Host immunological control of the gut microbiota during pupation

对免疫效应器的研究最好是作为微生物感染诱导的防御。然而，除了简单的免疫防御外，它们还在宿主-微生物相互作用的调节中发挥重要作用。我们将研究免疫效应物如何通过选择细菌耐药性而不影响其作为典型免疫防御的效用，从而在变态过程中重新用于调节肠道微生物群。我们将使用蜡蛾mellonella，它具有很好的特征免疫基因库，是我们建立的变态肠道免疫模型的基础。具体来说，我们将使用RNAi敲低来操纵在变质肠道中表达的免疫效应物的数量，以便(i)量化细菌对多达4种免疫效应物组合的耐药性进化速度，（ii）确定细菌耐药性的潜在机制，并量化它们对耐药性、交叉耐药性和附带敏感性的影响，（iii）量化体外和体内耐药性进化的适应成本。以及肠道菌群的存在和缺失。因此，我们将验证这一假设，即变质肠道免疫的复杂性已经进化到利用功能不同的免疫效应器的组合，以最大限度地减少肠道微生物群存在时出现耐药性的可能性。结果将显示寄主如何能够在控制常驻微生物群的同时替换和循环中肠，这是完全变态进化所带来的挑战，因此所有全变态昆虫都面临着这一挑战。

Immune effectors are best studied as defenses induced by microbial infections. However beyond simple immune defense they also play important roles in the regulation of host-microbe interactions. We will investigate how immune effectors can be repurposed for regulation of the gut microbiota during metamorphosis without compromising their utility as canonical immune defences by selecting for bacterial resistance. We will use the wax moth Galleria mellonella, which has a well characterized immune gene repertoire and is the basis of our established model of metamorphic gut immunity. Specifically, we will use RNAi knockdown to manipulate the number of immune effectors expressed in the metamorphic gut in order to (i) quantify the rate of bacterial resistance evolution towards combinations of up to 4 immune effectors, (ii) identify the underlying mechanisms of bacterial resistance and quantify their effects on resistance, cross-resistance, and collateral sensitivity, (iii) quantify the fitness costs of resistance evolution both in vitro and in vivo, and in the presence and absence of the gut microbiota. Thus we will test the hypothesis that the complexity of metamorphic gut immunity has evolved to exploit a combination of functionally distinct immune effectors that minimize the probability of resistance emergence in the presence of the gut microbiota. The results will show how the host is able to replace and recycle the midgut while simultaneously controlling the resident microbiota, a challenge posed by the evolution of complete metamorphosis and thus faced by all holometabolous insects.