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Teams Sequence Bed Bug Genome

Cimex lectularius

NEW YORK (GenomeWeb) – Two teams reporting in Nature Communications have taken a crack at sequencing and analyzing the genome of the common bed bug, Cimex lectularius.

Together, the studies are offering insights into the blood-sucking arthropod's recent resurgence, providing a look at their potential insecticide resistance mechanisms, recent adaptations, and broader biology.

"[D]espite their static look, we know that they continue to evolve, mostly in ways that make it harder for humans to dissociate with them," George Amato, director of the American Museum of Natural History's Sackler Institute for Comparative Genomics, said in a statement. "This work gives us the genetic basis to explore the bedbug's basic biology and its adaptation to dense human environments."

For the first of the two studies, Amato and colleagues from the AMNH, Weill Cornell Medical College, and elsewhere presented an almost 700 million-base bed bug draft genome assembly using a combination of long- and short-read sequencing methods. Along with bed bug sequences, the reads contained information on C. lectularius-associated microbes, pointing to the presence of at least 400 bacterial species, including the endosymbiont Wolbachia.

The team also produced RNA sequence data for adult male and female bed bugs and C. lectularius representatives at various stages of development — transcriptome data used to help annotate nearly 37,000 coding and non-coding bed bug gene models and to uncover informative gene expression shifts.

When the team tracked gene expression across the bed bug life cycle, for example, it saw certain genes that spring into action when an insect consumes its first blood meal.

By comparing bed bug genes to those found in other insects, the researchers identified sets of genes related to everything from blood feeding to insecticide resistance. A broader phylogenetic analysis based on thousands of orthologous protein sequences placed the bed bug near the Chagas disease-carrying kissing bug Rhodnius prolixus.

Finally, the group searched for city-wide phylogenetic structure in bed bug samples from across New York City using available PathoMap data — metagenomic sequences generated for samples from 465 subway stations and almost 1,000 other sampling sites across the city.

That analysis indicated that "areas of the city in close proximity to each other show bed bug populations that are related to each other," Amato and his co-author wrote, noting that "one borough's population can be distinct from others."

In a second Nature Communications study, members of an international team put together a 650 million-base draft genome sequence housing more than 14,000 predicted protein-coding genes.

Through comparisons with sequences from 45 other arthropod species, they began uncovering new and known contributors to bed bug insecticide resistance, including not only transport- and enzyme-related genes, but also those coding for components of the bed bug cuticle.

"The genome sequence shows genes that encode enzymes and other proteins that the bedbug can use to fight insecticides, whether by degrading them or by preventing them from penetrating its body," co-author Coby Schal, an entomology researcher at North Carolina State University, said in a statement.

That analysis also highlighted genes mediating bed bug interactions with human hosts, bacterial symbionts, and one another. For example, the team detected genes that help explain how female bed bugs reinforce a region in their abdomens to survive a potentially dangerous form of sexual intercourse known as "traumatic" or "hypodermic" insemination, in which males use sickle shaped organs to jab sperm into the female.

The researchers detected a streamlined chemosensory gene repertoire, this time compared to the closely related pea aphid, but a jump in representation by genes coding for proteins that help digest blood and overcome platelet aggregation.

Along with these and other gene family contractions and expansions, Schal and colleagues uncovered 805 genes that they suspect were acquired through lateral gene transfer from bacteria. So far, they have taken a closer look at half a dozen genes from the latter set, which are rife with candidate sequences believed to stem from Arsenophonus and Wolbachia. 

"Because of the presence of Wolbachia bacteria in Cimex, it is possible that some apparent [lateral gene transfers] are due to assembly errors joining Wolbachia and Cimex sequences," authors of that analysis noted. "However, examination of junctions between eukaryotic and prokaryotic sequences spanning sequence reads and cloned paired ends strongly supports that nearly all of these are legitimate [lateral gene transfer events]."