Labelling of eicosapentaenoic acid with stable isotope 13C in the marine bacterium Shewanella marinintestina

Abstract

Eicosapentaenoic acid (EPA) is an essential omega-3 polyunsaturated fatty acid that plays a critical role in marine life. It is present in several marine animals, including fish, but the primary producers of EPA are phytoplankton and specific marine bacteria. Although most of the EPA present in marine animals come from phytoplankton, the bacterial input into the marine EPA food web is still unknown. The labelling of EPA within a bacterial strain could be a viable strategy to help revealing this contribution. In this work, Shewanella marinintestina IRL 567, a marine bacterium isolated from fish guts and known to produce EPA, was labelled with the stable isotope ¹³C at small (250-mL shake flask), bench (2.5-L shake flask), and pilot scale (50-L stirred tank bioreactor). Growing the bacterium with ¹³C-acetate in the culture medium demonstrated that EPA was de-novo synthesized utilizing acetate as precursor. ¹³C incorporation into the EPA molecule resulted in values as high as 95.5% of the synthesized EPA being labelled in small scale, 95.9% in bench scale and 91.5% in pilot scale. This simple method to label EPA proved to be effective and therefore it could be a valuable tool to follow the fate of bacterial EPA into higher trophic levels.

Keywords: Eicosapentaenoic acid; Fatty acid; Labelling; Marine bacteria; Shewanella marinintestina; Stable isotope probing.