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Open Access Research article

Global proteomic analysis of the oocyst/sporozoite of Toxoplasma gondii reveals commitment to a host-independent lifestyle

Alessia Possenti1, Federica Fratini1, Luca Fantozzi3, Edoardo Pozio1, Jitender P Dubey2, Marta Ponzi1, Elisabetta Pizzi1 and Furio Spano1*

Author Affiliations

1 Department of Infectious, Parasitic and Immunomediated Diseases, Istituto Superiore di Sanità, Viale Regina Elena 299, Rome 00161, Italy

2 United States Department of Agriculture, Agricultural Research Service, Animal Parasitic Diseases Laboratory, Animal and Natural Resources Institute, Beltsville, MD, 20705, USA

3 Present address: Agenzia Regionale per la Protezione Ambientale del Lazio, Sezione di Rieti, Via Salaria per l'Aquila 8, Rieti, 02100, Italy

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BMC Genomics 2013, 14:183  doi:10.1186/1471-2164-14-183

Published: 15 March 2013

Abstract

Background

Toxoplasmosis is caused by the apicomplexan parasite Toxoplasma gondii and can be acquired either congenitally or via the oral route. In the latter case, transmission is mediated by two distinct invasive stages, i.e., bradyzoites residing in tissue cysts or sporozoites contained in environmentally resistant oocysts shed by felids in their feces. The oocyst plays a central epidemiological role, yet this stage has been scarcely investigated at the molecular level and the knowledge of its expressed proteome is very limited.

Results

Using one-dimensional gel electrophoresis coupled to liquid chromatography-linked tandem mass spectrometry, we analysed total or fractionated protein extracts of partially sporulated T. gondii oocysts, producing a dataset of 1304 non reduntant proteins (~18% of the total predicted proteome), ~59% of which were classified according to the MIPS functional catalogue database. Notably, the comparison of the oocyst dataset with the extensively covered proteome of T. gondii tachyzoite, the invasive stage responsible for the clinical signs of toxoplasmosis, identified 154 putative oocyst/sporozoite-specific proteins, some of which were validated by Western blot. The analysis of this protein subset showed that, compared to tachyzoites, oocysts have a greater capability of de novo amino acid biosynthesis and are well equipped to fuel the Krebs cycle with the acetyl-CoA generated through fatty acid β-oxidation and the degradation of branched amino acids.

Conclusions

The study reported herein significantly expanded our knowledge of the proteome expressed by the oocyst/sporozoite of T. gondii, shedding light on a stage-specifc subset of proteins whose functional profile is consistent with the adaptation of T. gondii oocysts to the nutrient-poor and stressing extracellular environment.

Keywords:
Toxoplasma gondii; Oocyst; Sporozoite; Proteome; Metabolism; Energy production; Host cell invasion; Oocyst-specific proteins