Keshavarz Maryam, Franz Mathias, Xie Haicheng, Zanchi Caroline, Mbedi Susan, Sparmann Sarah, Rolff Jens
Evolutionary Biology, Institute of Biology, Freie Universität Berlin, Berlin, Germany.
Berlin Center for Genomics in Biodiversity Research, BeGenDiv, Berlin, Germany.
BMC Biol. 2025 Sep 16;23(1):278. doi: 10.1186/s12915-025-02399-1.
In many animals, survival during infection depends on the ability to coordinate interactions between the host immune system and gut microbiota. These tripartite interactions, in turn, potentially shape pathogen virulence evolution. A key regulator of the immune system and, hence, bipartite interactions in insects is the immune deficiency (Imd) pathway, which modulates gut microbiota and pathogens by synthesizing antimicrobial peptides (AMPs) through the NF-κB transcription factor Relish. However, whether Imd-dependent AMPs mediate indirect interactions between gut microbiota and pathogens in a tripartite context remains unclear. Using RNAi-mediated knockdown of Tenebrio molitor Relish (TmRelish), we hypothesized that Imd-dependent AMPs influence indirect interaction between Providencia burhodogranariea_B (P. b_B) infection and the gut microbiota.
TmRelish knockdown altered bipartite interactions by disrupting gut microbiota load and composition, increasing pathogen load, and ultimately leading to higher host mortality during infection. However, we did not find support for our tripartite hypothesis that Imd-dependent AMPs mediate indirect interactions between the gut microbiota and P. b_B infection, suggesting the involvement of alternative regulatory pathways or Imd-independent mechanisms. Nevertheless, our investigations of tripartite interactions showed a positive effect of P. b_B infection on gut microbiota load, which in turn stimulated the expression of a subset of AMPs. However, this upregulation of AMPs did not result in reduced P. b_B load. Notably, the gut microbiota did not affect pathogen load but promoted host survival during P. b_B infection, indicating a role in increasing host tolerance rather than resistance.
These findings suggest that while Imd-dependent AMPs may not mediate tripartite interactions in our system, microbiota-host interactions, such as microbiota-mediated immune priming and changes in microbiota load, can shape infection outcomes. These effects on infection outcomes almost certainly exert important selective pressures on the evolution of bacterial virulence.
在许多动物中，感染期间的存活取决于协调宿主免疫系统与肠道微生物群之间相互作用的能力。反过来，这些三方相互作用可能会影响病原体毒力的进化。免疫系统的一个关键调节因子，也是昆虫中双方相互作用的关键调节因子，是免疫缺陷（Imd）途径，它通过核因子-κB转录因子Relish合成抗菌肽（AMPs）来调节肠道微生物群和病原体。然而，在三方环境中，依赖Imd的AMPs是否介导肠道微生物群与病原体之间的间接相互作用仍不清楚。通过RNA干扰介导的黄粉虫Relish（TmRelish）基因敲除，我们推测依赖Imd的AMPs会影响普罗维登斯菌_B（P. b_B）感染与肠道微生物群之间的间接相互作用。
TmRelish基因敲除通过破坏肠道微生物群的数量和组成、增加病原体数量，最终导致感染期间宿主死亡率升高，从而改变了双方相互作用。然而，我们没有找到支持我们三方假设的证据，即依赖Imd的AMPs介导肠道微生物群与P. b_B感染之间的间接相互作用，这表明可能涉及其他调节途径或不依赖Imd的机制。尽管如此，我们对三方相互作用的研究表明，P. b_B感染对肠道微生物群数量有积极影响，进而刺激了一部分AMPs的表达。然而，AMPs的这种上调并没有导致P. b_B数量的减少。值得注意的是，肠道微生物群并不影响病原体数量，但在P. b_B感染期间促进了宿主存活，这表明其在增加宿主耐受性而非抵抗力方面发挥了作用。
这些发现表明，虽然依赖Imd的AMPs可能不会介导我们系统中的三方相互作用，但微生物群与宿主的相互作用，如微生物群介导的免疫启动和微生物群数量的变化，可以影响感染结果。这些对感染结果的影响几乎肯定会对细菌毒力的进化施加重要的选择压力。
