INHIBITION BY BACTERIA OF PSEUDOPLASMODIUM FORMATION OF DICTYOSTELIUM DISCOIDEUM

A mutant of Dictyostelium discoideum was isolated, the development of which was normal at 18.5°C but stopped at the aggregate stage when cultured with bacterial associate at 26°C. Probably the bacteria release a factor inhibitory to pseudoplasmodium formation, the inactivation of the inhibitor being temperature-sensitive in this mutant. This bacterial factor is different from the one reported by W eber and R aper (16), judging from the synergism shown by these two types of mutants.
The temperature-shift experiment gave the result that the inhibited developmental step was at about the time of initiation of tip formation. However, once a tip was formed under the permissive conditions, the re-formation of a new tip after removal of the original was not inhibited under the nonpermissive conditions. These results indicate that the bacterial inhibitor acts just before tip formation.