The evolutionary history of eukaryotes: how the ancestral proto-lineage conserved in hypoxic eukaryotes led to protist pathogenicity

Abstract

The aim and the background of this paper was to investigate how ancient primitive eukaryotes evolved to the successful parasites they are today. In preparing this work, the most significant literature of the last years has been studied. We expand it by the results of our own research. Results and conclusion: Anaerobic single-celled eukaryotes, such as Entamoeba invadens and Giardia lamblia, became successful invasive pathogens by using mechanisms inherited from the common ancestor (LECA). As described in previous papers pathogen protists have a surprising stem cell network (ancient protolineage) controlled by intrinsic and extrinsic mechanisms of cell conversion and differentiation inherited from the ancestor. Mechanisms leading to pathogenicity were not acquired after the organisms became parasitic, they were present before the single-celled organisms switched to parasitism. Only organisms possessing an extended ancestral stem cell system capable of switching between most oxidative (MO) and most hypoxic (MH) niches by changing metabolic pathways and antigenicity could develop into successful invasive pathogens like Entamoeba or Giardia. Related organisms not conserving all ancestral features evolved to become luminal commensals or free-living protists.

Origin of Mutualism Between Termites and Flagellated Gut Protists: Transition From Horizontal to Vertical Transmission

“…Cellulose digestion became a cooperative endeavor after the flagellates were taken into host custody via vertical transmission, pushing flagellates to the mutualism end of the symbiotic spectrum. Parasites are adept at changing metabolic pathways and evolve rapidly in response to new selective pressures (Poulin, 1998;Tachezy and Šmíd, 2008); they have a surprising stem cell network controlled by intrinsic and extrinsic mechanisms of cell conversion and differentiation (Niculescu, 2014). The importance of protists in biogeochemical nutrient cycling in the external environment (Geisen et al, 2017) furthermore suggests that they have a wealth of metabolic capacities that could be exploited by the host.…”

The cell system of Giardia lamblia in the light of the protist stem cell biology

“…The ability to form cysts by different mechanisms distinguishes the secondary ATD cysts producing line s-SRL/ATD from the tertiary t-SRL(ITD) line capable of ITD encystment. In contrast to basal metazoans for example Hydra [11] protist stem cell lines have a well defined stem cell hierarchy and can interconvert one to the other within an integrated lineage (P/S, P/T and S/T conversion) [3,5,6]. Stem cell line conversion in E. invadens is induced by oxidative stress or hypoxia.…”

“…This result can be achieved only by asymmetric divisions (n=3) and expressed a D1 3 :D2 1-3 ratio. D1 3 cells are SRT cells in the 3 rd generation and D2 [1][2][3] are MAT cells from three cell generations. By prolonged cultivation (t24-t72) the MA fraction increased to 80% (t48/ n=4), respectively 83-85% (t72/n=5).…”

“…We hypothesized that the minor fraction of "spontaneous" cysts observed in SAT subpopulations [16,60] is produced by a secondary s-SRL cell line similar with the s-SRL/ATD stem cell line of E. invadens, that encysts by intrinsic mechanisms for autonomous terminal differentiation [3,5,6]. However, axenic growth conditions do not promote the development of a dominant s-SRL cell line for mass encystment.…”

“…Both protists meet the current criteria of ancient stem cells (AnSC). Until recently the origin and the beginning of stemness remains an enigma [2,3]. Before AnSC were discovered in pathogen protists [4][5][6] little is known about the evolutionary origin of stem cells, when stem cells appeared and why.…”