Université Grenoble Alpes, Laboratoire d'Ecologie Alpine LECA UMR5553, F-38000, Grenoble, France.
Centre National de la Recherche Scientifique, Laboratoire d'Ecologie Alpine LECA UMR5553, F-38000, Grenoble, France.
Parasit Vectors. 2018 Mar 2;11(1):121. doi: 10.1186/s13071-018-2741-8.
Insect microbiota is a dynamic microbial community that can actively participate in defense against pathogens. Bacillus thuringiensis (Bt) is a natural entomopathogen widely used as a bioinsecticide for pest control. Although Bt's mode of action has been extensively studied, whether the presence of microbiota is mandatory for Bt to effectively kill the insect is still under debate. An association between a higher tolerance and a modified microbiota was already evidenced but a critical point remained to be solved: is the modified microbiota a cause or a consequence of a higher tolerance to Bt?
In this study we focused on the mosquito species Aedes aegypti, as no work has been performed on Diptera on this topic to date, and on B. thuringiensis israelensis (Bti), which is used worldwide for mosquito control. To avoid using antibiotics to cure bacterial microbiota, mosquito larvae were exposed to an hourly increasing dose of Bti during 25 hours to separate the most susceptible larvae dying quickly from more tolerant individuals, with longer survival.
Denaturing gradient gel electrophoresis (DGGE) fingerprinting revealed that mosquito larval bacterial microbiota was strongly affected by Bti infection after only a few hours of exposure. Bacterial microbiota from the most tolerant larvae showed the lowest diversity but the highest inter-individual differences. The proportion of Bti in the host tissue was reduced in the most tolerant larvae as compared to the most susceptible ones, suggesting an active control of Bti infection by the host.
Here we show that a modified microbiota is associated with a higher tolerance of mosquitoes to Bti, but that it is rather a consequence of Bti infection than the cause of the higher tolerance. This study paves the way to future investigations aiming at unraveling the role of host immunity, inter-species bacterial competition and kinetics of host colonization by Bti that could be at the basis of the phenotype observed in this study.
昆虫微生物群是一个动态的微生物群落，可以积极参与防御病原体。苏云金芽孢杆菌（Bt）是一种广泛用于防治害虫的天然昆虫病原微生物，作为生物杀虫剂。尽管 Bt 的作用模式已经得到了广泛的研究，但微生物群的存在是否是 Bt 有效杀死昆虫的必要条件仍存在争议。已经有证据表明，更高的耐受性与微生物群的改变之间存在关联，但仍有一个关键点需要解决：改变的微生物群是对 Bt 更高耐受性的原因还是结果？
在这项研究中，我们专注于蚊子物种埃及伊蚊，因为迄今为止在双翅目昆虫上没有关于这个主题的工作，以及苏云金芽孢杆菌以色列亚种（Bti），它被全世界用于蚊子控制。为了避免使用抗生素来治愈细菌微生物群，蚊子幼虫在 25 小时内每小时暴露于逐渐增加的 Bti 剂量下，以分离出最易受感染的幼虫，这些幼虫很快死亡，而更耐受的个体则存活时间更长。
变性梯度凝胶电泳（DGGE）指纹图谱显示，蚊子幼虫的细菌微生物群在暴露于 Bti 仅几个小时后就受到强烈影响。最耐受幼虫的细菌微生物群多样性最低，但个体间差异最大。与最易感幼虫相比，最耐受幼虫体内的 Bti 比例降低，这表明宿主对 Bti 感染有积极的控制作用。
我们在这里表明，改变的微生物群与蚊子对 Bti 的更高耐受性相关，但它是 Bti 感染的结果，而不是更高耐受性的原因。这项研究为未来的研究铺平了道路，旨在揭示宿主免疫、物种间细菌竞争和 Bti 宿主定殖动力学的作用，这些可能是本研究中观察到的表型的基础。
