Stress signalling in acellular slime moulds and its detection by conspecifics

Abstract

Unicellular organisms live in unpredictable environments. Therefore, they need to continuously assess environmental conditions and respond appropriately to survive and thrive. When subjected to rapid changes in their environment or to cellular damages, unicellular organisms such as bacteria exhibit strong physiological reactions called stress responses that can be sensed by conspecifics. The ability to detect and use stress-related cues released by conspecifics to acquire information about the environment constitutes an adaptive survival response by prompting the organism to avoid potential dangers. Here, we investigate stress signalling and its detection by conspecifics in a unicellular organism, Physarum polycephalum . Slime moulds were subjected to either biotic (i.e. nutritional) or abiotic (i.e. chemical and light) stressors or left undisturbed while they were exploring a homogeneous environment. Then, we observed the responses of slime moulds facing a choice between cues released by stressed clone mates and cues released by undisturbed ones. We found that slime moulds actively avoided environments previously explored by stressed clone mates. These results suggest that slime moulds, like bacteria or social amoeba, exhibit physiological responses to biotic and abiotic stresses that can be sensed by conspecifics. Our results establish slime moulds as a promising new model to investigate the use of social information in unicellular organisms. This article is part of the theme issue ‘Signal detection theory in recognition systems: from evolving models to experimental tests’.

Complex population dynamics in a spatial microbial ecosystem with Physarum polycephalum

“…P. polycephalum's slime sheath has also been shown to help clonal P. polycephalum plasmodia navigate their environment. Healthy plasmodia leave behind an attractive stimuli in their slime sheath and stressed Plasmodia leave behind a repellant stimuli in their slime sheath (Briard et al, 2020). We speculate that this slime sheath may have been consumed by microorganisms, just as it has been shown to be consumed by beetles.…”

“…While P. polycephalum is often cited for its capacity to approximate shortest paths between different food sources, there are other facets of its behavior that warrant attention. Briard et al (2020) shows that P. polycephalum slime sheath can provide an attractive or repulsive stimulus depending on the nutritive state of the depositing plasmodia. These can aid in navigation, helping P. polycephalum more robustly navigate its environment in search of food (Boussard et al, 2019).…”

“…By avoiding previously explored areas plasmodia are more efficiently able to explore their environment and navigate around obstacles through a process of elimination (unproductive paths are entombed by P. polycephalum's slime sheath). Briard et al (2020) discusses the topic of external memory and its relationship to slime mold's deposition of its extracellular slime sheath. The observations in (Briard et al, 2020) offer new insights into the role of slime sheaths.…”

“…Briard et al (2020) discusses the topic of external memory and its relationship to slime mold's deposition of its extracellular slime sheath. The observations in (Briard et al, 2020) offer new insights into the role of slime sheaths. In this work, the authors demonstrate that not all slime sheaths serve as an avoidant signal to other conspecific/clonal plasmodia.…”

“…It is possible that a similar feedback loop could be created when P. polycephalum consumes the red yeast. Given that (Briard et al, 2020) shows that a well-nourished P. polycephalum deposits an attractive slime sheath, as the plasmodia migrate in the environment and consume yeast, it might tend to leave more attractive slime sheath nearby sites of yeast predation. This site of slime sheath deposition could be consumed by the red yeast and serve as a future attractive stimulus.…”