Decay of the glycolytic pathway and adaptation to intranuclear parasitism within Enterocytozoonidae microsporidia

Abstract

Glycolysis and oxidative phosphorylation are the fundamental pathways of ATP generation in eukaryotes. Yet in microsporidia, endoparasitic fungi living at the limits of cellular streamlining, oxidative phosphorylation has been lost: energy is obtained directly from the host or, during the dispersive spore stage, via glycolysis. It was therefore surprising when the first sequenced genome from the Enterocytozoonidae - a major family of human and animal-infecting microsporidians - appeared to have lost genes for glycolysis. Here, we sequence and analyse genomes from additional members of this family, shedding new light on their unusual biology. Our survey includes the genome of Enterocytozoon hepatopenaei, a major aquacultural parasite currently causing substantial economic losses in shrimp farming, and Enterospora canceri, a pathogen that lives exclusively inside epithelial cell nuclei of its crab host. Our analysis of gene content across the clade suggests that Ent. canceri's adaptation to intranuclear life is underpinned by the expansion of transporter families. We demonstrate that this entire lineage of pathogens has lost glycolysis and, uniquely amongst eukaryotes, lacks any obvious intrinsic means of generating energy. Our study provides an important resource for the investigation of host-pathogen interactions and reductive evolution in one of the most medically and economically important microsporidian lineages.

Evolution of microsporidia: An extremely successful group of eukaryotic intracellular parasites

“…To the right of each species are illustrations of the host(s) that each species has been reported to infect. This phylogenetic tree is largely in agreement with recent previously published phylogenies [3,4,8,9,19,23,27], with the exception of Anncaliia algerae or Edhazardia aedis, which have different placements in several reports [3,8,23,27]. (B) Comparision of protein content for each species.…”

“…Although all microsporidia species have lost many metabolic enzymes, there are important distinctions such as differential losses in lipid biosynthesis genes [3]. Additionally, Enterocytozoon species have lost genes necessary for glycolysis, leaving them completely dependent on their host for energy production [23].…”

“…Of two different species of Nematocida that infect Caenorhabditis elegans, N. parisii only infects the intestine, whereas N. displodere proliferates in several tissues including the muscle and epidermis. Differences in subcellular localization have also been observed, such as with the related crab-infecting species Hepatospora eriocheir and Enterospora canceri, which infect the cytoplasm and nuclei, respectively [23].…”

The invasive cell coat at the microsporidian Trachipleistophora hominis–host cell interface contains secreted hexokinases

“…Comparison to solved structures of Saccharomyces cerevisiae HK PII (HXK2) (Kuser, Krauchenco, Antunes, & Polikarpov, ) revealed conservation of high proportions of functional residues, involved in catalysis, substrate binding, and turnover, as well as enzyme flexibility. As previously reported (Wiredu Boakye et al., ), functional residues in the S. cerevisiae HXK1 (conserved in HXK2 also) active site such as Asp 211 (catalytic base), Thr 234 and Ser 419 (ATP binding), Glu 269 and Glu 302 (glucose binding) are all highly conserved in the T. hominis isoforms HK2 and 3. In addition, we found a high degree of conservation of residues involved in enzyme flexibility (glycines) and of charge in the putative hydrophobic channel (see Table S1).…”

“…We analyzed the protein sequences of T. hominis HKs, identified as already described (Wiredu Boakye et al, 2017). In this paper, we identify four: HK1 (THOM_0443), HK2 (THOM_0898), HK3 (THOM_0937), and HK4 (THOM_1847-8), of which three (HK1, 2, and 3) have N-terminal signal peptides identified using software SignalP and PrediSi (Hiller, Grote, Scheer, Münch, & Jahn, 2004;Petersen, Brunak, von Heijne, & Nielsen, 2011).…”