By Avelina Espinosa & Guillermo Paz-y-Miño-C

Our latest review on clone-clone discrimination/recognition in Entamoeba species has been featured on the cover of the Journal of Eukaryotic Microbiology (JEUK-MIC, Volume 66, Issue 2, March-April 2019). This is the second time our work has made it to the cover of JEUK-MIC (the first time was back in 2012, coincidentally in the March-April Volume 59, Issue 2). Below are the links to the 2019 article, as well as the abstract and caption to the cover image.

Discrimination Experiments In Entamoeba and Evidence from other Protists Suggest Pathogenic Amebas Cooperate with Kin to Colonize Hosts and Deter Rivals. 2019. Avelina Espinosa & Guillermo Paz-y-Miño-C. Journal of Eukaryotic Microbiology 66(2): 354–368.

Entamoeba histolytica is one of the least understood protists in terms of taxa-, clone- and kin-discrimination/recognition ability. Yet, the capacity to tell apart same or self (clone/kin) from different or non-self (non-clone/non-kin) has long been demonstrated in pathogenic eukaryotes like Trypanosoma and Plasmodium, free-living social amebas (Dictyostelium, Polysphondylium), budding yeast (Saccharomyces), and in numerous bacteria and archaea (prokaryotes). Kin discrimination/recognition is explained under inclusive fitness theory; that is, the reproductive advantage that genetically closely related organisms (kin) can gain by cooperating preferably with one another (rather than with distantly related or unrelated individuals), minimizing antagonism and competition with kin, and excluding genetic strangers (or cheaters = non-cooperators that benefit from others’ investments in altruistic cooperation). In this review, we rely on the outcomes of in vitro pairwise discrimination/recognition encounters between seven Entamoeba lineages to discuss the biological significance of taxa-, clone- and kin-discrimination/recognition in a range of generalist and specialist species (close or distantly related phylogenetically). We then focus our discussion on the importance of these laboratory observations for E. histolytica‘s life cycle, host infestation, and implications of these features of the amebas’ natural history for human health (including mitigation of amebiasis).

About the Cover (above): Population bottlenecks (PB) in the life cycle of Entamoeba histolytica. (1) Upon host’s ingestion of contaminated food and water, ameba-cysts (dormant stage of the organism) will face the enzymatic milieu of the oral cavity (the mouth environment can be highly variable in temperature, concentration and mix of chemicals originated from diverse foods and the host’s own microbiota); (2) once reaching the stomach, the cysts will be exposed to high acidity, an inducer of severe ameba-cysts-population crashes; (3) cysts arrival at the small intestine, a more favorable environment for excystation; (4) not all amebas released during excystation will survive (simply due to intrinsic differential survival); (5) the colonization of the mucous layer on the small-intestine endothelium (nutrient-rich) will induce fast ameba clonal proliferation, but the successful population expansion will depend on variable conditions inside the host and be limited by the presence of different clone competitors (priority effects, see text); (5a) a potential trophozoite invasion of the colon in the large intestine (if it occurs) will be countered by the host’s immune responses (i.e. endothelium guarded by white-blood cells) and also by other ameba clones already established in the colon; (5b) in the uncommon cases of systemic infection, the liver, lungs and other organs (rarely the brain) can be colonized by amebas, which form abscesses, but abscess formation involves high mortality (both caused by host immunity and amebas’ own programmed cell death, PCD, imposed by abscess development); (from 5 to 6) prior to being eliminated from the body, the amebas must encyst, but not all cells will successfully form cysts; (7) and (8) cysts released into the external environment will face additional population crashes, although not directly associated with the fate of the host. To overcome the challenges of population demise (PBs) and stochastic opportunities to recover inside the host, amebas will need to associate and cooperate with clone members (kin); single amebas will not survive and associations or cooperation with genetic strangers will be maladaptive (prone to cheating). Dotted line indicates cases of direct elimination of cysts from the small intestine. ‒ EvoLiteracy © 2019

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