From Hypothesis to Harmony:A Quantitative Exploration of Horizontal Gene Transfer
By John Wadington
Image courtesy of Dr. Christina Burch (pictured)
source: https://bio.unc.edu/faculty-profile/burch/
Dr. Christina Burch, Associate Chair of Development and professor in the Biology Department at the University of North Carolina at Chapel Hill, focuses her research on the genetics of adaption, often dealing with viral evolution. To that end, Dr. Burch and her team sought to prove the previously disputed rules of a very common biological phenomenon that has affected virtually every organism on the planet.
Horizontal gene transfer (HGT) describes the common process of transferring genetic material between organisms (most often bacteria) through means other than parent to offspring. While the specific biological vehicles of transfer vary, Dr. Burch and her team focused on the varying rates of successful transfers between genes and the underlying causes of such successes or failures. Before Dr. Burch’s paper, the complexity and balance hypotheses have been proposed to explain trends of successful HGT through the lens of protein-protein interactions (PPIs). The complexity hypothesis describes the inverse relationship between increased homological divergence and successful HGT, while the balance hypothesis describes the same kind of relationship between the magnitude of PPIs of a gene and its successful HGT.¹ Dr. Burch and her team investigated the root of these patterns with the intention of not only proving the two hypotheses quantitatively, but also solidifying the interaction between them to show the coupled effects of protein connectivity and genetic divergence on horizontal transferability.
To quantitatively prove these hypotheses, Dr. Burch and her team worked with 74 existing whole genome shotgun libraries which were analyzed using a series of statistical techniques to simultaneously evaluate the hypotheses’ accuracy while controlling for potential sources of error.¹ Despite the challenges of other biological influences on HGT and limited global knowledge on many genes’ transferability, Dr. Burch and her team were successful. They were able to quantitatively prove that HGT decreases with increasing PPIs in addition to showing that homological divergence reduced transferability more for genes with higher magnitudes of PPIs than with lower. With these conclusions, both the balance and complexity hypotheses were shown not only to be true and quantitatively provable, but shown to interact and compound in their effects on HGT.¹
Throughout the experiment, Dr. Burch maintains it was paramount to remain organized in the face of such an overwhelming amount of data.² Furthermore, such expansiveness of the data speaks to the relevance of conclusions made from it. Since HGT plays such an important role in many evolutionary phenomena such as antibiotic and viral resistance, understanding its limitations may prove integral infields beyond genomics such as medicine.² Though, given such broad relevance, both biological and otherwise, the true extent of the applications remains to be seen.
References:
Burch, Christina, et al. Empirical Evidence That Complexity Limits Horizontal Gene Transfer. Genome Biology and Evolution. 15(6).doi:https://doi.org/10.1093/gbe/evad089.5/26/232.
Interview with Christina Burch, Ph.D. 9/18/233.
Burch, Christina-UNC Department of Biology. https://bio.unc.edu/faculty-profile/burch/. 9/28/23