Endogenous physical regulation of population density in the freshwater protozoan Paramecium caudatum

Abstract

Studies confirm physical long-range cell-cell communication, most evidently based on electromagnetic fields. Effects concern induction or inhibition of cell growth. Their natural function is unclear. With the protozoan Paramecium caudatum I tested whether the signals regulate cell density and are electromagnetic. Up to 300 cells/mL, cell growth in clones of this study is decreasingly pronounced. Using cuvettes as chemical barriers enabling physical communication I placed 5 indicator cells/mL, the inducer populations, into smaller cuvettes that stand in bigger and contained 50, 100, 200 or 300 cells/mL. Under conditions of total darkness such pairs were mutually exposed for 48 hours. The hypothesis was that indicator cells, too, grow less the more neighbor cells there are. The bigger inducer populations were in the beginning the less they grew. The indicator populations grew accordingly; the more cells they were surrounded by the less they grew. The suppressing neighbors-effect disappeared when inner cuvettes were shielded by graphite known to shield electromagnetic radiation from GHz to PHz, i.e. to absorb energy from microwaves to light. These are the first results demonstrating non-contact physical quorum sensing for cell population density regulation. I assume rules intrinsic to electromagnetic fields interacting with matter and life.

Figure 1

Panel (a) and (d) refer to Material & Method, panel (b), (c) and (e) to Results. (a) Visualization of the experimental setup. (b) Growth of inducer populations. The x-axis shows the densities of the inducer populations at the beginning of the experiment. The y-axis show log transformed growth rates of these inducer populations. The bigger the inducer populations were at the beginning the less they were growing. (c) Growth of tester (indicator) populations. The x-axis shows the densities of the inducer populations at the beginning of the experiment. The y-axis show log transformed growth rates of tester populations. The bigger the inducer populations were at the beginning the less the tester populations were growing. (d) Arrangement of units in a grid. All units – small cuvette standing in a big one, i.e. treatment group(s) – have been optically shielded from each other (by black cardboard of 0.33 mm thickness). In a typical experiment, the units are placed in a random design. Note, that volatiles – if existing – would affect the outcome by influencing all units across a microclimate. (e) Effect of graphite shielding. Shielded cells grow better than non-shielded tester populations when (both are) having neighbors.