Characterization of a mitochondrion-like organelle inCryptosporidium parvum

Abstract

Cryptosporidium parvum is a protozoan parasite that causes widespread diarrhoeal disease in humans and other animals and is responsible for large waterborne outbreaks of cryptosporidiosis. Unlike many organisms belonging to the phylum Apicomplexa, such as Plasmodium spp. and Toxoplasma gondii, there is no clinically proven drug treatment against this parasite. Aspects of the basic biology of C. parvum remain poorly understood, including a detailed knowledge of key metabolic pathways, its genome organization and organellar complement. Previous studies have proposed that C. parvum lacks a relic plastid organelle, or 'apicoplast', but that it may possess a mitochondrion. Here we characterize a mitochondrion-like organelle in C. parvum by (i) ultrastructural and morphological description (ii) localization of heterologous mitochondrial chaperonin antibody probes (iii) phylogenetic analysis of genes encoding mitochondrial transport proteins (iv) identification and analysis of mitochondrion-associated gene sequences. Our descriptive morphological analysis was performed by energy-filtering transmission electron microscopy (EFTEM) of C. hominis and C. parvum. The 'mitochondrion-like' organelle was characterized by labelling the structure with a heterologous mitochondrial chaperonin probe (hsp60) both in immunoelectron microscopy (IMEM) and immunofluorescence (IMF). Phylogenetic analysis of the mitochondrial import system and housekeeping components (hsp60 and hsp70-dnaK) suggested that the C. parvum mitochondrion-like organelle is likely to have descended from a common ancestral apicomplexan mitochondrion. We also identified a partial cDNA sequence coding for an alternative oxidase (AOX) gene, a component of the electron transport chain which can act as an alternative to the terminal mitochondrial respiratory complexes III and IV, which has not yet been reported in any other member of this phylum. Degenerate primers developed to identify selected mitochondrial genes failed to identify either cytochrome oxidase subunit I, or cytochrome b. Taken together, our data aim to provide new insights into the characterization of this Cryptosporidium organelle and a logical framework for future functional investigation.

Alternative oxidase: an inter-kingdom perspective on the function and regulation of this broadly distributed 'cyanide-resistant' terminal oxidase

“…This organism lives best in a low O 2 intestinal environment and AOX might represent a means of removing localised excess O 2 (Putignani et al 2004). A similar role in marine molluscs has been postulated during metabolic rate reduction, ADP limiting conditions or while the cyt pathway is O 2 saturated as a means of maintaining the intracellular partial pressure of O 2 (PO 2 ) (Abele et al 2007).…”

Lipoic Acid Metabolism in Microbial Pathogens

“…The parasite does contain a highly reduced two-membrane compartment called the mitosome that is thought to have descended from a common ancestral apicomplexan mitochondrion (82,180). This organelle appears to have been retained to carry out a limited number of metabolic functions, such as the synthesis of iron-sulfur clusters (116).…”

Niche metabolism in parasitic protozoa

“…(a) Remodelling mitochondrial function There is now a prevailing consensus that all extant eukaryotes probably contain an organelle(s) of mitochondrial ancestry (Mai et al 1999;Tovar et al 1999Tovar et al , 2003Dyall et al 2000;Katinka et al 2001;van der Giezen et al 2002Williams et al 2002;Hrdy et al 2004;Putignani et al 2004). In Plasmodium, Toxoplasma, many other apicomplexan parasites and most trypanosomatids aerobic mitochondria with a capacity for oxidative phosphorylation are present.…”