The invasive lifestyle of "Wolbachia" in the banana aphid "Pentalonia nigronervosa": Implications for horizontal transmission

Details

Supervisors

Hance, Thierry ; Renoz, François

Faculty

Faculté des sciences

Degree label

Master [120] en biologie des organismes et écologie, à finalité approfondie

Abstract

en"Wolbachia" is an intracellular bacterium widely known for its wide host range among arthropods and for its ability to manipulate host reproduction. The remarkable manipulative capacity of this bacterium has led to its integration into many biological pest control programmes. The symbiont seems to defy all attempts at categorisation, presenting highly variable impacts depending on the host species, within the mutualism-parasitism spectrum. Despite its invasive nature and its capacity for reproductive manipulation, the host-"Wolbachia" relationship may only be facultative in some cases and may have evolved into an obligatory mutualistic relationship in others. We also know that "Wolbachia" must have a strong capacity for horizontal transmission to explain such a wide distribution, but the underlying mechanisms are still largely unknown. Using fluorescent in situ hybridization (FISH) microscopy, this work described the cellular tropism of "Wolbachia" throughout the embryonic stages of the aphid "Pentalonia nigronervosa". The images reveal the presence of the bacterium at all embryonic stages, in a large part of the digestive tract and in many other somatic tissues such as the antennae, legs and rostrum. A particular mode of vertical transmission has been uncovered, enabling the bacterium to maintain a bacterial pool in the germarium of embryos. This extensive tissue tropism could suggest a highly adaptive and invasive lifestyle for "Wolbachia" in "P. nigronervosa". In addition, "Wolbachia" were detected in all banana tissues in contact with aphids, from leaves to roots. All these elements suggest the potential transfer of the symbiont via the plant sap, providing elements for understanding the mechanisms behind this remarkably wide distribution among phylogenetically distant arthropod species. The combined evidence from confocal imaging and the successive failures of artificial transmission by microinjection of the bacterium in this work appear to be consistent with the most recent studies published on "Wolbachia" supergroup M in aphids, and more specifically the "wPni" strain present in the banana aphid, indicating a close relationship with the host. "Wolbachia" does appear to be involved in an intimate relationship with "P. nigronervosa" and probably offers benefits to the host that merit further investigation in future work.