Characterization of extracellular membrane vesicles of an Antarctic bacterium, Shewanella livingstonensis Ac10, and their enhanced production by alteration of phospholipid composition.

A cold-adapted bacterium, Shewanella livingstonensis Ac10, which produces eicosapentaenoic acid (EPA) as a component of its membrane phospholipids, is useful as a model to study the function of EPA and as a host for heterologous production of thermolabile proteins at low temperatures. In this study, we characterized extracellular membrane vesicles (EMVs) of this bacterium to examine the involvement of EPA in the biogenesis of EMVs and for the future application of EMVs to extracellular protein production. We found that this strain produced EMVs from the cell surface. Cryo-electron microscopic observation showed that the majority of the EMVs had a single-bilayer structure with an average diameter of 110 nm, though EMVs with double-bilayer membranes and other diverse structures were also observed. Quantitative analysis demonstrated that the EMV production was significantly increased (3-5 fold) by the depletion of EPA-containing phospholipids. The lack of EPA also altered the protein composition of EMVs. In particular, incorporation of one of the cold-inducible outer membrane proteins, OmpC176, was significantly increased in EMVs after the depletion of EPA. These results provide a basis for the construction of an EMV-based, low-temperature protein production system and show the involvement of EPA in the regulation of EMV biogenesis.