Identification and characterization of outer membrane fragments released by Aeromonas sp.

Aeromonas hydrophila and Aeromonas salmonicida were shown to release "blebs" or fragments averaging 20-30 nm in diameter. The protein composition of the fragments was very similar to that of the corresponding outer membrane by sodium dodecyl sulphate--polyacrylamide gel electrophoresis and the fragments were shown to contain phospholipid and lipopolysaccharide. The results therefore indicate that the blebs are derived from the outer membrane of these organisms. Fragments isolated directly by differential ultracentrifugation were indistinguishable from fragments isolated by salt fractionation and gel filtration in chemical composition, protein composition, and density. However fragments isolated directly contained much less glycerophospholipid-cholesterol acyltransferase than those isolated by salt fractionation. The potential usefulness of membrane fragments to the bacteria and as a tool in the study of outer membrane structure and function is discussed.