While pH is known to have pronounced effects on the phase behaviour of MO/OA/H2O systems, it did not account for the phase changes observed (Table ). The V₂→H₂ transformation induced by S. aureus is consistent with two separate mechanisms: the action of lipase , or the transfer of phospholipids from bacterial cell membranes into the lipid cubic phase. The enzymatic hydrolysis of monoolein, and subsequent accumulation of oleic acid in the lipid matrix, is known to cause a transformation to more negatively-curved bilayer structures. The H₂→I₂ transformation observed for monoolein hexosomes is also consistent with the lipid matrix becoming enriched with oleic acid. Alternatively, these phase transitions can be attributed to the transfer of phospholipids from bacterial cell membranes to the lipid matrix. Bacterial cell membranes are abundant in phosphatidylethanolamine (PE) which promotes negative bilayer curvature and the transformation to H₂ structure in monoolein systems at >34 wt.%. However, other bacterial phospholipids such as cardiolipin (CL) promote positive bilayer curvature and the transformation to Lα structure at <1 wt.%. The effect of phospholipids on MO/OA/H2O systems is not described in the literature. Thus, understanding the phase behaviour of monoolein systems upon incorporation of the suite of bacterial phospholipids present their cellular membranes is necessary to delineate the mechanism driving these structural transformations.