Dibenzothiophene biodesulfurization in resting cell conditions by aerobic bacteria

Rhodococcus erythropolis IGTS8 and the genetically modified strain Pseudomonas putida CECT 5279 are effectively capable to carry out the oxidative non-destructive desulfurization of dibenzothiophene (DBT), called 4S pathway, so that sulfur is released after four enzymatic steps, without carbon skeleton breakdown. Biodesulfurization (BDS) process yields were studied both in aqueous and biphasic media, with hexadecane as model oil. All batch assays were carried out at Erlenmeyer flasks scale, under different experimental conditions such as oil fraction phase percentages, substrate concentrations and cellular densities, using resting cell as operation mode. Providing that cell densities were not too high, both biocatalysts achieved better DBT conversion with higher biomass concentrations and lower oil fractions and DBT concentrations. Comparing aqueous and biphasic media it has been also proved that P. putida CECT 5279 strain was more sensitive for DBT mass transfer limitation, determining the preferable use in biphasic systems of IGTS8 to practical BDS process as well. Furthermore, the experimental results suggested there could be inhibitions effects by product accumulation in aqueous media, but these effects were not so clear in biphasic condition, because 2-hydroxybiphenyl (HBP) oil–water partition coefficient is very high.