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SummaryTrypanosoma cruzi isolates from 23 acute chagasic patients from localities of Western Venezuela (state of Barinas) where Chagas' disease is endemic were typed using ribosomal and mini-exon gene markers.Results showed that isolates of the two major phylogenetic lineages, T. cruzi I and T. cruzi II, were isolated from these patients. Six isolates (26%) were typed as T. cruzi II and 17 (74%) as belonging to T. cruzi lineage I. Analysis of random amplified polymorphic DNA (RAPD) patterns confirmed these two groups of isolates, but did not disclose significant genetic intra-lineage polymorphism. Patients infected by both T. cruzi I or T. cruzi II showed different clinical profiles presenting highly variable signs and symptoms of acute phase of Chagas' disease ranging from totally asymptomatic to severe heart failure. The predominance of T. cruzi I human isolates in Venezuela allied to the higher prevalence of severe symptoms of Chagas' disease (heart failure) in patients infected by this lineage do not corroborate an innocuousness of T. cruzi I infection to humans. To our knowledge, this is the first study describing predominance of T. cruzi lineage I in a large number of acute chagasic patients with distinct and wellcharacterized clinical profiles.

BackgroundTrypanosomatids of the genera Angomonas and Strigomonas live in a mutualistic association characterized by extensive metabolic cooperation with obligate endosymbiotic Betaproteobacteria. However, the role played by the symbiont has been more guessed by indirect means than evidenced. Symbiont-harboring trypanosomatids, in contrast to their counterparts lacking symbionts, exhibit lower nutritional requirements and are autotrophic for essential amino acids. To evidence the symbiont’s contributions to this autotrophy, entire genomes of symbionts and trypanosomatids with and without symbionts were sequenced here.ResultsAnalyses of the essential amino acid pathways revealed that most biosynthetic routes are in the symbiont genome. By contrast, the host trypanosomatid genome contains fewer genes, about half of which originated from different bacterial groups, perhaps only one of which (ornithine cyclodeaminase, EC:4.3.1.12) derived from the symbiont. Nutritional, enzymatic, and genomic data were jointly analyzed to construct an integrated view of essential amino acid metabolism in symbiont-harboring trypanosomatids. This comprehensive analysis showed perfect concordance among all these data, and revealed that the symbiont contains genes for enzymes that complete essential biosynthetic routes for the host amino acid production, thus explaining the low requirement for these elements in symbiont-harboring trypanosomatids. Phylogenetic analyses show that the cooperation between symbionts and their hosts is complemented by multiple horizontal gene transfers, from bacterial lineages to trypanosomatids, that occurred several times in the course of their evolution. Transfers occur preferentially in parts of the pathways that are missing from other eukaryotes.ConclusionWe have herein uncovered the genetic and evolutionary bases of essential amino acid biosynthesis in several trypanosomatids with and without endosymbionts, explaining and complementing decades of experimental results. We uncovered the remarkable plasticity in essential amino acid biosynthesis pathway evolution in these protozoans, demonstrating heavy influence of horizontal gene transfer events, from Bacteria to trypanosomatid nuclei, in the evolution of these pathways.