Host immunological control of the gut microbiota during pupation

免疫效应器最好的研究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，它们在调节宿主-微生物相互作用方面也发挥着重要作用。我们将研究免疫效应器如何在变态过程中改变免疫效应器的用途，以调节肠道微生物区系，而不会通过选择细菌耐药性来损害其作为规范免疫防御的效用。我们将使用蜡蛾Galleria mellonella，它具有良好的免疫基因库，是我们建立的变态肠道免疫模型的基础。具体地说，我们将使用RNAi敲除来操纵在变态肠道中表达的免疫效应器的数量，以便(I)量化细菌耐药性向多达4个免疫效应器组合的进化速度，(Ii)确定细菌耐药性的潜在机制并量化它们对耐药性、交叉耐药性和侧枝敏感性的影响，(Iii)量化在体外和体内以及在存在和不存在肠道微生物区系的情况下耐药性进化的适应成本。因此，我们将测试这一假设，即变态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，以最大限度地减少在肠道微生物区系存在时出现耐药性的可能性。结果将显示宿主如何能够更换和循环中肠，同时控制驻留的微生物区系，这是完全变态进化带来的挑战，因此所有全变态昆虫都面临着挑战。

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.