Confirmation and variability of the Allee effect in Dictyostelium discoideum cell populations, possible role of chemical signaling within cell clusters

Abstract

In studies of the unicellular eukaryote Dictyostelium discoideum, many have anecdotally observed that cell dilution below a certain "threshold density” causes cells to undergo a period of slow growth (lag). However, little is documented about the slow growth phase and the reason for different growth dynamics below and above this threshold density. In this paper, we extend and correct our earlier work to report an extensive set of experiments, including the use of new cell counting technology, that set this slow-to-fast growth transition on a much firmer biological basis. We show that dilution below a certain density (around 10E4 cells/ml) causes cells to grow slower on average and exhibit a large degree of variability: sometimes a sample does not lag at all, while sometimes it takes many moderate density cell cycle times to recover back to fast growth. We perform conditioned media experiments to demonstrate that a chemical signal mediates this endogenous phenomenon. Finally, we argue that while simple models involving fluid transport of signal molecules or cluster-based signaling explain typical behavior, they do not capture the high degree of variability between samples but nevertheless favor an intra-cluster mechanism.

Pleiotropic regulation of bacterial toxin production and Allee effect govern microbial predator–prey interactions

“…(Fadai et al, 2020;Stephens et al, 1999;Teixeira Alves and Hilker, 2017) Previous studies have shown the influence of Allee effects on amoebae−bacteria interactions. (DiSalvo et al, 2014;Rubin et al, 2019;Segota et al, 2022) However, the circumstances in which amoebae could overcome the potent evasion strategies of bacteria remain poorly understood.…”

“…For the social microbe, D. discoideum the Allee effect can be observed both during the vegetative and aggregation stages of its life cycle. (Hashimoto et al, 1975;Segota et al, 2022) Pseudomonas fluorescens HKI0770 is a soil bacterium known to secrete extracellular amoebicidal natural products -pyreudiones (pys) -enabling the bacteria to evade predation. (Klapper et al, 2016) However, a mutant unable to produce pyreudiones is palatable to amoeba.…”