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Anaplasma marginale msp1alpha genotypes evolved under positive selection pressure but are not markers for geographic
José de la Fuente1, Ronald A Van Den Bussche, Tulio M Prado
1Department of Veterinary Pathobiology, Oklahoma State University, Stillwater, Oklahoma 74708, USA. jose_delafuente@yahoo.com
Abstract:
Anaplasma marginale (order Rickettsiales, family Anaplasmataceae), a tick-borne pathogen of cattle, is endemic in tropical and subtropical regions of the world. Many geographic isolates of A. marginale occur in the United States and have been identified by major surface protein 1a (MSP1a), which varies in sequence and molecular weight due to different numbers of tandem 28- to 29-amino-acid repeats. The present study was undertaken to examine the genetic variations among isolates of A. marginale obtained during 2001 from infected cattle from east-central Oklahoma, where A. marginale is endemic. The gene and protein sequences of MSP1a and msp4 nucleotide sequences were used to infer the phylogenetic relationships among Oklahoma and New World isolates from Argentina, Brazil, Mexico, and the United States. All 11 A. marginale isolates collected from Oklahoma had different MSP1a sequences but identical MSP4 sequences. The phylogenies of the msp4 sequences of 13 isolates from Oklahoma in comparison with those of 7 Latin American isolates and 12 U.S. isolates by maximum-parsimony (MP) and maximum-likelihood (ML) analyses, with A. centrale and A. ovis sequences used as outgroups, provided strong bootstrap analysis support for a Latin American clade. Isolates of A. marginale from the southern United States (Florida, Mississippi, and Virginia) and the west-central United States (California, Idaho, Illinois, Oregon, Missouri, and Texas) also grouped into two clades. Both clades contained isolates from Oklahoma, suggesting extensive cattle movement. ML analysis of the msp4 sequences of isolates from Oklahoma provided bootstrap analysis support for east-central and north-central clades in Oklahoma, and both clades included isolates from Stillwater, Okla. Analysis of the codon and amino acid changes among the msp4 sequences of isolates with different phylogenies provided evidence that msp4 is not under positive selection pressure. In contrast, the phylogenies of the MSP1a DNA and protein sequences of 13 isolates from Oklahoma in comparison with those of 7 Latin American and 13 isolates from the United States by MP and ML analyses demonstrated no geographic clustering and provided evidence that this gene is under positive selection pressure. The results indicate that msp1alpha is not a marker for the characterization of A. marginale geographic isolates and suggest that the genetic heterogeneity observed among isolates of A. marginale within Oklahoma could be explained by cattle movement and the maintenance of different genotypes by independent transmission events.
Insights
Genetic analysis of Anaplasma marginale isolates in Oklahoma reveals significant variation in the major surface protein 1a (MSP1a) gene, while the msp4 gene shows less diversity. Cattle movement likely drives the observed genetic heterogeneity of this important cattle pathogen.
Area of Science:
- Veterinary Microbiology
- Molecular Epidemiology
- Bovine Pathogens
Background:
- Anaplasma marginale is a tick-borne cattle pathogen prevalent globally.
- Geographic isolates of A. marginale exhibit genetic variation, particularly in the major surface protein 1a (MSP1a) gene, due to repeat number differences.
Purpose of the Study:
- To investigate genetic variations among Anaplasma marginale isolates from east-central Oklahoma.
- To infer phylogenetic relationships using MSP1a and msp4 gene sequences.
Main Methods:
- Phylogenetic analysis using maximum-parsimony (MP) and maximum-likelihood (ML) methods.
- Comparison of nucleotide sequences of MSP1a and msp4 genes from Oklahoma, Latin American, and other U.S. isolates.
- Analysis of codon and amino acid changes to assess selection pressure.
Main Results:
- All 11 Oklahoma A. marginale isolates had distinct MSP1a sequences but identical MSP4 sequences.
- Phylogenetic analysis of msp4 revealed a Latin American clade and distinct U.S. clades, with Oklahoma isolates distributed across them.
- MSP1a phylogenies showed no geographic clustering, indicating positive selection, while msp4 showed no positive selection pressure.
Conclusions:
- The msp4 gene provides a reliable marker for characterizing geographic isolates of A. marginale.
- The MSP1a gene is not suitable for characterizing geographic isolates due to high variability and positive selection.
- Genetic heterogeneity within Oklahoma is likely driven by cattle movement and independent transmission events.