Freeze-Thawing of Aquaspirillum magnetotacticum Cells Selectively Releases Periplasmic Proteins.

Cells of the gram-negative bacterium Aquaspirillum magnetotacticum, when suspended in buffer and freeze-thawed, produced pinkish orange supernatant fluid. The fluid contained </=2.0% of total extractable outer membrane component 2-keto-3-deoxyoctonate or of the cytoplasmic membrane marker succinic dehydrogenase. Electrophoretic banding patterns and difference spectra of proteins and hemoproteins released by freeze-thawing cells were distinct from those of membrane-associated substances and similar to those of periplasmic substances obtained by applying conventional fractionation methods to this organism.