Correspondence

Corynebacterium glutamicum is a Gram-positive bacterium that lacks the cell division FtsA protein and actin-like MreB proteins responsible for determining cylindrical cell shape. When the cell division ftsZ gene from C. glutamicum (ftsZCg) was cloned in different multicopy plasmids, the resulting constructions could not be introduced into C. glutamicum; it was assumed that elevated levels of FtsZCg result in lethality. The presence of a truncated ftsZCg and a complete ftsZCg under the control of Plac led to a fourfold reduction in the intracellular levels of FtsZ, generating aberrant cells displaying buds, branches and knots, but no filaments. A 20-fold reduction of the FtsZ level by transformation with a plasmid carrying the Escherichia coli lacI gene dramatically reduced the growth rate of C. glutamicum, and the cells were larger and club-shaped. Immunofluorescence microscopy of FtsZCg or visualization of FtsZCg–GFP in C. glutamicum revealed that most cells showed one fluorescent band, most likely a ring, at the mid-cell, and some cells showed two fluorescent bands (septa of future daughter cells). When FtsZCg–GFP was expressed from Plac, FtsZ rings at mid-cell, or spirals, were also clearly visible in the aberrant cells; however, this morphology was not entirely due to GFP but also to the reduced levels of FtsZ expressed from Plac. Localization of FtsZ at the septum is not negatively regulated by the nucleoid, and therefore the well-known occlusion mechanism seems not to operate in C. glutamicum