Investigating in vivo Mycobacterium avium subsp. paratuberculosis microevolution and mixed strain infections
Alexander Byrne1, Nathalie Bissonnette2, Séverine Ollier2
1Department of Biology, Memorial University of Newfoundland , St. John's, Newfoundland and Labrador, Canada.
Importance:
Johne's disease (JD) is a major problem in dairy animals, and concerns have been raised regarding the association of Mycobacterium avium subsp. paratuberculosis (MAP) with Crohn's disease in humans. MAP is an extremely slow-growing bacterium with low genome evolutionary rates. Certain short sequence repeats (SSR1 and SSR2) in the MAP chromosome are highly variable and evolve at a faster rate than the rest of the chromosome. In the current study, multiple MAP isolates with genetic variations such as single-nucleotide polymorphisms, and more noticeably, diverse SSRs, could simultaneously infect animals. Variations in SSR1 and SSR2 affect the products of the respective genes containing them. Since multiple MAP isolates can infect the same animal and the possibility that the pathogen undergoes further changes within the host due to unstable SSRs, this could provide a compensative mechanism for an otherwise slow-evolving pathogen to increase phenotypic diversity for overcoming host responses.
Insights
Mixed strain infections and microevolution are common in Johne's Disease, caused by Mycobacterium avium subsp. paratuberculosis (MAP). Variations in specific short sequence repeats (SSRs) within MAP influence protein products, potentially impacting infectivity and host immune response.
Area of Science:
- Microbiology
- Genomics
- Veterinary Medicine
Background:
- Johne's Disease (JD), caused by Mycobacterium avium subsp. paratuberculosis (MAP), results in substantial economic losses in the global dairy industry.
- Mixed strain infections (MSI) and within-host microevolution are known to influence pathogen dynamics but are understudied in JD.
- MAP is a slow-growing bacterium with a low genome evolutionary rate, yet its adaptation mechanisms require further investigation.
Purpose of the Study:
- To investigate the prevalence and impact of mixed strain infections (MSI) and microevolution in MAP isolates from JD-affected ruminants.
- To characterize genetic variations within MAP strains, focusing on short sequence repeats (SSRs) and their potential functional consequences.
- To explore the implications of these genetic variations on MAP infectivity and host-pathogen interactions.
Main Methods:
- Whole-genome sequencing of up to 10 MAP isolates from 14 high-shedding JD-affected animals.
- Analysis of single-nucleotide polymorphisms (SNPs) and short sequence repeats (SSRs) to identify genetic diversity within and between isolates.
- In silico prediction of protein structure and function for genes affected by SSR variations.
Main Results:
- Evidence of both MSI and microevolution was found in 12 out of 14 examined animals.
- Short sequence repeats SSR1 and SSR2 exhibited high diversity and homoplasy, affecting the genetic reading frames of ORF1 and ORF2.
- Variations in SSR1 and SSR2 led to altered protein sequences and structures, with ORF1 potentially involved in host immune modulation.
Conclusions:
- MSI and microevolution are prevalent in MAP infections, contributing to genetic diversity within hosts.
- Variable SSRs in MAP, particularly SSR1 and SSR2, represent a key mechanism for rapid adaptation and phenotypic diversification.
- These findings suggest a potential mechanism for MAP to overcome host responses, with implications for disease control and understanding MAP's infectivity.
