STUDIES ON THE ENERGETICS OF PROAEROLYSIN SECRETION ACROSS THE OUTER-MEMBRANE OF AEROMONAS SPECIES - EVIDENCE FOR A REQUIREMENT FOR BOTH THE PROTONMOTIVE FORCE AND ATP

Aeromonas spp. secrete the channel-forming protein proaerolysin across their inner and outer membranes in separate steps using the general s ecretion pathway. Here we show that treating A. hydrophila or A. salmo nicida with the protonophore carbonyl cyanide m-chorophhenyl hydrazone blocks the second step in transport, secretion across the outer membr ane from the periplasm, under conditions where the ATP levels in the c ell are no different than the levels in control, secreting cells. A th reshold for Delta Psi was observed in the region of 120 mV, below whic h secretion by both species was in hibited. Treatment of cells with ar senate, which lowered ATP levels but did not affect Delta Psi, also re duced secretion from the periplasm, an indication that there is an ATP requirement for this step independent of the requirement for Delta Ps i. Secretion across the outer membrane was also arrested by increasing the osmotic pressure of the medium, even though cellular ATP levels a nd Delta Psi were not affected. This may be due to disruption of some necessary association between the inner and outer membranes.