Le Clec'h Winka, Dittmer Jessica, Raimond Maryline, Bouchon Didier, Sicard Mathieu
Department of Genetics, Texas Biomedical Research Institute, PO Box 760549, 78245 San Antonio, TX, USA.
CNRS UMR 7267, Laboratoire Ecologie et Biologie des Interactions, Université de Poitiers, 5 rue Albert Turpain, 86073 Poitiers, France.
Proc Biol Sci. 2017 Jul 26;284(1859). doi: 10.1098/rspb.2017.1076.
Vertical transmission mode is predicted to decrease the virulence of symbionts. However, , a widespread vertically transmitted endosymbiont, exhibits both negative and beneficial effects on arthropod fitness. This 'Jekyll and Hyde' behaviour, as well as its ability to live transiently outside host cells and to establish new infections via horizontal transmission, may reflect the capacity of to exhibit various phenotypes depending on the prevailing environmental constraints. To study the ability of to readily cope with new constraints, we forced this endosymbiont to spread only via horizontal transmission. To achieve this, we performed serial horizontal transfers of haemolymph from -infected to naive individuals of the isopod Across passages, we observed phenotypic changes in the symbiotic relationship: (i) The titre increased in both haemolymph and nerve cord but remained stable in ovaries; (ii) infection was benign at the beginning of the experiment, but highly virulent, killing most hosts after only a few passages. Such a phenotypic shift after recurrent horizontal passages demonstrates that can rapidly change its virulence when facing new environmental constraints. We thoroughly discuss the potential mechanism(s) underlying this phenotypic change, which are likely to be crucial for the ongoing radiation of in arthropods.
垂直传播模式预计会降低共生菌的毒力。然而，一种广泛存在的垂直传播内共生菌，对节肢动物的适应性既表现出负面影响，也有有益影响。这种“善恶兼具”的行为，以及它在宿主细胞外短暂生存并通过水平传播建立新感染的能力，可能反映了其根据当前环境限制表现出各种表型的能力。为了研究该共生菌轻松应对新限制的能力，我们迫使这种内共生菌仅通过水平传播扩散。为实现这一点，我们将感染了该共生菌的等足目动物的血淋巴从感染个体连续水平转移到未感染的个体。在多次传代过程中，我们观察到共生关系中的表型变化：（i）该共生菌在血淋巴和神经索中的滴度增加，但在卵巢中保持稳定；（ii）在实验开始时，该共生菌感染是良性的，但毒性很强，仅经过几次传代就杀死了大多数宿主。反复水平传代后的这种表型转变表明，该共生菌在面对新的环境限制时能够迅速改变其毒力。我们深入讨论了这种表型变化背后的潜在机制，这些机制可能对该共生菌在节肢动物中的持续辐射至关重要。
