Fused nucleoids resegregate faster than cell elongation in Escherichia coli pbpB(Ts) filaments after release from chloramphenicol inhibition

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Abstract
The course of nucleoid movement during and upon release from protein synthesis inhibition by chloramphenicol in filaments of Escherichia coli pbpB(Ts) was analysed. Cells were grown at 42 °C in glucose minimal medium for two mass doublings and were treated with chloramphenicol to generate fusion (coalescence) of the nucleoids. Upon release from protein synthesis inhibition, the large distance between the border of the fused nucleoids and the cell poles immediately decreased, before full recovery of the rates of mass growth and length increase at 30 °C. This indicates that nucleoids can reoccupy the DNA-free cell ends independently of cell elongation. During filamentation at 42 °C, the pbpB cells established initial constrictions at midcell and at one-quarter and three-quarter positions. Nevertheless, divisions only started 75 min after chloramphenicol removal at 30 °C, when most nucleoids had moved back into the vacated cell ends. No ‘guillotine-like’ constrictions at the site of the nucleoids occurred.This suggests that segregating nucleoids postpone division recovery at previously established sites. The results are discussed in the light of a working model for transcription/translation-mediated chromosome segregation and nucleoid occlusion of cell division.