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Abstract

Cell division needs to be tightly regulated and closely coordinated with
other cellular processes to ensure the generation of fully viable
offspring. Here, we investigate division site placement by the cell
division regulator MipZ in the alphaproteobacterium Magnetospirillum
gryphiswaldense, a species that forms linear chains of magnetosomes to
navigate within the geomagnetic field. We show that M. gryphiswaldense
contains two MipZ homologs, termed MipZ1 and MipZ2. MipZ2 localizes to
the division site, but its absence does not cause any obvious phenotype.
MipZ1, by contrast, forms a dynamic bipolar gradient, and its deletion
or overproduction cause cell filamentation, suggesting an important role
in cell division. The monomeric form of MipZ1 interacts with the
chromosome partitioning protein ParB, whereas its ATP-dependent dimeric
form shows non-specific DNA-binding activity. Notably, both the dimeric
and, to a lesser extent, the monomeric form inhibit FtsZ polymerization
in vitro. MipZ1 thus represents a canonical gradient-forming MipZ
homolog that critically contributes to the spatiotemporal control of
FtsZ ring formation. Collectively, our findings add to the view that the
regulatory role of MipZ proteins in cell division is conserved among
many alphaproteobacteria. However, their number and biochemical
properties may have adapted to the specific needs of the host organism.