Comparative tachyzoite proteome analyses among six Neospora caninum isolates with different virulence.

The biological variability among Neospora caninum isolates has been widely shown, however, the molecular basis that determines this diversity has not been thoroughly elucidated to date. The latest studies have focused on a limited number of isolates. Therefore, the goal of the present study was to compare the proteome of a larger number of N. caninum isolates with different origins and virulence. Label-free LC-MS/MS was used to investigate the tachyzoite proteomic differences among Nc-Bahia, Nc-Spain4H and Nc-Spain7, representing high virulence isolates and Nc-Ger6, Nc-Spain2H and Nc-Spain1H, representing low virulence isolates. Pairwise comparisons between all isolates and between high virulence and low virulence groups identified a subset of proteins with higher abundance in high virulence isolates. These proteins were involved in energy and redox metabolism, and DNA/RNA processing, which might determine the faster growth rates and parasite survival of the high virulence isolates. Highlighted proteins included a predicted member of the rhoptry kinase family ROP20 specific for N. caninum, Bradyzoite pseudokinase 1 and several dense granule proteins. DNA polymerase, which was more abundant in all high virulence isolates in all comparisons, might also be implicated in virulence. These results reveal insights into possible mechanisms involved in specific phenotypic traits and virulence in N. caninum, and the relevance of these candidate proteins for N. caninum virulence deserves further investigation.