The insect-killing bacterium Photorhabdus luminescens has the lowest mutation rate among bacteria

摘要

Mutation is a primary source of genetic variation that is used to power evolution.Many studies,however,have shown that most mutations are deleterious and,as a result,extremely low mutation rates might be benefcial for survival.Using a mutation accumulation experiment,an unbiased method for mutation study,we found an extremely low base-substitution mutation rate of 5.94×10^(-11) per nucleotide site per cell division(95%Poisson confdence intervals:4.65×10^(-11),7.48×10^(-11))and indel mutation rate of 8.25×10^(-12) per site per cell division(95%confdence intervals:3.96×10^(-12),1.52×10^(-11))in the bacterium Photorhabdus luminescens ATCC29999.The mutations are strongly A/T-biased with a mutation bias of 10.28 in the A/T direction.It has been hypothesized that the ability for selection to lower mutation rates is inversely proportional to the efective population size(drift-barrier hypothesis)and we found that the efective population size of this bacterium is signifcantly greater than most other bacteria.This fnding further decreases the lower-bounds of bacterial mutation rates and provides evidence that extreme levels of replication fdelity can evolve within organisms that maintain large efective population sizes.