Phenotypic and Gene Expression Changes among Clonal Type I Strains of Toxoplasma gondii

Abstract

Toxoplasma gondii has an unusual population structure consisting of three clonal lineages that predominate in North America and Europe. This simple pattern has encouraged the use of only a few laboratory isolates that are representative of each lineage. Principle among these is the type I RH strain, originally isolated from a child with encephalitis some 70 years ago. Comparison of different passages of the RH strain that have been propagated differently over the intervening time period revealed that the commonly used clonal line called RH-ERP was not representative of natural isolates of the type I lineage. Notably, RH-ERP formed much larger plaques than other type 1 strains, including a separate, earlier derived isolate of the RH strain. The RH-ERP variant also showed enhanced extracellular survival, faster growth, and decreased differentiation compared to the prototype type I strain GT1. Comparison of gene expression differences in the RH-ERP line revealed that several ABC transporters were upregulated, which may provide a growth advantage in vitro. These findings illustrate that dramatic phenotypic changes can arise in laboratory strains, emphasizing the need for comparison with recent clinical isolates.

Virulence differences in Toxoplasma mediated by amplification of a family of polymorphic pseudokinases

“…Although this difference was mapped in the type I strains GT-1, here, we have disrupted the entire locus in the related type I strain RH and observed a strong phenotype consistent with the expected mapping data. Despite small differences previously identified among type I strains (26), these findings argue that ROP5 likely plays a similar important role in the virulence of all type I strains. The ROP5 locus mapped here also corresponds to that previously identified in the cross between types II and III, denoted VIR1 (15), and also, an accompanying report (27) confirms that ROP5 also contributes to virulence differences between types II and III.…”

Phosphorylation of eukaryotic initiation factor-2α promotes the extracellular survival of obligate intracellular parasite Toxoplasma gondii

“…Consistent with their quiescent nature, latent bradyzoites maintain TgIF2α in its phosphorylated state, and it was suggested that this stress response may also function to lower protein synthesis and conserve resources in the dormant parasitic cyst (8). The TgIF2α-S71A mutant was created in the hypervirulent RH type I strain of Toxoplasma; although well suited to study the proliferate stage, the strain has largely lost its ability to develop into bradyzoites in vitro and in vivo (3). To further examine the role of TgIF2α phosphorylation in bradyzoites, it is important to generate the TgIF2α-S71A mutant in type II strain Toxoplasma.…”

“…Tachyzoites remain viable for only a limited time outside of the host cell; the ability of freshly egressed parasites to infect a new host cell monolayer drops significantly between 6 and 12 h of exposure to the extracellular environment (3). The mechanisms the parasite may invoke to cope with the extracellular environment while it searches for a new host cell are not known.…”

AMA1-Deficient Toxoplasma gondii Parasites Transiently Colonize Mice and Trigger an Innate Immune Response That Leads to Long-Lasting Protective Immunity

“…To detect cells that hosted parasites, we used RH green fluorescent protein (GFP ϩ )-AMA1 ϩ (ϭ GFP ϩ -AMA1 ϩ ) tachyzoites as controls because they are fluorescent and their survival rate in mice was previously described as being of the same range as that seen with the RH⌬hxgprt:⌬ku80::diCre strain (8). Nonimmune cells and tissueresident macrophages as well as inflammatory monocytes and neutrophils were recognized using combinatory sets of antibodies directed against surface proteins that commonly served as cell subset markers (see Materials and Methods).…”

“…Within the type I strains defined as uniformly virulent in mice, the RH strain, unlike the GT1 genotype, is commonly reported as unable to form persistent cysts in mice (6,7), although this inability might be the consequence of extensive passages in laboratories (8).…”