions and the Perspectives of Application in Hybrid Chemical-Biocatalytic Processes

In this paper, the current advantages and disadvantages of using metal-containing nanocatalysts (NCs) for deep chemical oxidative desulfurization (ODS) of liquid fuels are reviewed. A similar analysis is performed for the oxidative biodesulfurization of oil along the 4S-pathway, catalyzed by various aerobic bacterial cells of microorganisms. The preferences of using NCs for the oxidation of organic sulfur-containing compounds in various oil fractions seem obvious. The text discusses the development of new chemical and biocatalytic approaches to ODS, including the use of both heterogeneous NCs and anaerobic microbial biocatalysts that catalyze the reduction of chemically oxidized sulfur-containing compounds in the framework of methanogenesis. The addition of anaerobic biocatalytic stages to the ODS of liquid fuel based on NCs leads to the emergence of hybrid technologies that improve both the environmental characteristics and the economic efficiency of the overall process. The bioconversion of sulfur-containing extracts from fuels with accompanying hydrocarbon residues into biogas containing valuable components for the implementation of C-1 green chemistry processes, such as CH4, CO2, or H2, looks attractive for the implementation of such a hybrid process.

Microfluidically supported characterization of responses of Rhodococcus erythropolis strains isolated from different soils on Cu-, Ni-, and Co-stress

We present a new methodological approach for the assessment of the susceptibility of Rhodococcus erythropolis strains from specific sampling sites in response to increasing heavy metal concentration (Cu²⁺, Ni²⁺, and Co²⁺) using the droplet-based microfluid technique. All isolates belong to the species R. erythropolis identified by Sanger sequencing of the 16S rRNA. The tiny step-wise variation of metal concentrations from zero to the lower mM range in 500 nL droplets not only provided accurate data for critical metal ion concentrations but also resulted in a detailed visualization of the concentration-dependent response of bacterial growth and autofluorescence activity. As a result, some of the isolates showed similar characteristics in heavy metal tolerance against Cu²⁺, Ni²⁺, and Co²⁺. However, significantly different heavy metal tolerances were found for other strains. Surprisingly, samples from the surface soil of ancient copper mining areas supplied mostly strains with a moderate sensitivity to Cu²⁺, Ni²⁺, and Co²⁺, but in contrast, a soil sample from an excavation site of a medieval city that had been covered for about eight centuries showed an extremely high tolerance against cobalt ion (up to 36 mM). The differences among the strains not only may be regarded as results of adaptation to the different environmental conditions faced by the strains in nature but also seem to be related to ancient human activities and temporal partial decoupling of soil elements from the surface. This investigation confirmed that microfluidic screening offers empirical characterization of properties from same species which has been isolated from sites known to have different human activities in the past.

Characterization and genomic analysis of Gordonia alkanivorans 135, a promising dibenzothiophene-degrading strain

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Strain 135 is first dibenzothiophene-degrading Gordonia with genome fully assembled.

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This is the first strain of Gordonia absorbing thiophene sulfur without dsz genes.

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The strain utilized 45.26 % of dibenzothiophene within 150 h of growth at 26 °C.

Sulfur is the third most abundant element in crude oil. Up to 70 % of sulfur in petroleum is found in the form of dibenzothiophene (DBT) and substituted DBTs. The aim of this work was to study the physiological, biochemical and genetical characteristics of Gordonia alkanivorans 135 capable of using DBT as the sole source of sulfur. The genome of G. alkanivorans 135 consists of a 5,039,827 bp chromosome and a 164,963 bp circular plasmid. We found the absence of dsz operon present in most DBT degrading bacteria, but discovered other genes that are presumably involved in DBT utilization by G. alkanivorans 135. The strain utilized 45.26 % of DBT within 150 h of growth at 26 °C. This is the first strain of Gordonia capable of absorbing thiophene sulfur without the aid of the dsz genes.

Desulphurisation kinetics of thiophenic compound by sulphur oxidizing Klebsiella oxytoca SOB-1

AIMS

The major aims of this study are to determine the capability of sulphur oxidizing bacterium (SOB-1) to desulphurize dibenzothiophene (DBT) and crude oil, detection of the reaction kinetics and identify the proposed pathway of DBT desulphurization.

METHODS AND RESULTS

The isolate was genetically identified based on 16S rRNA gene sequencing as Klebsiella oxytoca and deposited in the Genebank database under the accession number: MT355440. The HPLC analysis of the remaining DBT concentration revealed that, SOB-1 could desulphurize 90% of DBT (0·25 mmol l^-1 ) within 96 h. The maximum production of sulphate ions from the desulphurization of DBT (0·36 mmol l^-1 ) and crude oil (0·4 mmol l^-1 ) could be quantitatively detected after 48 h of incubation at 30°C. The high values of correlation coefficient (R² ) obtained at all studied concentrations; suggested that biodesulfurization kinetics of DBT follows the first-order reaction model. The kinetics studies showed that, DBT may have an inhibitory effect on SOB-1 when the initial concentration exceeded 0·75 mmol l^-1 . The GC-MS analysis exhibited four main metabolites rather than DBT. The most important ones are 2-hydroxybiphenyl (2-HBP) and methoxybiphenyl n(2-MBP).

CONCLUSIONS

Klebsiella oxytoca SOB-1 catalyzes the desulphurization of DBT through 4S pathway and forms four main metabolic products. The release of sulphate ion and formation of 2-HBP indicating the elimination of sulphur group without altering the carbon skeleton of DBT. The bacterial strain could also catalyzes desulphurization of crude oil. The desulphurization kinetics follows the first-order reaction model.

SIGNIFICANCE AND IMPACT OF THE STUDY

Klebsiella oxytoca SOB-1 could be used as a promising industrial and environmental biodesulfurizing agent as it is not affecting carbon skeleton of thiophenic compounds and forming less toxic metabolic product (2-MBP).

Bacterial and enzymatic degradation of poly(cis-1,4-isoprene) rubber: Novel biotechnological applications

Poly(cis-1,4-isoprene) rubber is a highly demanded elastomeric material mainly used for the manufacturing of tires. The end-cycle of rubber-made products is creating serious environmental concern and, therefore, different recycling processes have been proposed. However, the current physical-chemical processes include the use of hazardous chemical solvents, large amounts of energy, and possibly generations of unhealthy micro-plastics. Under this scenario, eco-friendly alternatives are needed and biotechnological rubber treatments are demonstrating huge potential. The cleavage mechanisms and the biochemical pathways for the uptake of poly(cis-1,4-isoprene) rubber have been extensively reported. Likewise, novel bacterial strains able to degrade the polymer have been studied and the involved structural and functional enzymes have been analyzed. Considering the fundamentals, biotechnological approaches have been proposed considering process optimization, cost-effective methods and larger-scale experiments in the search for practical and realistic applications. In this work, the latest research in the rubber biodegradation field is shown and discussed, aiming to analyze the combination of detoxification, devulcanization and polymer-cleavage mechanisms to achieve better degradation yields. The modified superficial structure of rubber materials after biological treatments might be an interesting way to reuse old rubber for re-vulcanization or to find new materials.

Recent Advances in Functionalized Mesoporous Silica Frameworks for Efficient Desulfurization of Fuels

Considerable health and climate benefits arising from the use of low-sulfur fuels has propelled the research on desulfurization of fossil fuels. Ideal fuels are urgently needed and are expected to be ultra-low in sulfur (10-15 ppm), with no greater than 50 ppm sulfur content. Although several sulfur removal techniques are available in refineries and petrochemical units, their high operational costs, complex operational needs, low efficiencies, and higher environmental risks render them unviable and challenging to implement. In recent years, mesoporous silica-based materials have emerged as promising desulfurizing agents, owing to their high porosity, high surface area, and easier functionalization compared to conventional materials. In this review, we report on recent progress in the synthesis and chemistry of new functionalized mesoporous silica materials aiming to lower the sulfur content of fuels. Additionally, we discuss the role of special active sites in these sorbent materials and investigate the formulations capable of encapsulating and trapping the sulfur-based molecules, which are challenging to remove due to their complexity, for example the species present in JP-8 jet fuels.

Investigating the effect of starch/Fe3O4 nanoparticles on biodesulfurization using molecular dynamic simulation

The application of dibenzothiophene (DBT) as a source of energy leads to air pollution. The key solution to overcome this drawback is desulfurization. Magnetic nanoparticles have shown an excellent performance in the desulfurization of dibenzothiophene. In this study, molecular dynamic (MD) simulation was considered for the first time to gain insight about the molecule interactions in the biodesulfurization (BDS) process of DBT using Rhodococcus erythropolis IGTS8, in the presence and absence of starch/magnetic nanoparticles. According to the MD simulation results, the density of the system in the presence of starch/Fe₃O₄ was ascending while in the absence of these nanoparticles, the density was descending. Starch/magnetic nanoparticles caused more rapid equilibrium state in the biodesulfurization process. The energy diagram showed that magnetic nanoparticles decrease the energy fluctuation and increase the difference of non-bounding energy and potential energy (8 times) compared to (BDS) without nanoparticle, which reflects higher bounded energy in the system using starch/magnetic nanoparticles. The height of RDF peak in the presence of starch/Fe₃O₄ was 4 times more than the RDF peak in the absence of nanoparticle. In addition, the nanoparticles decreased the fluctuations around optimal temperature in BDS up to 5% compared to other state.

Investigation of Desulfurization Activity, Reusability, and Viability of Magnetite Coated Bacterial Cells

Background

Magnetic separation using magnetic nanoparticles can be used as a simple method to isolate desulfurizing bacteria from a biphasic oil/water system.

Objectives

Magnetite nanoparticles were applied to coat the surface of Rhodococcus erythropolis IGTS8 and Rhodococcus erythropolis FMF desulfurizing bacterial cells, and the viability and reusability of magnetite-coated bacteria evaluated by using various methods.

Material and Methods

Magnetite nanoparticles were synthesized through a reverse co-precipitation method. Glycine was added during and after the synthesis of magnetite nanoparticles to modify their surface and to stabilize the dispersion of the nanoparticles. The glycine-modified magnetite nanoparticles were immobilized on the surface of both oil-desulfurizing bacterial strains. Reusability of magnetite-coated bacterial cells was evaluated via assessing the desulfurization activity of bacteria via spectrophotometry using Gibb’s assay, after the separation of bacterial cells from 96h-cultures with the application of external magnetic field. In addition, CFU and fluorescence imaging were used to investigate the viability of magnetite-coated and free bacterial cells.

Results

TEM micrographs showed that magnetite nanoparticles have the size approximately 5.35±1.13 nm. Reusability results showed that both magnetite-coated bacterial strains maintain their activity even after 5 × 96h-cycles. The viability results revealed glycine-modified magnetite nanoparticles did not negatively affect the viability of two bacterial strains R. erythropolis IGTS8 and R. erythropolis FMF.

Conclusions

In conclusion, the glycine-modified magnetite nanoparticles have great capacity for immobilization and separation of desulfurizing bacteria from suspension.

Simulation-based protein engineering of R. erythropolis FMN oxidoreductase (DszD)

The sulfur contents of fossil fuels have negative impacts on the environment and human health. The bio-catalytic desulfurization strategies and the biological refinement of fossil fuels are a cost-effective process compared to classical chemistry desulfurization. Rhodococcus erythropolis IGTS8 is able to metabolize the organic sulfur compound by the unique genes cluster (i.e. DszA, B, C and D genes) in the 4S metabolic pathway. The dszD gene codes a key enzyme for sulfur reduction in the gene cluster. In this study, the structure of the DszD enzyme was predicted and then the key residues toward FMN binding were identified which were Thr62, Ser63, Asn77, and Ala79. To investigate the effect of manipulation in key residues on the enzymatic activity of the DszD, different mutations were performed on key residues. The molecular docking simulation showed that A79I and A79N mutants have the lowest binding free energies compared to the wild-type enzyme in binding with FMN substrate. A 50 ns molecular dynamics (MD) simulation performed using GROMACS software. The RMSD and RMSF analysis showed that two mutants are more stable than the wild-type enzyme during MD simulation. The binding free energies between FMN substrate and complexes were calculated and analyzed by the Molecular Mechanics/Poisson-Boltzmann Surface Area (MM-PBSA) method. The experimental results showed that the enzyme activity for the oxidoreductase process toward biodesulfurization increased 1.9 and 2.3 fold for A79I and A79N mutants, respectively.

Biodegradation of dibenzothiophene by efficient Pseudomonas sp. LKY-5 with the production of a biosurfactant

A potent bacterial strain capable of degrading dibenzothiophene (DBT) was isolated and evaluated for its characteristics. The strain, designated as LKY-5, is rod-shaped, gram-negative, and occurs mainly in clusters. It was identified as belonging to the Pseudomonas genus based on the 16S rDNA sequence and phylogenic analysis. Determination of its DBT depletion efficiency by gas chromatography revealed that the isolate was able to completely degrade up to 100 mg L^-1 DBT within 144 h. The pH values, DBT concentrations, and biomasses in the medium varied significantly in the initial 24 h. A biosurfactant produced by LKY-5 was extracted and identified as a di-rhamnolipid with the formula Rha-Rha-C₈-C_8:1 by HPLC-ESI-MS/MS. There were 26 metabolites in the DBT degradation process. Pseudomonas sp. LKY-5 exhibited unusually high DBT degradation efficiency via multiple metabolic pathways. Compared with the reported 4S and Kodama pathways, two more expanded metabolic pathways for the degradation of DBT are proposed. The polycyclic aromatic sulfur heterocycles (PASHs) in diesel, such as C₁-DBT, C₂-DBT, C₃-DBT, 4,6-DMDBT, and 2,4,6-TMDBT, can also be degraded with 28.2-42.3% efficiency. The results showed that LKY-5 is an excellent bacterial candidate for the bioremediation of PASH-contaminated sites and sediments.

An overview of conventional and alternative technologies for the production of ultra-low-sulfur fuels

Environmental concerns have given a great deal of attention for the production of ultra-low-sulfur fuels. The conventional hydrodesulfurization (HDS) process has high operating cost and also encounters difficulty in removing sulfur compound with steric hindrance. Consequently, various research efforts have been made to overcome the limitation of conventional HDS process and exploring the alternative technologies for deep desulfurization. The alternative processes being explored for the production of ultra-low-sulfur content fuel are adsorptive desulfurization (ADS), biodesulfurization (BDS), oxidative desulfurization (ODS), and extractive desulfurization (EDS). The present article provided the comprehensive information on the basic principle, reaction mechanism, workability, advantages, and disadvantages of conventional and alternative technologies. This review article aims to provide valuable insight into the recent advances made in conventional HDS process and alternative techniques. For deep desulfurization of liquid fuels, integration of conventional HDS with an alternative technique is also proposed.

Biomining of iron-containing nanoparticles from coal tailings

Sulfur minerals originating from coal mining represent an important environmental problem. Turning these wastes into value-added by-products can be an interesting alternative. Biotransformation of coal tailings into iron-containing nanoparticles using Rhodococcus erythropolis ATCC 4277 free cells was studied. The influence of culture conditions (stirring rate, biomass concentration, and coal tailings ratio) in the particle size was investigated using a 2³ full factorial design. Statistical analysis revealed that higher concentrations of biomass produced larger sized particles. Conversely, a more intense stirring rate of the culture medium and a higher coal tailings ratio (% w/w) led to the synthesis of smaller particles. Thus, the culture conditions that produced smaller particles (< 50 nm) were 0.5 abs of normalized biomass concentration, 150 rpm of stirring rate, and 2.5% w/w of coal tailings ratio. Composition analyses showed that the biosynthesized nanoparticles are formed by iron sulfate. Conversion ratio of the coal tailings into iron-containing nanoparticles reached 19%. The proposed biosynthesis process, using R. erythropolis ATCC 4277 free cells, seems to be a new and environmentally friendly alternative for sulfur minerals reuse.

Functional and mechanistic characterization of an atypical flavin reductase encoded by the pden_5119 gene in Paracoccus denitrificans

Pden_5119, annotated as an NADPH-dependent FMN reductase, shows homology to proteins assisting in utilization of alkanesulfonates in other bacteria. Here, we report that inactivation of the pden_5119 gene increased susceptibility to oxidative stress, decreased growth rate and increased growth yield; growth on lower alkanesulfonates as sulfur sources was not specifically influenced. Pden_5119 transcript rose in response to oxidative stressors, respiratory chain inhibitors and terminal oxidase downregulation. Kinetic analysis of a fusion protein suggested a sequential mechanism in which FMN binds first, followed by NADH. The affinity of flavin toward the protein decreased only slightly upon reduction. The observed strong viscosity dependence of k_cat demonstrated that reduced FMN formed tends to remain bound to the enzyme where it can be re-oxidized by oxygen or, less efficiently, by various artificial electron acceptors. Stopped flow data were consistent with the enzyme-FMN complex being a functional oxidase that conducts the reduction of oxygen by NADH. Hydrogen peroxide was identified as the main product. As shown by isotope effects, hydride transfer occurs from the pro-S C4 position of the nicotinamide ring and partially limits the overall turnover rate. Collectively, our results point to a role for the Pden_5119 protein in maintaining the cellular redox state.

Whole Cell Actinobacteria as Biocatalysts

Production of fuels, therapeutic drugs, chemicals, and biomaterials using sustainable biological processes have received renewed attention due to increasing environmental concerns. Despite having high industrial output, most of the current chemical processes are associated with environmentally undesirable by-products which escalate the cost of downstream processing. Compared to chemical processes, whole cell biocatalysts offer several advantages including high selectivity, catalytic efficiency, milder operational conditions and low impact on the environment, making this approach the current choice for synthesis and manufacturing of different industrial products. In this review, we present the application of whole cell actinobacteria for the synthesis of biologically active compounds, biofuel production and conversion of harmful compounds to less toxic by-products. Actinobacteria alone are responsible for the production of nearly half of the documented biologically active metabolites and many enzymes; with the involvement of various species of whole cell actinobacteria such as Rhodococcus, Streptomyces, Nocardia and Corynebacterium for the production of useful industrial commodities.

Biodesulfurization of Petroleum Distillates—Current Status, Opportunities and Future Challenges

Sulfur oxide (SO2) and hydrogen sulfide (H2S) are considered as one of the major air pollutants in the world today. In addition, high sulfur levels in petroleum distillates can promote the deactivation of catalysts through poisoning in fluidized catalytic cracking (FCC) during hydrocracking of the heavy distillates to lighter ones. The presence of high sulfur-containing compounds in the process streams could cause corrosion of piping and fittings and equipment, thereby damaging the pipelines and leading to air emissions of sulfur-containing compounds, which are undesirable for mankind and his environment. In many cases, a large quantity of SOx is released into the atmosphere when petroleum distillates that contain substantial amount of sulphur-containing compounds are used as fuel and combust. In this article, a short overview of different desulfurization methods that are employed to remove sulfur from petroleum distillates is provided. In particular, the review concentrates on biodesulfurization technique. In addition, this article intends to provide its readers current status of biodesulfurization (BDS). It critically analyses the trend in the development of the technology to showcase its strength and weakness that could pave a way for future opportunities. Approaches that are suitable to remediate sulfur-contaminated environment are discussed as well. Lastly, speculations on future directions or opportunities that require exploration are provided as a way of provoking the thoughts of researchers in this field.

Improving the Catalytic Power of the DszD Enzyme for the Biodesulfurization of Crude Oil and Derivatives

The enhancement of the catalytic power of enzymes is a subject of enormous interest both for science and for industry. The latter, in particular, due to the vast applications enzymes can have in industrial processes, for instance in the desulfurization of crude oil, which is mandatory by law in many developed countries and is currently performed using costly chemical processes. In this work we sought to enhance the turnover rate of DszD from Rhodococcus erythropolis, a NADH-FMN oxidoreductase responsible for supplying FMNH₂ to DszA and DszC in the biodesulfurization process of crude oil, the 4S pathway. For this purpose, we replaced the wild type spectator residue of the rate limiting step of the reduction of FMN to FMNH₂ , a process catalysed by DszD and known to play an important role in the reaction energy profile. As replacements, we used all the naturally occurring amino acids, one at a time, using computational methodologies, and repeated the above-mentioned reaction with each mutant. To calculate the different free energy profiles, one for each mutated model, we applied quantum mechanics/molecular mechanics (QM/MM) methods within an ONIOM scheme. The free energy barriers obtained varied between 15.1 and 29.9 kcal mol^-1 . Multiple factors contributed to the different ΔG values. The most relevant were electrostatic interactions and the induction of a favourable alignment between substrate and cofactor. These results confirm the great potential that chirurgic mutations have for increasing the catalytic power of DszD in relation to the wild type (wt) enzyme.

Metabolic and process engineering for biodesulfurization in Gram-negative bacteria

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.

DBT desulfurization by decorating Rhodococcus erythropolis IGTS8 using magnetic Fe3O4 nanoparticles in a bioreactor

Today, crude oil is an important source of energy and environmental contamination due to the continued use of petroleum products is a matter or urgent concern. In this work, two technological platforms, namely, the use of a robust desulfurizing bacteria and the use of nanotechnology to decorate the surface of the bacteria with nanoparticles (NP), were combined to enhance biodesulfurization (BDS). BDS is an ecologically friendly method for desulfurizing petroleum products while avoiding damage to the hydrocarbons due to the high temperatures normally associated with physical desulfurization methods. First, a bacterium known to be a good organism for desulfurization (Rhodococcus erythropolis IGTS8) was employed in cell culture to remove a recalcitrant sulfur molecule from a common sulfur-containing compound found in crude petroleum products (dibenzothiophene). 2-Hydroxybiphenyl (2-HBP) produced as a consequence of the BDS of dibenzothiophene was determined using Gibbs' assay. The synthesized NP were characterized by field emission scanning electron microscope, transmission electron microscopy, Fourier transform infrared spectroscopy, X-ray diffraction spectroscopy, and vibrating sample magnetometer. The field emission scanning electron microscope and transmission electron microscopy images showed the size of the NP is 7-8 nm. The decorated cells had a long lag phase, but the growth continued until 148 h (at OD₆₀₀ = 3.408) while the noncoated bacteria grow until 96 h before entering the stationary phase at OD₆₀₀ = 2.547. Gibbs' assay results showed that production of 2-HBP by decorated cells was 0.210 mM at t = 148 h, while 2-HBP production by nondecorated cells was 0.182 mM at t = 96 h. Finally, the experiments were repeated in a fermenter.

Engineering synthetic bacterial consortia for enhanced desulfurization and revalorization of oil sulfur compounds

The 4S pathway is the most studied bioprocess for the removal of the recalcitrant sulfur of aromatic heterocycles present in fuels. It consists of three sequential functional units, encoded by the dszABCD genes, through which the model compound dibenzothiophene (DBT) is transformed into the sulfur-free 2-hydroxybiphenyl (2HBP) molecule. In this work, a set of synthetic dsz cassettes were implanted in Pseudomonas putida KT2440, a model bacterial "chassis" for metabolic engineering studies. The complete dszB1A1C1-D1 cassette behaved as an attractive alternative - to the previously constructed recombinant dsz cassettes - for the conversion of DBT into 2HBP. Refactoring the 4S pathway by the use of synthetic dsz modules encoding individual 4S pathway reactions revealed unanticipated traits, e.g., the 4S intermediate 2HBP-sulfinate (HBPS) behaves as an inhibitor of the Dsz monooxygenases, and once secreted from the cells it cannot be further taken up. That issue should be addressed for the rational design of more efficient biocatalysts for DBT bioconversions. In this sense, the construction of synthetic bacterial consortia to compartmentalize the 4S pathway into different cell factories for individual optimization was shown to enhance the conversion of DBT into 2HBP, overcome the inhibition of the Dsz enzymes by the 4S intermediates, and enable efficient production of unattainable high added value intermediates, e.g., HBPS, that are difficult to obtain using the current monocultures.

Advances in the Reduction of the Costs Inherent to Fossil Fuels' Biodesulfurization towards Its Potential Industrial Application

Biodesulfurization (BDS) process consists on the use of microorganisms for the removal of sulfur from fossil fuels. Through BDS it is possible to treat most of the organosulfur compounds recalcitrant to the conventional hydrodesulfurization (HDS), the petroleum industry's solution, at mild operating conditions, without the need for molecular hydrogen or metal catalysts. This technique results in lower emissions, smaller residue production and less energy consumption, which makes BDS an eco-friendly process that can complement HDS making it more efficient. BDS has been extensively studied and much is already known about the process. Clearly, BDS presents advantages as a complementary technique to HDS; however its commercial use has been delayed by several limitations both upstream and downstream the process. This study will comprehensively review and discuss key issues, like reduction of the BDS costs, advances and/or challenges for a competitive BDS towards its potential industrial application aiming ultra low sulfur fuels.

Preferential desulfurization of dibenzyl sulfide by an isolated Gordonia sp. IITR100

Several organosulfur compounds are present in the crude oil, and are required to be removed before its processing into transport fuel. For this reason, biodesulfurization of thiophenic compounds has been studied extensively. However, studies on the sulfide compounds are scarce. In this paper, we describe desulfurization of a model sulfidic compound, dibenzyl sulfide (DBS) by an isolated Gordonia sp. IITR100. The reaction was accompanied with the formation of metabolites dibenzyl sulfoxide, dibenzyl sulfone and benzoic acid. Studies with recombinant E. coli revealed that enzyme DszC of this isolate metabolizes DBS into dibenzyl sulfoxide and dibenzyl sulfone, but the reaction downstream to it is mediated by some enzyme other than its DszA. In reactions where DBS and dibenzothiophene (DBT) were present together, both IITR100 and recombinant E. coli exhibited preference for the desulfurization of DBS over DBT. The newly identified capability of IITR100 for desulfurization of both thiophenic and sulfidic compounds suggests its potential use in improved desulfurization of petroleum fractions.

Ultrasound assisted biodesulfurization of liquid fuel using free and immobilized cells of Rhodococcus rhodochrous MTCC 3552: A mechanistic investigation

This paper attempts to gain mechanistic insight into enhancement effect of sonication on biodesulfurization. The approach has been to fit Haldane kinetics model to dibenzothiophene (DBT) metabolism and analyze trends in model parameters concurrently with simulations of cavitation bubble dynamics. Mechanistic synergy between sonication and biodesulfurization is revealed to be of both physical and chemical nature. Generation of micro-turbulence in medium by sonication leads to fine emulsification and enhancement of DBT transport across organic/aqueous interphase. Microturbulence also enhances transport of substrate and product across cell wall that increases reaction velocity (Vmax). Michaelis constant (Km) and inhibition constant (KI), being intrinsic parameters, remain unaffected by sonication. Radicals produced by transient cavitation oxidize DBT to DBT-sulfoxide and DBT-sulfone (intermediates of metabolism), which contributes enhancement of biodesulfurization. However, high shear generated by ultrasound and cavitation has adverse effect on action of surfactant β-cyclodextrin for enhancement of interphase transport of DBT.

A novel metabolite (1,3-benzenediol, 5-hexyl) production by Exophiala spinifera strain FM through dibenzothiophene desulfurization

Sulfur dioxide which is released from petroleum oil combustion causes pollution over the atmosphere and the soil. Biodesulfurization can be used as a complementary method of hydrodesulfurization, the common method of petroleum desulfurization in refineries. Many studies have been carried out to develop biological desulfurization of dibenzothiophene (DBT) with bacterial biocatalysts. However, fungi are capable to metabolize a wide range of aromatic hydrocarbons through cytochrome P450 and their extracellular enzymes. The aim of the present work was isolation and identification of fungi biocatalysts capable for DBT utilization as sulfur source and production of novel metabolites. DBT consumption and the related produced metabolites were analyzed by HPLC and GC-MS respectively. One of the isolated fungi that could utilize DBT as sole sulfur source was identified by both traditional and molecular experiments and registered in NCBI as Exophiala spinifera FM strain (accession no. KC952672). This strain could desulfurize 99 % of DBT (0.3 mM) as sulfur source by co-metabolism reaction with other carbon sources through the same pathway as 4S and produced 2-hydroxy biphenyl (2-HBP) during 7 days of incubation at 30 °C and 180 rpm shaking. However, the isolate was able to transform 2-HBP to 1,3-benzenediol, 5-hexyl. While biphenyl compounds are toxic to leaving cells, biotransformation of them can reduce their toxicity and the fungi will be more tolerant to the final product. These data are the first report about the desulfurization of DBT comparable to 4S-pathway and production of innovative metabolite by E. spinifera FM strain.

Biocatalytic desulfurization of thiophenic compounds and crude oil by newly isolated bacteria

Microorganisms possess enormous highly specific metabolic activities, which enable them to utilize and transform nearly every known chemical class present in crude oil. In this context, one of the most studied biocatalytic processes is the biodesulfurization (BDS) of thiophenic sulfur-containing compounds such as benzothiophene (BT) and dibenzothiophene (DBT) in crude oils and refinery streams. Three newly isolated bacterial strains, which were affiliated as Rhodococcus sp. strain SA11, Stenotrophomonas sp. strain SA21, and Rhodococcus sp. strain SA31, were enriched from oil contaminated soil in the presence of DBT as the sole S source. GC-FID analysis of DBT-grown cultures showed consumption of DBT, transient formation of DBT sulfone (DBTO₂) and accumulation of 2-hydroxybiphenyl (2-HBP). Molecular detection of the plasmid-borne dsz operon, which codes for the DBT desulfurization activity, revealed the presence of dszA, dszB, and dszC genes. These results point to the operation of the known 4S pathway in the BDS of DBT. The maximum consumption rate of DBT was 11 μmol/g dry cell weight (DCW)/h and the maximum formation rate of 2-HBP formation was 4 μmol/g DCW/h. Inhibition of both cell growth and DBT consumption by 2-HBP was observed for all isolates but SA11 isolate was the least affected. The isolated biocatalysts desulfurized other model DBT alkylated homologs. SA11 isolate was capable of desulfurizing BT as well. Resting cells of SA11 exhibited 10% reduction in total sulfur present in heavy crude oil and 18% reduction in total sulfur present in the hexane-soluble fraction of the heavy crude oil. The capabilities of the isolated bacteria to survive and desulfurize a wide range of S compounds present in crude oil are desirable traits for the development of a robust BDS biocatalyst to upgrade crude oils and refinery streams.