University of Rochester scientists discovered a bacterial parasite that is capable of inserting almost its entire genome into the genome of the host. This throws another wrench into the evolution debate, as different species are shown to modify the genes of each other, not just within the species due to environmental factors.
How does Wolbachia transfer its genes to other species? When the Wolbachia invades an organism, usually an insect, it eventually reaches the host’s eggs or sperm. Once there, Wolbachia DNA is ensured passage to its host’s offspring. But if the host cells accidentally pick up Wolbachia DNA as they routinely repair their damaged DNA, resulting genetic changes in the host cells may also be passed on to the host’s offspring.
It was the Wolbachia’s known ability to infect its hosts’ reproductive organs together with an earlier discovery by other researchers of a Wolbachia genome incorporated into a beetle genome that initially inspired the research team to screen the genomes of invertebrates for Wolbachia genes. Early in the screening, they found evidence that some Wolbachia genes were fused to the genes of the fly, as if they were part of the same genome.
In an attempt to isolate the fly genes from the Wolbachia genes, the researchers killed all of the Wolbachia in a colony of fruit flies by feeding antibiotics to the flies. Follow-up testing of the fly DNA for Wolbachia DNA revealed, to their dismay, that it still tested positive for Wolbachia DNA. The researchers eventually discovered that they were detecting copies of the parasite’s genome that remained in the fly genome, not the bacteria itself.
The researchers also verified that the Wolbachia genes were inherited like “normal” insect genes in the chromosomes. In addition, they confirmed that some of the genes were “transcribed” in uninfected flies, meaning that they contain copies of the gene sequence that could be used to make Wolbachia proteins.
The discovery of frequent lateral gene transfer has important implications for genome-sequencing projects in which bacterial DNA has typically been discarded as contamination. This study indicates that such discarded bacterial DNA may very well be part of the organism’s genome, and may even carry functioning traits.
The discovery of frequent lateral gene transfer also has important implications for pest and disease control. If, for example, laterally transferred genes become vital to a disease-causing or transmitting host species, the transferred genes could serve as new disease-fighting targets.
In the future, the researchers hope to investigate whether other bacteria besides Wolbachia are engaging in frequent lateral gene transfer.
National Science Foundation Press Release: One Species’ Genome Discovered Inside Another Species’ Genome