Diversity of bacteria associated with natural aphid populations

Abstract

The bacterial communities of aphids were investigated by terminal restriction fragment length polymorphism and denaturing gradient gel electrophoresis analysis of 16S rRNA gene fragments generated by PCR with general eubacterial primers. By both methods, the gamma-proteobacterium Buchnera was detected in laboratory cultures of six parthenogenetic lines of the pea aphid Acyrthosiphon pisum and one line of the black bean aphid Aphis fabae, and one or more of four previously described bacterial taxa were also detected in all aphid lines except one of A. pisum. These latter bacteria, collectively known as secondary symbionts or accessory bacteria, comprised three taxa of gamma-proteobacteria (R-type [PASS], T-type [PABS], and U-type [PAUS]) and a rickettsia (S-type [PAR]). Complementary analysis of aphids from natural populations of four aphid species (A. pisum [n = 74], Amphorophora rubi [n = 109], Aphis sarothamni [n = 42], and Microlophium carnosum [n = 101]) from a single geographical location revealed Buchnera and up to three taxa of accessory bacteria, but no other bacterial taxa, in each aphid. The prevalence of accessory bacterial taxa varied significantly among aphid species but not with the sampling month (between June and August 2000). These results indicate that the accessory bacterial taxa are distributed across multiple aphid species, although with variable prevalence, and that laboratory culture does not generally result in a shift in the bacterial community in aphids. Both the transmission patterns of the accessory bacteria between individual aphids and their impact on aphid fitness are suggested to influence the prevalence of accessory bacterial taxa in natural aphid populations.

FIG. 1.

Electropherograms of the T-RFs produced by AluI-BseRI (AB) digestion (A, C, E, G, I, and K) and SmaI-ClaI-XbaI (SCX) digestion (B, D, F, H, J, and L) of PCR amplicons from 16S rRNA genes from the reference lines of the pea aphid A. pisum LMB95/28 (A and B), R (C and D), IS (E and F), FH (G and H), and MD (I and J) and aphid 1330 from the natural population of A. pisum (K and L). The T-RFs are shown in black, and the internal standards (50, 75, 100, 139, 150, 160, 200, 250, 300, 340, 350, 400, 450, 490, and 500 bp) are shown in gray.

FIG. 2.

DGGE profiles of 16S rRNA gene fragments amplified by PCR using general primers (P2 and P3) from whole-aphid DNA templates. (a) Aphid reference lines and lines in long-term laboratory culture; (b) Bacterial community in one A. pisum aphid with a novel T-RF profile (sample 590, collected from Cytisus scoparius). Numbers in the lanes relate to bands excised from the gel for sequencing (Table 3).