Improvement in desulfurization of dibenzothiophene and dibenzothiophene sulfone by Paenibacillus strains using immobilization or nanoparticle coating

AIMS

Biodesulfurization of fossil fuels is a promising technology for deep desulfurization. Previously we have shown that Paenibacillus strains 32O-W and 32O-Y can desulfurize dibenzothiophene (DBT) and DBT sulfone (DBTS) effectively. In this work, improvements in DBT and DBTS desulfurization by these strains were investigated through immobilization and nanoparticle coating of cells.

METHODS AND RESULTS

Paenibacillus strains 32O-W and 32O-Y immobilized in alginate gel beads or coated with Fe₃ O₄ magnetite nanoparticles were grown at various concentrations (0.1-2 mmol l^-1 ) of DBT or DBTS for 96 h. The production of 2-hydroxybiphenyl (2-HBP) from 4S pathway biotransformation of DBT or DBTS was measured. The highest amounts of 2-HBP production occurred at concentrations of 0.1 and 0.5 mmol l^-1 . Compared to planktonic cultures maximum 2-HBP production increased by 54 % for DBT and 90 % for DBTS desulfurization with immobilized strains, and 44 % for DBT and 66% for DBTS desulfurization by nanoparticle coated strains.

CONCLUSIONS

Nanoparticle coated and immobilized cells may be of use in efforts to increase the efficiency of biodesulfurization.

SIGNIFICANCE AND IMPACT OF STUDY

Alginate immobilization or nanoparticle coating of bacterial cells may be useful approaches for enhancement of biodesulfurization for eventual use at an industrial scale.

Development of molecular driven screening for desulfurizing microorganisms targeting the dszB desulfinase gene

COnsensus DEgenerate Hybrid Oligonucleotide Primers (CODEHOP) were developed for the detection of the dszB desulfinase gene (2'-hydroxybiphenyl-2-sulfinate desulfinase; EC 3.13.1.3) by polymerase chain reaction (PCR), which allow to reveal larger diversity than traditional primers. The new developed primers were used as molecular monitoring tool to drive a procedure for the isolation of desulfurizing microorganisms. The primers revealed a large dszB gene diversity in environmental samples, particularly in diesel-contaminated soil that served as inoculum for enrichment cultures. The isolation procedure using the dibenzothiophene sulfone (DBTO₂) as sole sulfur source reduced drastically the dszB gene diversity. A dszB gene closely related to that carried by Gordonia species was selected. The desulfurization activity was confirmed by the production of desulfurized 2-hydroxybiphenyl (2-HBP). Metagenomic 16S rRNA gene sequencing showed that the Gordonia genus was represented at low abundance in the initial bacterial community. Such observation highlighted that the culture medium and conditions represent the bottleneck for isolating novel desulfurizing microorganisms. The new developed primers constitute useful tool for the development of appropriate cultural-dependent procedures, including medium and culture conditions, to access novel desulfurizing microorganisms useful for the petroleum industry.

Combining co-culturing of Paenibacillus strains and Vitreoscilla hemoglobin expression as a strategy to improve biodesulfurization

Enhancement of the desulfurization activities of Paenibacillus strains 32O-W and 32O-Y were investigated using dibenzothiophene (DBT) and DBT sulfone (DBTS) as sources of sulphur in growth experiments. Strains 32O-W, 32O-Y and their co-culture (32O-W plus 32O-Y), and Vitreoscilla hemoglobin (VHb) expressing recombinant strain 32O-Yvgb and its co-culture with strain 32O-W were grown at varying concentrations (0·1-2 mmol l^-1 ) of DBT or DBTS for 96 h, and desulfurization measured by production of 2-hydroxybiphenyl (2-HBP) and disappearance of DBT or DBTS. Of the four cultures grown with DBT as sulphur source, the best growth occurred for the 32O-Yvgb plus 32O-W co-culture at 0·1 and 0·5 mmol l^-1 DBT. Although the presence of vgb provided no consistent advantage regarding growth on DBTS, strain 32O-W, as predicted by previous work, was shown to contain a partial 4S desulfurization pathway allowing it to metabolize this 4S pathway intermediate.