Functionalization of the model asphaltene 1-dodecylnaphthalene by Pseudomonas aeruginosa KK6 through subterminal metabolism

Abstract

Asphaltenic compounds in heavy oils may be biologically functionalized in the contexts of oil upgrading and in mitigating contamination however there are knowledge gaps in regard to the mechanisms of asphaltene functionalization by microorganisms. Due to the challenges of studying asphaltene functionalization, model asphaltene compounds comprised of polyaromatic centers and long alkyl chains may be utilized. In this work, a soil bacterium identified as Pseudomonas aeruginosa KK6 was characterized and it was found to extensively biotransform the water insoluble polycyclic n-alkylaromatic model asphaltene, 1-dodecylnaphthalene (1-DDN). Gas chromatography was utilized to quantify 1-DDN transformation and liquid chromatography with UV detection coupled to electrospray ionization tandem mass spectrometry (LC-UV/ESI-MS/MS) was used to analyze transformation products. An unusual transformation product profile occurred that showed that varying alkyl chain length compounds that differed by one methylene unit each were detected attached to their polycyclic aromatic chromophores. CID product ion scan analyses revealed that 1-DDN was transformed into oxidized, alkyl chain-shortened, reduced molecular weight 1-naphthyl-alkanoic acids and 1-naphthyl-alkanals and results interpretation supported that these compounds were produced through subterminal oxidation mechanisms by strain KK6. Based upon the results, biotransformation pathways that described the biological functionalization of a model asphaltene compound were constructed. On its own or in conjunction with polycyclic aromatic hydrocarbon-degrading bacteria, this strain may be applied to upgrading heavy oil.