Role of host nutrition in symbiont regulation: impact of dietary nitrogen on proliferation of obligate and facultative bacterial endosymbionts of the pea aphid Acyrthosiphon pisum

Abstract

The impact of host nutrition on symbiont regulation in the pea aphid Acyrthosiphon pisum was investigated. The population density of the obligate symbiont Buchnera aphidicola positively correlated with dietary nitrogen levels. In contrast, the population density of the facultative symbiont Serratia symbiotica increased in aphids reared on low-nitrogen diets, indicating distinct regulatory mechanisms in the same insect host.

FIG. 1.

The impact of total dietary nitrogen on the body weight of fresh aphids reared on chemically defined diets for 7 days. Open bars, clone IS; closed bars, clone AIST^IS; all data represent means ± standard errors (n = 5). ANOVA results: clone, F_(1,32) = 7.8 (0.01 > P > 0.001); diet, F_(3,32) = 175.8 (P < 0.001); interaction, F_(3,32) = 1.4 (P > 0.05).

FIG. 2.

Symbiont infection in early embryos of the clones IS and AIST^IS. (A) A stage 8 embryo of clone IS; (B) a stage 8 embryo of clone AIST^IS; (C) a stage 12 embryo of clone IS; (D) a stage 12 embryo of clone AIST^IS. Green, red, and blue signals indicate B. aphidicola, S. symbiotica, and nuclei of host cells, respectively. Bars, 50 μm. At stage 8, embryos are infected with the symbionts, and at stage 12, a large syncytial cytoplasm harboring the symbionts cellularizes into many bacteriocytes. Developmental staging of A. pisum is according to reference .