Discover how Myxococcus xanthus performs a complete "factory reset" on its internal navigation system after every cell division.
Imagine a city where every time a new building was completed, all the doors, roads, and traffic signals reset to a blank slate. Chaos would ensue, but only temporarily, before a new, organized layout emerged. In the microscopic world, something remarkably similar happens.
For cells, "front" and "back" aren't arbitrary—this polarity is crucial for movement, feeding, and communication. For the social bacterium Myxococcus xanthus, a master of coordination, this process is vital. Recent research reveals a fascinating secret: every time it divides, it performs a complete "factory reset" on its internal navigation system. This isn't a bug; it's a brilliant feature that ensures its survival.
Cell polarity defines directionality in cellular processes, much like a compass guides navigation.
Division erases all existing polarity, allowing each new cell to establish its own direction independently.
Before we dive into the reset, let's meet our protagonist. Myxococcus xanthus is a soil-dwelling bacterium, often called a "social bacterium" or "wolf pack" hunter because it swarms collectively to prey on other microbes.
Unlike many bacteria that swim with whip-like flagella, M. xanthus glides smoothly over surfaces using two ingenious molecular engines:
This engine is like a tank tread. Imagine molecular treads inside the cell's membrane that circulate, gripping the surface and propelling the bacterium forward. This system allows individual cells to strike out on their own.
This is more like a grappling hook. The bacterium extends a sticky, spear-like pilus from its front, attaches to a surface or another cell, and then retracts it to pull itself along. This is essential for moving in coordinated groups.
Both of these systems require the cell to have a defined front (leading edge) and back (lagging edge). This polarity is established by a protein called MglA, a molecular switch that, when active (bound to GTP), localizes to the front of the cell and tells the motility machinery where to assemble.
When a rod-shaped bacterium like M. xanthus prepares to divide, it elongates and then pinches in the middle to create two daughter cells. This raised a critical question for scientists: At the moment of division, each daughter cell inherits one "old" pole (from the mother cell) and one "new" pole (the division site). Does the existing polarity from the mother cell get passed down, or is it erased and re-established from scratch?
A crucial experiment by scientists at the University of Basel provided a clear answer. They set out to watch polarity in real-time throughout the entire cell division process.
The researchers used a powerful combination of tools to make the invisible visible.
They genetically engineered M. xanthus cells so that the key polarity protein, MglA, was fused to a green fluorescent protein (GFP). When placed under a high-resolution fluorescence microscope, the MglA protein would glow green, revealing its precise location inside the cell.
They placed the glowing bacteria on a nutrient-poor surface and filmed them for several hours under the microscope, capturing an image every few minutes.
They carefully tracked individual cells as they moved, grew, and eventually divided. By analyzing the videos, they could see exactly where the bright green spot of MglA was located before, during, and after division.
| Tool / Reagent | Function in the Experiment |
|---|---|
| Fluorescent Protein (GFP) | A molecular "tag" that is fused to a protein of interest (like MglA), allowing scientists to visualize its location and movement inside a living cell under a microscope. |
| Time-Lapse Fluorescence Microscopy | A technique for taking repeated images of living cells over time. It was essential for capturing the dynamic process of polarity loss and regain during division. |
| MglA Mutants | Genetically altered versions of the MglA protein that are "stuck" in an always-on or always-off state. These were used to confirm MglA's role as the master polarity switch. |
| Minimal Agar Plates | A simple, nutrient-poor gel surface on which the bacteria are grown for microscopy. It encourages motility and ensures the cells remain flat and in focus for imaging. |
The results were striking and consistent. The data told a clear story of erasure and rebirth.
This was the smoking gun. If polarity were simply inherited, one daughter would always keep the old front, and the other would be born with a random front. The complete erasure and random re-establishment proved that cell division acts as a hard reset for cellular polarity.
| Cell Stage | MglA Localization | Cell Motility |
|---|---|---|
| Mother Cell | Single focus at one pole | Motile |
| Dividing Cell | Signal lost; no focus | Non-motile |
| Daughter Cells | New focus at random pole | Motile |
| Experimental Condition | Effect on Polarity Reset | Outcome for Population |
|---|---|---|
| Normal Wild-Type Cells | Clean reset after division | Healthy mix of movement directions; efficient swarming |
| Mutant Cells (defective reset) | Polarity inherited or stuck | Daughters move in same direction; chaotic, inefficient movement; failed swarm expansion |
This reset is more than just a curious cellular quirk; it's a profound survival strategy. By randomizing direction after every division, the bacterial population ensures maximum exploration of its environment. If both daughters always followed the mother's path, the swarm would be a narrow, single-file line, easily missing nearby prey.
Instead, the reset creates a constantly expanding, dynamic front, perfect for hunting as a pack.
The discovery that a fundamental process like cell division includes a step to erase cellular memory teaches us a broader lesson in biology: Order often emerges from a deliberate step back into chaos. For Myxococcus xanthus, this cyclical dance of structure and reset is the key to its successful, social life.
The deliberate erasure of polarity during division ensures population diversity in movement direction, enhancing environmental exploration and collective survival.