FUSED NUCLEOIDS RESEGREGATE FASTER THAN CELL ELONGATION IN ESCHERICHIA-COLI PBPB(TS) FILAMENTS AFTER RELEASE FROM CHLORAMPHENICOL INHIBITION

The course of nucleoid movement during and upon release from protein s ynthesis inhibition by chloramphenicol in filaments of Escherichia coi l pbpB(Ts) was analysed. Cells were grown at 42 degrees C in glucose m inimal medium for two mass doublings and were treated with chloramphen icol to generate fusion (coalescence) of the nucleoids. Upon release f rom protein synthesis inhibition, the large distance between the borde r of the fused nucleoids and the cell poles immediately decreased, bef ore full recovery of the rates of mass growth and length increase at 3 0 degrees C. This indicates that nucleoids can reoccupy the DNA-free c ell ends independently of cell elongation. During filamentation at 42 degrees C, the pbpB cells established initial constrictions at midcell and at one-quarter and three-quarter positions. Nevertheless, divisio ns only started 75 min after chloramphenicol removal at 30 degrees C, when most nucleoids had moved back into the vacated cell ends. No 'gui llotine-like' constrictions at the site of the nucleoids occurred. Thi s suggests that segregating nucleoids postpone division recovery at pr eviously established sites. The results are discussed in the light of a working model for transcription/translation-mediated chromosome segr egation and nucleoid occlusion of cell division.