Genomics of bacterial symbionts to determine nutritional roles in plant-sap feeding insects

Michael Lansford, a student at the University of Rochester, worked with Dustin Dial and Dr. Gaelen Burke

Abstract: Adelgids are sap-sucking insects that contain bacterial endosymbionts to help them synthesize essential amino acids. The adelgid life cycle alternates between sexual generations that parasitize spruce as a primary host and asexual generations that parasitize a secondary host plant species. The adelgid family consists of five lineages each with a different secondary host plant: Douglas fir, fir, hemlock, larch, and pine. Each adelgid lineage has a different pair of symbionts, a primary symbiont that was acquired by the adelgid first and a secondary symbiont that was acquired second. Vallotia is a symbiont shared between the Douglas fir lineage, where it is the secondary symbiont, and the larch lineage, where it is the primary symbiont. To determine the nutritional roles of Vallotia in different species, genomic data were searched for genes involved in amino acid synthesis. FastQC was used to evaluate the quality of raw adelgid read data. The Georgia Advanced Computing Research Center (GACRC) cluster was used to assemble and annotate genomes from the raw reads. After running scripts to assemble raw reads into scaffolds, BLAST was used to identify which scaffolds were from symbionts. Symbiont genes were annotated using PROKKA and Geneious Prime and biochemical pathways were reconstructed with help from BioCyc. The results showed that Vallotia is primarily responsible for synthesis of all essential amino acids except cysteine in the Douglas fir lineage species A. cooleyi. Gillettellia, the primary symbiont in the Douglas fir lineage, works together with Vallotia in lysine and aromatic amino acid synthesis. In both larch lineage species, Vallotia is only responsible for the final steps in tryptophan synthesis and depends on the secondary symbiont Profftia in A. lariciatus and probably A. abeitis for most steps in aromatic synthesis. These results suggest that Vallotia was acquired by the Douglas fir lineage to account for the loss of most synthesis genes in Gillettellia and Profftia was acquired by the larch lineage to account for the loss of aromatic synthesis genes in Vallotia.