Bacterial Communities Associated with Host-Adapted Populations of Pea Aphids Revealed by Deep Sequencing of 16S Ribosomal DNA

Abstract

Associations between microbes and animals are ubiquitous and hosts may benefit from harbouring microbial communities through improved resource exploitation or resistance to environmental stress. The pea aphid, Acyrthosiphon pisum, is the host of heritable bacterial symbionts, including the obligate endosymbiont Buchnera aphidicola and several facultative symbionts. While obligate symbionts supply aphids with key nutrients, facultative symbionts influence their hosts in many ways such as protection against natural enemies, heat tolerance, color change and reproduction alteration. The pea aphid also encompasses multiple plant-specialized biotypes, each adapted to one or a few legume species. Facultative symbiont communities differ strongly between biotypes, although bacterial involvement in plant specialization is uncertain. Here, we analyse the diversity of bacterial communities associated with nine biotypes of the pea aphid complex using amplicon pyrosequencing of 16S rRNA genes. Combined clustering and phylogenetic analyses of 16S sequences allowed identifying 21 bacterial OTUs (Operational Taxonomic Unit). More than 98% of the sequencing reads were assigned to known pea aphid symbionts. The presence of Wolbachia was confirmed in A. pisum while Erwinia and Pantoea, two gut associates, were detected in multiple samples. The diversity of bacterial communities harboured by pea aphid biotypes was very low, ranging from 3 to 11 OTUs across samples. Bacterial communities differed more between than within biotypes but this difference did not correlate with the genetic divergence between biotypes. Altogether, these results confirm that the aphid microbiota is dominated by a few heritable symbionts and that plant specialization is an important structuring factor of bacterial communities associated with the pea aphid complex. However, since we examined the microbiota of aphid samples kept a few generations in controlled conditions, it may be that bacterial diversity was underestimated due to the possible loss of environmental or transient taxa.

Are aphid parasitoids locally adapted to the prevalence of defensive symbionts in their hosts?

“…The symbiont communities thus appear to evolve independently in the different aphid species, even though they tend to comprise the same members. This matches observations from pea aphids, in which multiple reproductively isolated host races differ strongly in the relative frequencies of infection with different facultative endosymbionts [57, 58]. There is increasing evidence that such differences are adaptive [59–61], and it will be interesting to determine the main selective forces shaping these symbiont communities.…”

Assessment of a 16S rRNA amplicon Illumina sequencing procedure for studying the microbiome of a symbiont‐rich aphid genus

“…; Gauthier et al . ). Neither Sodalis nor Erwinia is common in aphids, and these genera may have been overlooked in PCR investigations based on the use of specific primers.…”

“…; Gauthier et al . ). These methods are undoubtedly powerful as they do not rely on prior knowledge about the diversity of the communities investigated.…”

Consequences of coinfection with protective symbionts on the host phenotype and symbiont titres in the pea aphid system

“…These symbionts have been mostly studied in the pea aphid, Acyrthosiphon pisum , a species using legumes as plant hosts. The pea aphid is known to host 8 vertically transmitted facultative symbiont taxa (Simon et al ., ; Russel et al ., ; Gauthier et al ., ): 5 γ‐proteobacteria Hamiltonella defensa , Regiella insecticola , Serratia symbiotica , Rickettsiella viridis and PAXS (Pea Aphid X‐type Symbiont), 2 α‐proteobacteria including members of the genera Rickettsia and Wolbachia (the latter being uncommon in natural populations), and finally Spiroplasma belonging to Mollicutes. Most of these facultative symbionts have various phenotypic effects on their aphid host, such as conferring protection against natural enemies (Oliver et al ., ; Scarborough et al ., ).…”