The European leafhopper, Macrosteles quadripunctulatus, is an important vector of plant diseases in Europe. Leafhoppers feed on plant phloem (sap) that has an overabundance of sucrose but is missing essential nutrients including amino acids. To fill this gap in their diet, leafhoppers host microbial symbionts capable of supplying missing nutrients.
Macrosteles quadripunctulatus has two obligate symbionts, Sulcia muelleri and Nasuia deltocephalinicola. Advances in DNA sequencing allow insect biologists to determine which genes symbionts have and which they lack. This provides important information on what products the symbionts could provide the insects as well as what the insect must provide the symbionts. Living inside an insect provides symbionts with a stable environment and a consistent supply of nutrients. Symbionts often lose genes involved in the production of nutrients supplied by the insect, but keep those that are necessary to maintain the host.
The Nasuia deltocephalinicola genome is the smallest bacterial genome sequenced to date*. This symbiont retains the genes needed to synthesize 2 of 10 essential amino acids. Sulcia muelleri is capable of synthesizing the other eight. Together the symbionts can provide all the essential amino acids. The leafhopper ingests excess sucrose and secretes some of it as waste. The leafhopper has excess capacity for producing ATP, an energy molecule used in metabolic reactions. Interestingly, Nasuia deltocephalinicola has lost the ability to make ATP and derives its ATP or the enzymes needed to make ATP from the leafhopper.
*Bennett GM, Moran NA. 2013. Small, smaller, smallest: the origins and evolution of ancient dual symbioses in a phloem-feeding insect. Genome Biol Evol 5:1675–1688.