Vincent Racaniello, Elio Schaechter, Michele Swanson, and Michael Schmidt hosted episode 255 of the podcast “This Week in Microbiology” entitled "Fleaing the Plague.” During the episode, they discussed two papers published in late 2021. The first paper by Kehe et al. focused on positive interactions within microbial communities under varying carbon conditions. Previously, positive interactions between microbes were thought to be rare, having been observed in less than 10% of cases in a previous study2. However, using a kChip to measure interactions between co-cultures of soil bacteria in different carbon conditions where each co-culture consisted of two different bacterial species, one fluorescently labeled and one unlabeled, Kehe et al. discovered that positive interactions accounted for almost half of all interactions. They also found that these interactions were especially frequent between taxonomically and metabolically diverse strains.
Personally, I found the authors’ use of the term “positive interaction” to be a bit misleading, initially thinking that these interactions were mutually beneficial to multiple bacterial strains within a community. However, the authors defined an interaction as positive if growth yield increased only for the labeled bacterial species within a co-culture instead of both the labeled and unlabeled species present. Applying this definition, the authors identified half of the observed positive interactions to be parasitic with a small percentage of commensalistic relationships and an even smaller percentage of mutualistic relationships making up the rest of the positive interactions. Though the classification of interactions was counterintuitive, the study did illustrate the importance of diversity within microbial communities and microbial ecology, which has since led to studies expanding on these interactions such as viral pathogenicity during co-infection3.
The second paper discussed was a study by Bland et al. on the yersinia murine toxin found in Yersinia pestis, the bacteria responsible for plague. While the plague is commonly thought to be a thing of the past, new cases of plague are still reported every year, often contracted through flea bites5. Surprisingly, Y. pestis is a fairly young pathogen, originating less than 6,000 years ago with very few genetic differences from its ancestral bacteria that allowed it to be transmittable by fleas. One such difference was the addition of the yersinia murine toxin (Ymt) gene which increases the survival of Y. pestis when infected blood is taken up by fleas, but only if the blood originated from certain species of mammals, like black rats (R. rattus) as opposed to brown rats (R. norvegicus)4. Bland et al. discovered that the blood biochemistry of some mammals impacted the survival of Y. pestis without the Ymt gene in the flea gut. They determined that Ymt was essential for Y. pestis survival and transmission in fleas as it protects against an antibacterial agent present during flea digestion. This study provided insight into the role of Ymt in the persistence of Y. pestis and the evolutionary and ecological history of “flea-borne plague”4.
Overall, while the two papers appeared to be on very different topics, they both shared a common theme. Both studies highlighted the importance of evolutionary and ecological relationships microbes have developed with each other and with other species. I feel that a deep understanding of these relationships will play a significant role in future studies, particularly those regarding microbiomes, anti-microbial resistance, and viral transmission.
References
- Kehe, J., Ortiz, A., Kulesa, A., Gore, J., Blainey, P. C., & Friedman, J. (2021). Positive interactions are common among culturable bacteria. Science Advances, 7(45), eabi7159. https://doi.org/10.1126/sciadv.abi7159
- Foster, K. R., & Bell, T. (2012). Competition, not cooperation, dominates interactions among culturable microbial species. Current Biology: CB, 22(19), 1845–1850. https://doi.org/10.1016/j.cub.2012.08.005
- Shirley, K., & Loftis, J. M. (2022). A spotlight on HCV and SARS-CoV-2 co-infection and brain function. Pharmacology, Biochemistry, and Behavior, 217, 173403. https://doi.org/10.1016/j.pbb.2022.173403
- Bland, D. M., Miarinjara, A., Bosio, C. F., Calarco, J., & Hinnebusch, B. J. (2021). Acquisition of yersinia murine toxin enabled Yersinia pestis to expand the range of mammalian hosts that sustain flea-borne plague. PLoS Pathogens, 17(10), e1009995. https://doi.org/10.1371/journal.ppat.1009995
- CDC. (2022, November 16). Plague surveillance | CDC. Centers for Disease Control and Prevention. https://www.cdc.gov/plague/maps/index.html
