Effects of facultative symbionts and heat stress on the metabolome of pea aphids.

We examined metabolite pools of pea aphids with different facultative symbiont infections, and characterized their effects on aphid metabolism in baseline and heat stress conditions. The bacterial symbiont Serratia symbiotica protects aphid hosts from the detrimental results of heat stress and shields the obligate symbiont Buchnera from effects of heat. We investigated whether broad effects on metabolism might correlate with this protection. Both facultative symbiont infection and heat treatment had large effects on the aphid metabolome. All three pea aphid facultative symbionts had similar effects on aphid metabolism despite their evolutionary diversity. Paradoxically, heat triggers lysis of many S. symbiotica cells and a correlated rapid reduction in S. symbiotica titres within aphid hosts. We conclude that facultative symbionts can have substantial effects on host metabolic pools, and we hypothesize that the protective effects of S. symbiotica may reflect the delivery of protective metabolites to aphid or Buchnera cells, after heat exposure.