Genotyping and Descriptive Proteomics of a Potential Zoonotic Canine Strain of Giardia duodenalis, Infective to Mice

Abstract

The zoonotic potential of giardiasis, as proposed by WHO since the late 70's, has been largely confirmed in this century. The genetic assemblages A and B of Giardia duodenalis are frequently isolated from human and canine hosts. Most of the assemblage A strains are not infective to adult mice, which can limit the range of studies regarding to biology of G. duodenalis, including virulence factors and the interaction with host immune system. This study aimed to determine the infectivity in mice of an assemblage A Giardia duodenalis strain (BHFC1) isolated from a dog and to classify the strain in sub-assemblages (AI, AII, AIII) through the phylogenetic analysis of beta-giardin (bg), triose phosphate isomerase (tpi) and glutamate dehydrogenase (gdh) genes. In addition, the proteomic profile of soluble and insoluble protein fractions of trophozoites was analyzed by 2D-electrophoresis. Accordingly, trophozoites of BHFC1 were highly infective to Swiss mice. The phylogenetic analysis of tpi and gdh revealed that BHFC1 clustered to sub-assemblage AI. The proteomic map of soluble and insoluble protein fractions led to the identification of 187 proteins of G. duodenalis, 27 of them corresponding to hypothetical proteins. Considering both soluble and soluble fractions, the vast majority of the identified proteins (n = 82) were classified as metabolic proteins, mainly associated with carbon and lipid metabolism, including 53 proteins with catalytic activity. Some of the identified proteins correspond to antigens while others can be correlated with virulence. Besides a significant complementation to the proteomic data of G. duodenalis, these data provide an important source of information for future studies on various aspects of the biology of this parasite, such as virulence factors and host and pathogen interactions.

Fig 1. Consensus phylogenetic relationships of G. duodenalis with Bayesian posterior probabilities using a Markov chain Monte Carlo sampling technique, for bg, tpi, and gdh gene sequences of G. duodenalis.

Markov chains were run for 6,000,000 iterations and the trees were sampled every 100 iterations. The GTR model was used with gamma correction. Sequences from Giardia muris, Giardia microti and Giardia ardeae were employed as outgroups.

Fig 2. 2D protein map showing the spots of the soluble protein fraction (Proteins 1 to 429) and the numerical distribution of localized proteins.

The protein identification correspondent to each number is shown in S3 Table.

Fig 3. 2D protein map showing the spots of the insoluble fraction (Proteins 430 to 903) and the numerical distribution of localized proteins.

The protein identification correspondent to each number is shown in S3 Table.

Fig 4. Classification of the identified proteins by molecular function (A), biological process (B) and protein class (C).

This classification is suggested by gene ontology and Panther^® and provides a general characterization of a group of proteins. The numbers presented in each graph correspond to the number of proteins.