Elucidating transmission patterns of endemic Mycobacterium avium subsp. paratuberculosis using molecular epidemiology
Mitchell, Rebecca M. ; Beaver, Annabelle ; Knupfer, Elena ; Pradhan, Abani K. ; Fyock, Terry ; Whitlock, Robert H. ; Schukken, Ynte H. - \ 2019
Veterinary Sciences 6 (2019)1. - ISSN 2306-7381
MLSSR typing - Mutation rate - Mycobacterial co-infections - Mycobacterium avium subsp. paratuberculosis (MAP) - Vertical transmission - Within-host evolution
Mycobacterial diseases are persistent and characterized by lengthy latent periods. Thus, epidemiological models require careful delineation of transmission routes. Understanding transmission routes will improve the quality and success of control programs. We aimed to study the infection dynamics of Mycobacterium avium subsp. paratuberculosis (MAP), the causal agent of ruminant Johne's disease, and to distinguish within-host mutation from individual transmission events in a longitudinally MAP-defined dairy herd in upstate New York. To this end, semi-annual fecal samples were obtained from a single dairy herd over the course of seven years, in addition to tissue samples from a selection of culled animals. All samples were cultured for MAP, and multi-locus short-sequence repeat (MLSSR) typing was used to determine MAP SSR types. We concluded from these precise MAP infection data that, when the tissue burden remains low, the majority of MAP infections are not detectable by routine fecal culture but will be identified when tissue culture is performed after slaughter. Additionally, we determined that in this herd vertical infection played only a minor role in MAP transmission. By means of extensive and precise longitudinal data from a single dairy herd, we have come to new insights regarding MAP co-infections and within-host evolution.
Facilitators of adaptation and antifungal resistance mechanisms in clinically relevant fungi
Hokken, Margriet W.J. ; Zwaan, B.J. ; Melchers, W.J.G. ; Verweij, P.E. - \ 2019
Fungal Genetics and Biology 132 (2019). - ISSN 1087-1845
Adaptation - Antifungal compounds - Antifungal resistance mechanisms - Aspergillus spp. - Candida spp. - Cryptococcus spp. - Mutation rate - Reproduction
Opportunistic fungal pathogens can cause a diverse range of diseases in humans. The increasing rate of fungal infections caused by strains that are resistant to commonly used antifungals results in difficulty to treat diseases, with accompanying high mortality rates. Existing and newly emerging molecular resistance mechanisms rapidly spread in fungal populations and need to be monitored. Fungi exhibit a diversity of mechanisms to maintain physiological resilience and create genetic variation; processes which eventually lead to the selection and spread of resistant fungal pathogens. To prevent and anticipate this dispersion, the role of evolutionary factors that drive fungal adaptation should be investigated. In this review, we provide an overview of resistance mechanisms against commonly used antifungal compounds in the clinic and for which fungal resistance has been reported. Furthermore, we aim to summarize and elucidate potent generators of genetic variability across the fungal kingdom that aid adaptation to stressful environments. This knowledge can lead to recognizing potential niches that facilitate fast resistance development and can provide leads for new management strategies to battle the emerging resistant populations in the clinic and the environment.
Rates of Lateral Gene Transfer in Prokaryotes : High but Why?
Vos, Michiel ; Hesselman, M.C. ; Beek, T.A. te; Passel, M.W.J. van; Eyre-Walker, Adam - \ 2015
Trends in Microbiology 23 (2015)10. - ISSN 0966-842X - p. 598 - 605.
Accessory genome - Distribution of fitness effects - Gene content - Gene loss - Lateral gene transfer - Mutation rate
Lateral gene transfer is of fundamental importance to the evolution of prokaryote genomes and has important practical consequences, as evidenced by the rapid dissemination of antibiotic resistance and virulence determinants. Relatively little effort has so far been devoted to explicitly quantifying the rate at which accessory genes are taken up and lost, but it is possible that the combined rate of lateral gene transfer and gene loss is higher than that of point mutation. What evolutionary forces underlie the rate of lateral gene transfer are not well understood. We here use theory developed to explain the evolution of mutation rates to address this question and explore its consequences for the study of prokaryote evolution.
Effects of spontaneous mutation accumulation on sex ratio traits in a parasitoid wasp
Pannebakker, Bart A. ; Halligan, Daniel L. ; Reynolds, K.T. ; Ballantyne, Gavin A. ; Shuker, David M. ; Barton, Nick H. ; West, Stuart A. - \ 2008
Evolution 62 (2008)8. - ISSN 0014-3820 - p. 1921 - 1935.
Mutation effect - Mutation rate - Nasonia vitripennis - Parasitoid wasp - Sex allocation
Sex allocation theory has proved extremely successful at predicting when individuals should adjust the sex of their offspring in response to environmental conditions. However, we know rather little about the underlying genetics of sex ratio or how genetic architecture might constrain adaptive sex-ratio behavior. We examined how mutation influenced genetic variation in the sex ratios produced by the parasitoid wasp Nasonia vitripennis. In a mutation accumulation experiment, we determined the mutability of sex ratio, and compared this with the amount of genetic variation observed in natural populations. We found that the mutability (h2m) ranges from 0.001 to 0.002, similar to estimates for life-history traits in other organisms. These estimates suggest one mutation every 5-60 generations, which shift the sex ratio by approximately 0.01 (proportion males). In this and other studies, the genetic variation in N. vitripennis sex ratio ranged from 0.02 to 0.17 (broad-sense heritability, H2). If sex ratio is maintained by mutation-selection balance, a higher genetic variance would be expected given our mutational parameters. Instead, the observed genetic variance perhaps suggests additional selection against sex-ratio mutations with deleterious effects on other fitness traits as well as sex ratio (i.e., pleiotropy), as has been argued to be the case more generally.