Scientists find link between mutation rate and size

Chennai: Researchers have found a link between mutation rate—how quickly the DNA sequence changes—and genome size.

An international collaboration, led by the Okinawa Institute of Science and Technology Graduate University (OIST) and the University of Sydney, and including researchers from the University of the Ryukyus, the Tokyo Institute of Technology, and RIKEN, uncover evidence that connects increased rates of mutation to changes in genome size in prokaryotes.

In Current Biology, the researchers reported that prokaryotes with higher mutation rates lose genes at a faster pace, and therefore have smaller genomes.

Professor Tom Bourguignon, co-first author of the study and head of the Evolutionary Genomics Unit at OIST, said, “This was a really surprising result.”

“Currently, the most accepted idea is that population size is the main factor that determines genome size in prokaryotes, particularly in endosymbionts, but our research challenges this view.”

Endosymbionts are organisms that live inside the bodies or cells of other organisms, and typically have much smaller genomes than their free-living counterparts. The Evolutionary Genomics Unit researches an endosymbiont called Blattabacterium, a bacterial species that lives inside cockroaches and termites and provides their hosts with vital nitrogen-containing nutrients. But only a small number of these bacteria are passed on from a mother insect host to a daughter insect host, which keeps their effective population size very low.

Dr Yukihiro Kinjo, co-first author and a postdoctoral scholar from the Evolutionary Genomics Unit, said, “At small population sizes, natural selection is much less effective, and evolution is driven more strongly by chance. Without enough selection pressure to maintain specific genes, mutations can arise that inactive and erode these genes, eventually leading to their total loss from the genome.”

In the study, the scientists collected genome data from a diverse range of prokaryotes, including strains from two endosymbiotic lineages and seven free-living lineages.

 

NT Bureau