Mason Charles J, Peiffer Michelle, Felton Gary W, Hoover Kelli
501 ASI Building Department of Entomology, The Pennsylvania State University, University Park, PA 16823, USA.
501 ASI Building Department of Entomology, The Pennsylvania State University, University Park, PA 16823, USA.
J Invertebr Pathol. 2022 Oct;194:107818. doi: 10.1016/j.jip.2022.107818. Epub 2022 Aug 13.
Insect guts often harbor an abundance of bacteria. Many of these members are commensal, but some may emerge as opportunistic pathogens when the host is under stress. In this study, we evaluated how dietary nutritional concentration mediates a shift from commensal to pathogenic, and if host species influences those interactions. We used the lepidopterans (Noctuidae) fall armyworm (Spodoptera frugiperda), beet armyworm (Spodoptera exigua), and corn earworm (Helicoverpa zea) as hosts and a Serratia strain initially isolated from healthy fall armyworm. Diet concentration was altered by bulk reduction in nutritional content with dilution using cellulose. Our experiments revealed that low nutrient diet increased mortality from Serratia for beet armyworm and corn earworm. However, for fall armyworm, little mortality was observed in any of the diet combinations. Dietary nutrition and oral inoculation with Serratia did not change the expression of two antimicrobial peptides in fall and beet armyworm, suggesting that other mechanisms that mediate mortality were involved. Our results have implications for how pathogens may persist as commensals in the digestive tract of insects. These findings also suggest that diet plays a very important role in the switch from commensal to pathogen. Finally, our data indicate that the host response to changing conditions is critical in determining if a pathogen may overtake its host and that these three lepidopteran species have different responses to opportunistic enteric pathogens.
昆虫肠道中常常含有大量细菌。其中许多成员是共生菌，但有些在宿主处于应激状态时可能会成为机会性致病菌。在本研究中，我们评估了饮食营养浓度如何介导从共生菌到致病菌的转变，以及宿主物种是否会影响这些相互作用。我们以鳞翅目（夜蛾科）的草地贪夜蛾（Spodoptera frugiperda）、甜菜夜蛾（Spodoptera exigua）和棉铃虫（Helicoverpa zea）作为宿主，并使用最初从健康草地贪夜蛾中分离出的一种沙雷氏菌菌株。通过用纤维素稀释来大量减少营养成分，从而改变饮食浓度。我们的实验表明，低营养饮食会增加甜菜夜蛾和棉铃虫因沙雷氏菌感染而导致的死亡率。然而，对于草地贪夜蛾而言，在任何饮食组合中都未观察到明显的死亡情况。饮食营养和沙雷氏菌的口服接种并未改变草地贪夜蛾和甜菜夜蛾中两种抗菌肽的表达，这表明涉及其他介导死亡的机制。我们的研究结果对于病原体如何在昆虫消化道中作为共生菌持续存在具有启示意义。这些发现还表明，饮食在从共生菌向致病菌的转变中起着非常重要的作用。最后，我们的数据表明，宿主对变化条件的反应对于确定病原体是否会战胜其宿主至关重要，并且这三种鳞翅目物种对机会性肠道病原体有不同的反应。
