Growth Kinetics of the Endosymbiont Buchnera aphidicola in the Aphid Schizaphis graminum.

The aphid Schizaphis graminum is dependent on its prokaryotic endosymbiont, Buchnera aphidicola. As a means of determining B. aphidicola numbers during the growth cycle of the aphid we have used the quantitative PCR to measure the number of copies of rrs (the gene coding for 16S rRNA, which is present as one copy in the B. aphidicola genome). In addition we have measured the aphid wet weight and the DNA and protein content. The results indicate an approximately parallel (23- to 31-fold) increase of these properties during the period of aphid growth. A 1-day-old aphid (24 mug [wet weight]) has 0.2 x 10 copies of rrs, while a 9-day-old aphid (497 mug [wet weight]) has 5.6 x 10 copies. The coupling of endosymbiont and aphid growth is consistent with the requirement of the endosymbiont for growth and reproduction of the aphid.