Submitted to: PLoS One
Publication Type: Peer reviewed journal
Publication Acceptance Date: 12/20/2011
Publication Date: 1/24/2012
Citation: Lamont, E.A., Bannantine, J.P., Armien, A., Ariyakumar, D.S., Sreevatsan, S. 2012. Identification and characterization of a spore-like morphotype in chronically starved Mycobacterium avium subsp. paratuberculosis cultures. PLoS One [serial online]. 7(1):e30648. Available: http://www.plosone.org/article/info%3Adoi%2F10.1371%2Fjournal.pone.0030648. Interpretive Summary: This study was performed to document a unique observation for M. avium subspecies paratuberculosis (bacterium causing Johne’s disease). Under conditions in which the bacterium ages or is deprived of nutrition, it develops spore-like structures. In additions, these spore-like forms show heat resistance. This novel finding may explain the persistence observed in this long and protracted disease of cattle.
Technical Abstract: Background 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). Results We show that dormant cultures of MAP contain a mix of vegetative cells and spores that can be enriched for spores using sporulating media. Furthermore, purified MAP spores 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. Conclusions This is the first study to demonstrate sporulation in MAP. 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.