Can lateral gene transfer cause disease?

Gene transfer between bacterium and host. Copyright – Tim Vernon/Science Source

Kelly Robinson and Julie Dunning Hotopp share a lab in the University of Maryland School of Medicine in Baltimore, and jointly research the role of bacterial lateral gene transfer in human disease. We’re used to human evolution putting imported viral genes to good use and there are several examples of viral genes performing vital roles in human reproduction, for instance being responsible for the formation of the layer of cells – the syncytiotrophoblast – at the junction between maternal and placental tissue. But what about the negative effects of microbial DNA – and what about bacteria?

Robinson and Dunning make their case by examining the discoveries of fragments of bacterial DNA in cancers. Their lab analyzed genome sequence data from nine different tumor types from Cancer Genome Atlas projects and used bioinformatics tools to identify potential DNA integrations. They found sequences from Acinetobacter species in acute myeloid leukemia (AML) samples and from Pseudomonas species in stomach adenocarcinoma (STAD) samples. They report that Ying Xu at the University of Georgia has also identified LGT events in human tumors. His team looked for evidence of genetic material from Helicobacter pylori bacteria and the Epstein-Barr virus, both of which have been associated with gastric cancer. The researchers identified H. pylori integrations in 36 genes in the gastric samples, with more integrations present in the tumors relative to controls. The duo do explain that a number of researchers are very skeptical of these claims of bacterial genetic incorporation – citing the possibilities of lab contamination – but conclude on a positive note: “Despite skepticism from some corners of the scientific community and the difficulties of studying bacterial DNA integrations, we believe that LGTs are an important form of insertional mutagenesis. Perhaps now that putative bacterial DNA integrations have been identified in cancer, more researchers will look for these mutations in other diseases. A bacterial DNA integration that occurs in a human cell and leads to the expression of a bacterial compound recognized by the human immune system has the potential to trigger autoimmune disease, for example. Further research on the occurrence and consequences of LGT in human cells will likely reveal the phenomenon to be much more common and important than currently appreciated.”

Further proof, if ever it were needed, that no genome is an island. Bacteria and viruses have been exchanging genes with just about every plant and animal species on earth, with abandon, since life began.