A promising strategy to overcome limitations in biological control of insect pests is the combined application of entomopathogenic pseudomonads (EPPs) and nematodes (EPNs) associated with mutualistic bacteria (NABs). Yet, little is known about interspecies interactions such as competition, coexistence, or even cooperation between these entomopathogens when they infect the same insect host. We investigated the dynamics of bacteria-bacteria interactions between the EPP Pseudomonas protegens CHA0 and the NAB Xenorhabdus bovienii SM5 isolated from the EPN Steinernema feltiae RS5. Bacterial populations were assessed over time in experimental systems of increasing complexity. In vitro, SM5 was outcompeted when CHA0 reached a certain cell density, resulting in the collapse of the SM5 population. In contrast, both bacteria were able to coexist upon haemolymph-injection into Galleria mellonella larvae, as found for three further EPP-NAB combinations. Finally, both bacteria were administered by natural infection routes i.e. orally for CHA0 and nematode-vectored for SM5 resulting in the addition of RS5 to the system. This did not alter bacterial coexistence nor did the presence of the EPP affect nematode reproductive success or progeny virulence. CHA0 benefited from RS5, probably by exploiting access routes formed by the nematodes penetrating the larval gut epithelium. Our results indicate that entomopathogenic pseudomonads are able to share an insect host with entomopathogenic nematodes and their mutualistic bacteria without major negative effects on the reproduction of any of the three entomopathogens or the fitness of the nematodes. This suggests that their combination is a promising strategy for biological insect pest control.

中文翻译：

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昆虫病原假单胞菌可以与昆虫病原线虫及其共生细菌共享昆虫宿主

克服害虫生物防治局限性的一个有前途的策略是联合应用昆虫病原性假单胞菌（EPP）和与共生细菌（NAB）相关的线虫（EPN）。然而，人们对这些昆虫病原体感染同一昆虫宿主时的种间相互作用（例如竞争、共存甚至合作）知之甚少。我们研究了 EPP 保护假单胞菌 CHA0 和从 EPN 斯氏线虫 RS5 中分离出的 NAB 牛致病杆菌 SM5 之间的细菌-细菌相互作用动态。随着时间的推移，在日益复杂的实验系统中对细菌种群进行了评估。在体外，当CHA0达到一定的细胞密度时，SM5在竞争中被击败，导致SM5群体崩溃。相比之下，将血淋巴注射到大蜡螟幼虫中后，这两种细菌能够共存，正如在另外三种 EPP-NAB 组合中所发现的那样。最后，两种细菌均通过自然感染途径施用，即CHA0口服，SM5线虫载体，从而将RS5添加到系统中。这不会改变细菌共存，EPP 的存在也不会影响线虫繁殖成功或后代毒力。CHA0 受益于 RS5，可能是通过利用线虫穿透幼虫肠道上皮形成的进入途径。我们的结果表明，昆虫病原假单胞菌能够与昆虫病原线虫及其共生细菌共享昆虫宿主，而不会对三种昆虫病原体中任何一种的繁殖或线虫的适应性产生重大负面影响。这表明它们的组合是生物害虫控制的一种有前途的策略。