Department of Entomology, The University of Georgia, Athens, GA, United States of America.
PLoS Negl Trop Dis. 2018 Jul 6;12(7):e0006638. doi: 10.1371/journal.pntd.0006638. eCollection 2018 Jul.
We recently reported that larval stage Aedes aegypti and several other species of mosquitoes grow when living bacteria are present in the gut but do not grow when living bacteria are absent. We further reported that living bacteria induce a hypoxia signal in the gut, which activates hypoxia-induced transcription factors and other processes larvae require for growth. In this study we assessed whether other types of organisms induce mosquito larvae to grow and asked if the density of non-living microbes or diet larvae are fed obviate the requirement for living organisms prior results indicated are required for growth. Using culture conditions identical to our own prior studies, we determined that inoculation density of living Escherichia coli positively affected growth rates of Ae. aegypti larvae, whereas non-living E. coli had no effect on growth across the same range of inoculation densities. A living yeast, alga, and insect cell line induced axenic Ae. aegypti first instars to grow, and stimulated similar levels of midgut hypoxia, HIF-α stabilization, and neutral lipid accumulation in the fat body as E. coli. However, the same organisms had no effect on larval growth if heat-killed. In addition, no axenic larvae molted when fed two other diets, when fed diets supplemented with heat-killed microbes or lysed and heat-killed microbes. Experiments conducted with An. gambiae yielded similar findings. Taken together, our results indicate that organisms from different prokaryotic and eukaryotic groups induce mosquito larvae to grow, whereas no conditions were identified that stimulated larvae to grow in the absence of living organisms.
我们最近报道，在肠道中有活体细菌存在的情况下，埃及伊蚊和其他几种蚊子的幼虫会生长，但在没有活体细菌的情况下则不会生长。我们还报告说，活体细菌在肠道中诱导缺氧信号，从而激活缺氧诱导转录因子和幼虫生长所需的其他过程。在这项研究中，我们评估了其他类型的生物体是否诱导蚊子幼虫生长，并询问非活体微生物的密度或幼虫所摄食的饮食是否可以避免活体生物体对先前结果的需求，这些结果表明生长是必需的。使用与我们之前的研究相同的培养条件，我们确定活体大肠杆菌的接种密度对埃及伊蚊幼虫的生长速度有积极影响，而在相同的接种密度范围内，非活体大肠杆菌对生长没有影响。活体酵母、藻类和昆虫细胞系诱导无菌埃及伊蚊初孵幼虫生长，并刺激类似水平的中肠缺氧、HIF-α稳定和脂肪体中性脂质积累，与大肠杆菌相似。然而，如果将这些生物体热灭活，则对幼虫生长没有影响。此外，当喂食两种其他饮食、补充热灭活微生物或裂解和热灭活微生物的饮食时，无菌幼虫没有蜕皮。在冈比亚按蚊中进行的实验得出了类似的发现。总之，我们的结果表明，来自不同原核和真核生物群的生物体诱导蚊子幼虫生长，而没有发现任何可以在没有活体生物体的情况下刺激幼虫生长的条件。
