Onchuru Thomas O, Martinez Adam J, Kaltenpoth Martin
Department for Evolutionary Ecology, Institute of Organismic and Molecular Evolution (iOME), Johannes Gutenberg University, Mainz, Germany.
Mol Ecol. 2018 Jul 4. doi: 10.1111/mec.14788.
The evolutionary and ecological success of many insects is attributed to mutualistic partnerships with bacteria that confer hosts with novel traits including food digestion, nutrient supplementation, detoxification of harmful compounds and defence against natural enemies. Dysdercus fasciatus firebugs (Hemiptera: Pyrrhocoridae), commonly known as cotton stainers, possess a simple but distinctive gut bacterial community including B vitamin-supplementing Coriobacteriaceae symbionts. In addition, their guts are often infested with the intestinal trypanosomatid parasite Leptomonas pyrrhocoris (Kinetoplastida: Trypanosomatidae). In this study, using experimental bioassays and fluorescence in situ hybridization (FISH), we report on the protective role of the D. fasciatus gut bacteria against L. pyrrhocoris. We artificially infected 2nd instars of dysbiotic and symbiotic insects with a parasite culture and measured parasite titres, developmental time and survival rates. Our results show that L. pyrrhocoris infection increases developmental time and slightly modifies the quantitative composition of the gut microbiota. More importantly, we found significantly higher parasite titres and a tendency towards lower survival rates in parasite-infected dysbiotic insects compared to symbiotic controls, indicating that the gut bacteria successfully interfere with the establishment or proliferation of L. pyrrhocoris. The colonization of symbiotic bacteria on the peritrophic matrix along the gut wall, as revealed by FISH, likely acts as a barrier blocking parasite attachment or entry into the hemolymph. Our findings show that in addition to being nutritionally important, D. fasciatus' gut bacteria complement the host's immune system in preventing parasite invasions and that a stable gut microbial community is integral for the host's health.
许多昆虫在进化和生态方面的成功归因于与细菌的互利共生关系，这些细菌赋予宿主新的特性，包括食物消化、营养补充、有害化合物解毒以及抵御天敌。豆蝽（半翅目：红蝽科），俗称棉斑红蝽，拥有一个简单但独特的肠道细菌群落，其中包括补充B族维生素的棒状杆菌科共生菌。此外，它们的肠道经常受到肠道锥虫寄生虫梨形利什曼原虫（动质体目：锥虫科）的侵染。在本研究中，我们通过实验生物测定和荧光原位杂交（FISH），报告了豆蝽肠道细菌对梨形利什曼原虫的保护作用。我们用寄生虫培养物人工感染了共生失调和共生昆虫的二龄幼虫，并测量了寄生虫滴度、发育时间和存活率。我们的结果表明，梨形利什曼原虫感染会延长发育时间，并略微改变肠道微生物群的定量组成。更重要的是，我们发现与共生对照相比，感染寄生虫的共生失调昆虫的寄生虫滴度显著更高，且有存活率降低的趋势，这表明肠道细菌成功地干扰了梨形利什曼原虫的定殖或增殖。FISH显示，共生细菌沿肠壁在围食膜上的定殖可能起到了屏障作用，阻止寄生虫附着或进入血淋巴。我们的研究结果表明，除了在营养方面具有重要意义外，豆蝽的肠道细菌在预防寄生虫入侵方面补充了宿主的免疫系统，并且稳定的肠道微生物群落对宿主的健康至关重要。
