DEPENDENCY OF ESCHERICHIA-COLI CELL-DIVISION SIZE, AND INDEPENDENCY OF NUCLEOID SEGREGATION ON THE MODE AND LEVEL OF FTSZ EXPRESSION

Expression of ftsZ in strain VIP205 is dissociated from its natural pr omoters, and is under the control of an inducible tao promoter. This a bolishes the oscillation in ftsZ transcription observed in the wild ty pe, allowing different levels of ftsZ expression. We demonstrate that this construction does not affect the expression of other genes, and h as no effects on replication or nucleoid segregation. A shift in IPTG from 30 mu M, that supports division at wild-type sizes, to lower (6 m u M) or higher (100 mu M) concentrations, indicates that VIP205 cells can divide within a broad range of FtsZ concentrations. Analysis of th e morphological parameters during the transition from one IPTG concent ration to another suggests that the correct timing of ftsZ expression, and the correct FtsZ concentration, are required for division to occu r at normal cell sizes. After a transient division delay during the tr ansition to lower IPTG concentrations, cells in which ftsZ is expresse d continuously (yielding 80% of the wild-type FtsZ levels) divide with the same division time as the wild type, but at the expense of becomi ng 1.5 times larger. A precise control of ftsZ expression is required for normal division, but the existence of additional regulators to mai ntain the correct timing during the cell cycle cannot be ruled out.