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Published on: September 27, 2018
Identification and characterization of a spore-like morphotype in chronically starved Mycobacterium avium subsp.
Elise A Lamont1, John P Bannantine, Aníbal Armién
1Veterinary Population Medicine, University of Minnesota, St. Paul, Minnesota, United States of America.
Abstract:
Mycobacteria are able to enter into a state of non-replication or dormancy, which may result in their chronic persistence in soil, aquatic environments, and permissive hosts. Stresses such as nutrient deprivation and hypoxia provide environmental cues to enter a persistent state; however, a clear definition of the mechanism that mycobacteria employ to achieve this remains elusive. While the concept of sporulation in mycobacteria is not novel, it continues to spark controversy and challenges our perceptions of a non-replication. We investigated the potential role of sporulation in one-year old broth cultures of Mycobacterium subsp. paratuberculosis (MAP). We show that dormant cultures of MAP contain a mix of vegetative cells and a previously unknown morphotype resembling a spore. These spore-like structures can be enriched for using sporulating media. Furthermore, purified MAP spore forms survive exposure to heat, lysozyme and proteinase K. Heat-treated spores are positive for MAP 16SrRNA and IS900. MAP spores display enhanced infectivity as well as maintain acid-fast characteristics upon germination in a well-established bovine macrophage model. This is the first study to demonstrate a new MAP morphotype possessing spore-like qualities. Data suggest that sporulation may be a viable mechanism by which MAP accomplishes persistence in the host and/or environment. Thus, our current understanding of mycobacterial persistence, pathogenesis, epidemiology and rational drug and vaccine design may need to be reevaluated.
Insights
Mycobacterium subsp. paratuberculosis (MAP) may form spores, a previously unknown dormant state. These MAP spores exhibit enhanced survival and infectivity, potentially explaining chronic persistence in hosts and environments.
Area of Science:
- Microbiology
- Cell Biology
- Infectious Diseases
Background:
- Mycobacteria can enter dormant states, enabling chronic persistence in various environments.
- The exact mechanisms of mycobacterial dormancy, including potential sporulation, remain poorly understood.
- Mycobacterium subsp. paratuberculosis (MAP) persistence is a significant challenge in host and environmental settings.
Purpose of the Study:
- To investigate the potential role of sporulation in long-term dormant cultures of MAP.
- To characterize a novel morphotype observed in dormant MAP cultures.
- To assess the survival and infectivity of this putative MAP spore form.
Main Methods:
- Culturing MAP for one year to induce dormancy.
- Enrichment of spore-like structures using sporulating media.
- Assessing survival of purified spore forms against heat, lysozyme, and proteinase K.
- Germination and infectivity assays in a bovine macrophage model.
Main Results:
- Dormant MAP cultures contained a mix of vegetative cells and a novel spore-like morphotype.
- These spore-like structures were enriched in sporulating media.
- Purified MAP spores demonstrated resistance to heat, lysozyme, and proteinase K.
- MAP spores showed enhanced infectivity and maintained acid-fastness upon germination in macrophages.
Conclusions:
- A novel MAP morphotype with spore-like characteristics has been identified.
- Sporulation may be a key mechanism for MAP persistence in hosts and the environment.
- These findings necessitate a reevaluation of mycobacterial persistence, pathogenesis, and therapeutic strategies.
