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Slime molds

Network formation

Satellites

Generally, Physarum grows into a tubular network in order to forage. However, under starvation conditions, Physarumproduces small fragments, satellites, that move away radially from the point of inoculation. Since this alternative growth progression, termed a search pattern, was observed under starvation conditions, satellites are likely an emergency mechanism of Physarum for survival. To this end, a scaling analysis has been performed to describe the search pattern based on the assumption that Physarum will maximize the area surveyed by satellites.

Oscillations

The oscillations of micro- and macroplasmodia alike are based on the interaction of actin and myosin. We monitor microplasmodia dynamics by observing area oscillations with bright-field microscopy whereby the spatio-temporal dynamics of focal area and contour can be analyzed. Fast oscillations with a period of 1-2 min as well as several superimposed slow oscillations can be found.

Networks

Network theory is vital for the understanding of many real-world systems, such as the vascular system, which is difficult to study in vivo. P. polycephalum is a suitable model organism because it is easy to manipulate. Thus, we strive to understand the dynamics of the vast networks, which originate from accreting microplasmodia. When small amoebae are placed in clusters upon an agar surface, they will crawl around and eventually fuse to form a larger network, which then grows from a few microns to several centimetres, again forming a veinous macroplasmodium. We study the topological phase transition from single microplasmodia into an elaborate network applying graph theory. Function of the network is found to be closely tied to the emergence of structure.

Force measurements

For a detailed understanding of the fundamental processes of cell motility, it is necessary to investigate mechanical properties of the cell. Deformation occurs in response to physical forces, which can either come from the external environment or are intracellularly generated. By testing the reaction to an applied stress and recording the response, it is possible to gather insights into the mechanical properties of the actomyosin cytoskeleton of P. polycephalum. However, existing models mostly treat cells as a homogenous mass of cytoplasm, surrounded by a membrane. We investigated the ultrastructure of microplasmodia using transmission electron microscopy (TEM) and scanning electron microscopy and found a porous, sponge-like internal structure with elaborate channels, connected to the surface via pores. This channel system reacts different to deformation than a homogenous mass of cytoplasm and has to be taken into account when assessing the force measurements.