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Molecular studies of symbiotic proteobacteria in the black bean aphid (aphis fabae scopoli)
Ort / Verlag
ProQuest Dissertations & Theses
Erscheinungsjahr
2005
Link zum Volltext
Quelle
ProQuest Dissertations & Theses A&I
Beschreibungen/Notizen
Modern techniques of molecular biology were used to study the symbiotic bacteria of the black bean aphid (Aphis fabae) which have proved intractable to conventional microbiological techniques. This study showed that Ap. fabae has a very low titre of culturable bacteria, but PCR and FISH reveal it to be symbiotic with the primary aphid bacteria Buchnera, and the secondary aphid bacteria: R-, S-, T- and U-type. Whilst Buchnera was found to be ubiquitous in natural populations of Ap. Fabae, the frequency of infection by secondary bacteria was variable; linked to aphid host plant and time. Buchnera bacteria were housed in mycetocyte cells in embryonic and maternal tissues, whilst secondary bacteria were mostly restricted to embryonic tissues. All types of Ap. fabae symbiotic bacteria were transmitted vertically, with perfect fidelity under laboratory conditions. It was found that diet could have a significant impact on Ap. fabae microbiology, which in turn had marked effects on aphid performance. When feeding on Lamium purpureum (red dead-nettle), Ap. fabae larval growth and reproductive output were significantly reduced. A screen of labiate-polyphagous aphid interactions revealed that the Ap. fabae-Lamium interaction was not general to the labiate plant family. The negative performance effects of L. purpureum on A. fabae were linked to reductions in the nutritional contribution by Buchnera and significant changes to the populations of symbiotic bacteria. Free amino acid titres revealed that Ap. fabae on L. purpureum bore the characteristic signatures of aposymbiosis; elevated concentrations of non-essential amino acids, coupled with reductions in the percentage contribution of essential amino acids to these pools. L. purpureum resulted in significant elevations of secondary bacterial population sizes, and an uncoupling of Buchnera populations sizes from Ap. fabae mass.