Understanding cell division and its regulation in the human pathogenic bacterium, Vibrio parahaemolyticus

Bacteria undergo a well-orchestrated cell division process with a highly regulated placement of the division site in order to generate progeny cells with complete hereditary information. Thus, bacteria have evolved mechanisms to govern the spatio-temporal dynamics and localization of cell division proteins in accordance with the cell cycle. Cell division needs to be particularly tightly regulated in differentiating bacteria where changes between different cell morphologies increases the complexity of the process. Vibrio parahaemolyticus exists as swimmer and swarmer cells, specialized for growth in liquid and on solid environments, respectively. Swarmer cells are highly elongated by a probable regulated inhibition of cell division. But, these cells still need to divide in order to proliferate and expand the colony. The regulators that facilitate the drastically different cell sizes between the two cell types and the factors that control their cell divisions are unknown. Here we show that swarmer cells of all lengths undergo cell divisions, but the placement of the division site is cell length-dependent. The short swarmer cells divide at mid-cell whereas the long swarmer cells divide at a non-mid-cell (pole-proximal) division site. We show that the transition to non-mid-cell positioning of the division site is cell length-dependent. Our research reveals that V. parahaemolyticus uses the Min system to mark the length-dependent (LD) division site in the swarmer cells. Through microscopy experiments we demonstrate that the dynamics of the division regulator MinD switches from a pole-to-pole oscillation in short swarmer cells to a multi-node standing-wave oscillation in long swarmer cells. Additionally, the regulation of FtsZ levels restricts the number of divisions to one per cell cycle and the nucleoid occlusion determinant SlmA ensures sufficient free FtsZ to sustain Z-ring formation by preventing sequestration of FtsZ into division deficient clusters over the nucleoid. We also show that, in spite of several Min minima that arise during a standing wave oscillation of MinD, the cell divides at the utmost pole-proximal Min minimum. By limiting the number of division events to one per cell, V. parahaemolyticus promotes the preservation of long swarmer cells and permits swarmer cell division without the need for dedifferentiation. Additionally, we show that the ParA-like ATPase, ParC, that has previously been described to be the cell pole-determinant in Vibrios, also regulates the localization of the major cell division protein FtsZ in swarmer cells, and thereby prevents polar division events. Altogether, this work sheds light to the study of cell division in the di-morphic pathogenic bacterium, V. parahaemolyticus. For the first time, we demonstrate a cell length-dependent division site placement in naturally occurring bacteria by employing Min oscillation. The identification of ParC as a protein of dual-function ties together the spatio-temporal regulation of diverse processes such as bacterial chemotaxis, cell pole development and regulation of cell division