The Ultra‐Structural Similarities between Cryptosporidium parvum and the Gregarines

Abstract

Using a transmission electron microscopy-based approach, this study details the striking similarities between Cryptosporidium parvum and the gregarines during in vitro axenic development at high ultra-structural resolution. C. parvum zoites displayed three unusual regions within uninucleated parasites: epimerite-like, protomerite-like, and the cell body; these regions exhibited a high degree of morphological similarity to gregarine-like trophozoites. The presence of a mucron-like bulging structure at the side of the free ovoid gregarine-like zoites was observed after 2 h of cultivation. An irregular pattern of epicytic-like folds were found to cover the surface of the parasites 24 h postcultivation. Some extracellular stages were paired in laterocaudal or side-side syzygy, with the presence of a fusion zone between some of these zoites. The present findings are in agreement with phylogenetic studies that have proposed a sister relationship with gregarines. Cryptosporidium appears to exhibit tremendous variety in cell structure depending on the surrounding environment, thereby mimicking the "primitive" gregarines in terms of the co-evolution strategy between the parasites and their environments. Given this degree of similarity, different aspects of the evolutionary biology of Cryptosporidium need to be examined, considering the knowledge gained from the study of gregarines.

Life without a Host Cell: What is Cryptosporidium ?

“…This is reflected in the new classification proposed by Cavalier-Smith [21] where Cryptosporidium, which is the only gregarine parasitic in vertebrates, has been placed in a class of its own. [6,14,17,20], and a greater degree of pleomorphism than reported previously, particularly of gamonts and gamont-like stages [11,20,21,26], all of which are gregarine characteristics. Of particular significance are observations from both in vitro and in vivo studies that, in addition to epicellular multiplication, Cryptosporidium can also complete its life cycle without apparent epicellular attachment with host cells (Figure 1, Key Figure) [6][7][8]10,12,18,20].…”

“…Table I summarizes the features that Cryptosporidium shares with gregarines. There are striking similarities both structurally and in feeding behavior between Cryptosporidium and gregarines [11,14,20,26]. Conversely, Cryptosporidium is unusual compared with other gregarines with regard to its diverse and broad host range and its close association with the host cell, which is epicellular (intracellular but extracytoplasmic) [25].…”

“…The studies of Carreno et al [5] using 18S sequencing demonstrated a closer phylogenetic relationship to gregarine protozoa than to coccidians and these have since been complemented by observations of Cryptosporidium's developmental biology and metabolism (Box 1) [6][7][8][9][10][11][12][13][14][15][16][17][18][19][20]. In particular, the initial controversial images and theories of Hijjawi et al [6] and Karanis et al [10], which showed that Cryptosporidium oocysts, like gregarines, could excyst and produce pleomorphic (see Glossary) stages without host cells or triggers, were widely disputed within the Cryptosporidium research community.…”

Waterborne Giardia and Cryptosporidium: contamination of human drinking water by sewage and cattle feces

“…However, recent phylogenetic studies have shown closer proximity of Cryptosporidium with gregarine protozoan than with coccidia, because they have a feeding organelle and absence of apicoplast, which allowed their reclassification in the Gregarinomorphea class, Cryptogregaria subclass (KOH et al, 2013(KOH et al, , 2014CAVALIER-SMITH, 2014;HUANG et al, 2014;CLODE et al, 2015;ALDEYARBI;RYAN et al, 2016).…”

A cell culture platform forcryptosporidiumthat enables long-term cultivation and new tools for the systematic investigation of its biology

“…It is caused by species of the genus Cryptosporidium, in humans typically by C. parvum and C. hominis. The Cryptosporidium species belong to the phylum Apicomplexa and it has recently been proposed for the species to be reclassified as a member of the subclass of gregarina 5,6 . They are waterborne pathogens, and cryptosporidiosis has commonly been associated with disease in developing countries [7][8][9] .…”