ACID PH RESPONSES OF ESCHERICHIA-COLI - INHIBITION OF COLICIN-V SYNTHESIS AND ACTIVITY AT PH 5.0

On solid medium, streaks of ColV(+) Escherichia coli strains produced much larger inhibitory zones on sensitive indicators at pH 7.0 and 9.0 than at pH 5.0. Such an acid pH effect also occurred in liquid medium , with sensitive strains being killed by ColV(+) ones at pH 7.0 or 9.0 but not at pH 5.0. Colicin V was responsible for the killing effect. Culture filtrates from PAP1401 (ColV(+)) were used to examine the basi s for the pH effect and it was found that acid pH interfered directly or indirectly with colicin V production but that colicin V was not irr eversibly inactivated at pH 5.0. Additionally, colicin V formed at pH 7.0 was less active when tested on sensitive strains at pH 5.0 than at pH 7.0. Neither reduced colicin synthesis nor its reduced activity ca n be attributed to increased availability of iron at pH 5.0.