Louse-Endosymbiont Genomics Projects

Introduction:

Many species of insects rely on symbiotic relationships with microorganisms. This includes species that are economically and medically important; for example head lice, termites, carpenter ants, aphids, ambrosia beetles, and kissing bugs. In our lab we focus on symbiosis between bacteria and lice. Lice parasitize humans and other mammals and feed exclusively on their blood. This diet lacks certain vitamins and lice rely on bacterial symbionts to synthesis these vitamins. Without bacterial symbionts, lice would likely not exist. Our research seeks to understand how these symbioses began and are maintained in lice.

Collections:

Florida Museum houses a large collection of parasitic lice. These lice have been sampled from around the world from many mammal species, including humans, primates, elephants, rodents, ungulates, and marine mammals. These collections are maintained in freezers to preserve the genetic material in the lice and their symbionts.

Research:

Genome erosion:

A defining characteristic of bacteria in symbiosis with insects is their very small genomes, which results from a process of gene loss during symbiosis. The lice found on humans, chimpanzees, and gorillas are associated with a unique group of symbiotic bacteria. There is strong evidence that gene loss is ongoing in these symbionts, which makes them an ideal model system to study how symbiosis influences genome evolution. With the support of a National Science Foundation DDI Grant, the Reed lab is currently using high-throughput DNA sequencing and high-performance computing to sequence the genomes of bacterial symbionts of lice that infect humans and chimpanzees. From this research we will determine which genes were lost in symbiosis and when. This work is important to understand how symbiosis rapidly alters bacterial genomes.

The family tree of louse symbionts: Our lab is investigating the evolutionary relationship of louse bacterial symbionts with other more familiar bacteria. Julie Allen used genetic data to reconstruct an evolutionary history of thousands of bacteria including louse symbionts. From this data she found that different louse species posses a different symbiont lineage. This is unique in symbiosis between bacteria and insects were closely related insects are in symbisois with closely related bacteria.

Describing the symbiont genome: The genome is all of the genetic material found in a cell. This material is responsible for the organization of the cell and all metabolic activities. Our lab has embarked on a project to sequence the genomes of louse symbionts from Elephant lice, Fur Seal lice, Chimpanzee lice, Wildebeest lice, and Human Lice. We are comparing these genomes to learn how microbial symbiont genomes evolve. Bacteria that live only in an animal host have similar genomes, suggesting that have been subject to the same evolutionary process. This includes not only beneficial symbionts, but pathogens as well. Unique properties of the louse-bacterial symbiosis make it uniquely suited to study symbiont genome evolution.

The ppan plasmid:

LEG_01.jpgThe sequencing of the human louse symbiont’s genome uncovered a small chromosome that encodes for synthesis of an important vitamin. It could be a highly efficient way for the symbiont to assist its louse host. Perhaps this plasmid makes it easier for a bacterium to function as a symbiont. We are investigating this plasmid in additional louse species to understand it has facilitated louse-bacterial symbiosis.