Successful Genome Sequencing May Lead to Improved, Non-Chemical Control of Body Lice

June 21, 2010

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Janet Lathrop 413/545-0444

AMHERST, Mass. – Suffering from itchy bites and epidemic disease spread by the lowly body louse over thousands of years, humans may finally have found a tool for fighting back against this pest and discovering its knack for evading pesticides. University of Massachusetts Amherst pesticide toxicologist John Clark, with colleagues at 28 institutions in the U.S., Europe, Australia and South Korea, this week report that they’ve sequenced the genome of the body louse, Pediculus humanus humanus L, the smallest insect genome known.

This is only the second genome to be sequenced of a very ancient insect family that does not undergo complete metamorphosis, that is, development from egg to caterpillar to pupa to adult, but instead grows by gradual metamorphosis.

Clark, of the UMass Amherst veterinary and animal sciences department, and colleagues provided all the inbred louse specimens used in the sequencing project, along with a substantial number of expressed sequence tags in the EST library used to annotate the genome. He also coordinated annotation of the body louse’s “detoxification genes,” again the smallest number seen in any insect, about 107.6 million base pair for males and 105.4 base pair for females, which are important in determining how lice develop resistance and outwit insecticides and other chemical weapons, a specialty of the Clark lab.

“Necessarily, a project of this complexity is the result of collaboration among several laboratories and many outstanding scientists around the world,” Clark points out. “Everyone had a role to play and brought special skills to bear on the achievement.”

First author Ewen Kirkness coordinated the project at the J. Craig Venter Institute, while University of Illinois entomology professors May Berenbaum and Barry Pittendrigh were also instrumental in its success. Findings are reported in the current issue of Proceedings of the National Academy of Sciences. Overall, the new genetic information should yield valuable insights into louse biology and evolution in an insect that is totally dependent upon humans for survival, Clark says.

Further, Berenbaum comments, “Beyond its importance in the context of human health, the body louse genome is of considerable importance to understanding insect evolution.” This genome provides a baseline for understanding how complete metamorphosis came to evolve, allowing insects to colonize every part of the planet, she adds.

As the researchers explain, body louse ecology is quite simple. The bugs live on clothes and suck human blood. This limited lifestyle means the creature has a small number of genes, most of which are responsible for sensing the environment. For example, compared to other insects, lice have very few genes for light-, taste- and odor-receptors.

Clark adds that the body louse has “the smallest number of detoxification enzymes observed in any insect.” This pared-down list makes it an attractive organism for the study of resistance to insecticides and other types of chemical defense, by providing new molecular targets for developing new compounds to fight these pests.

The work also included sequencing the genome of a microbe that lives inside the louse, Candidatus Riesia pediculicola. Here the researchers found genes that allow the body louse to produce pantothenate or Vitamin B5, which it cannot make on its own.

Body lice spread epidemic diseases such as typhus and relapsing fever via bacteria in the Rickettsia, Borellia and Bartonella families, in people who are in poor health or forced to live in crowded, dirty conditions such as trenches in warfare. The body louse is closely related to the head louse, P. humanus capitis, but unlike the head louse, it can live in clothing and spread bacterial diseases.

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