Abstract :
[en] Background: Aphids are known to live in symbiosis with specific bacteria, called endosymbionts which can be
classified as obligate or accessory. Buchnera aphidicola is generally the only obligatory symbiont present in aphids,
supplying essential nutrients that are missing in the plants phloem to its host. Pentalonia nigronervosa is the main
vector of the banana bunchy top virus, one of the most damageable viruses in banana. This aphid is carrying two
symbionts: B. aphidicola (BPn) and Wolbachia sp. (wPn). The high occurrence of Wolbachia in the banana aphid
raises questions about the role it plays in this insect. The goal of this study was to go further in the understanding
of the role played by the two symbionts in P. nigronervosa. To do so, microinjection tests were made to see the
effect of wPn elimination on the host, and then, high-throughput sequencing of the haemolymph was used to
analyze the gene content of the symbionts.
Results: We observed that the elimination of wPn systematically led to the death of aphids, suggesting that the
bacterium could play a mutualistic role. In addition, we identify and annotate 587 and 250 genes for wPn and
BPn, respectively, through high-throughput sequencing. Analysis of these genes suggests that the two bacteria
are working together for the production of several essential nutrients. The most striking cases are for lysin and
riboflavin which are usually provided by B. aphidicola alone to the host. In the banana aphid, the genes involved in
the production pathways of these metabolites are shared between the two bacteria making them both essential
for the survival of the aphid host.
Conclusions: Our results suggest that a co-obligatory symbiosis between B. aphidicola and Wolbachia occurs in the
banana aphid, the two bacteria acting together to supply essential nutrients to the host. This is, to our knowledge,
the first time Wolbachia is reported to play an essential role in aphids.
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