Cerataphis brasiliensis yeast-like symbiont genome sequence. Cerataphis brasiliensis yeast-like symbiont

All aphids maintain symbiotic microorganisms that synthesize essential amino acids that are in insufficient quantities in the phloem-sap diet of the aphid. While most aphids harbor the intracellular bacterium Buchnera aphidicola, a lineage of aphids in the family Cerataphidini has lost Buchnera. These aphids have established a symbiosis with a fungus in the family Cordycepitaceae, known as the yeast-like symbiont (YLS). The YLS is closely related to entomopathogenic fungi such as Metarhizium and Cordyceps, and likely evolved from pathogenic ancestors. The genome of the YLS provides a unique opportunity to study the changes that accompany a shift from a pathogenic to a symbiotic relationship with a host. Many symbionts experience extreme population bottlenecks during vertical transmission, and the YLS genome presents a natural test of the effects of small effective population size on a eukaryotic genome.