Physical Basis for Coordination among Bacterial Cells in a Proto-Multicellular Colony

Multi-cellular Magnetotactic Bacteria are the only known obligately multi-cellular bacteria. Cells live within a colony composed of 10-50 cells. Each cell precipitates a magnetic crystal. The average magnetic moment of the colony aligns with the Earth’s magnetic field. The outer surface of each cell is covered in about 30 flagella. Colonies move as a single unit as individual cells in the colony rotate their flagella. It is not understood how cells in a colony align their magnetosomes, how this order is maintained during division, or how cells coordinate their flagella to exert a force parallel to their average magnetic moment. Here, we propose a physical mechanism to show this coordination may arise without direct cell-cell communication. We use published data to show that the organization of the cells in a colony is consistent with a Fibonacci packing. Next, we show that coupling chemotaxis to magnetotaxis allows cells to exert a net force parallel to the average magnetic moment of the colony. These results give insight into the evolution of complex life by showing that cells in a protomulticellular organism may coordinate their behaviors through purely physical mechanisms before the evolution of shared chemical signaling pathways.