Effect of dibenzothiophene and its alkylated derivatives on coupled desulfurization and carotenoid production by Gordonia alkanivorans strain 1B.

Nowadays, the production of green transportation fuels is essential for a healthy life and environment. Effective and complete removal of organosulfur recalcitrant compounds from fuel oils is crucial to meet the stringent requirements of sulfur standards. However, the industry's solution (Hydrodesulfurization, HDS) is not effective in the removal of complex sulfur heterocyclic hydrocarbons. Thus, the development of more efficient and ecofriendly/sustainable desulfurization methods is critical, as either an alternative or a complement to HDS, foreseeing the production of ultra-low sulfur fuels (ULSF). Among the desulfurization techniques available, microbial desulfurization of organosulfur hydrocarbons (biodesulfurization, BDS) is attracting great attention. BDS is carried out at mild operation conditions, making it energetically cheaper and more ecofriendly, since it does not require hydrogen and produces far less greenhouse gases emission than HDS. In this context, the behavior of Gordonia alkanivorans strain 1B, a desulfurizing bacterium and hyper-pigment producer, was evaluated in the presence of four sulfur sources common in fuel oils: dibenzothiophene (DBT); 4-mDBT; 4,6-dmDBT and 4,6-deDBT (single/mixed), in terms of both desulfurization rate and overall carotenoid production. Simultaneously, the influence of the carbon source used (fructose vs glucose) on the overall effectiveness of the coupled bioprocesses was also assessed. The results obtained highlight the potential of strain 1B to desulfurize all the tested recalcitrant compounds and simultaneously produce carotenoids. However, the highest BDS values were observed for 4,6-deDBT (5.75 μmol/g (DCW)/h) and for the mix of DBTs (5.20 μmol/g (DCW)/h), when fructose was used as carbon source. Indeed, when the mixture of DBTs ("model oil surrogate") was desulfurized by cells growing in fructose both desulfurization rate and total pigments amount were higher than those observed for glucose growing cells. Moreover, under these conditions, the strain 1B was able to produce high added-value carotenoids, namely astaxanthin, lutein and canthaxanthin. Hence, these results are promising when aiming to achieve a scale-up scenario. In fact, the inclusion of the production of high added-value products within a BDS process targeting ULSF may be a sustainable way to turn its scale-up economically viable.
Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
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