Accumulation of mutants in "aging" bacterial colonies is due to growth under selection, not stress-induced mutagenesis

Several bacterial systems show behavior interpreted as evidence for stress-induced mutagenesis (adaptive mutation), a postulated process by which nongrowing cells temporarily increase their general mutation rate. Theoretical considerations suggest that periodic stress-induced general mutagenesis would not be advantageous in the long term, due to the high cost of deleterious mutations. Alternative explanations have been tested for very few of the systems used as evidence for stress-induced mutation. In one prominent system, mutants resistant to rifampicin (Rif^R; rpoB; RNA polymerase) accumulate in cell populations that “age” on solid medium with little net growth. Mutant accumulation was initially attributed to stress-induced general mutagenesis in nongrowing cells. Evidence is presented that these Rif^R mutants accumulate because they grow faster than parent cells during the aging period. Direct tests revealed no increase in the frequency of other mutant types during the aging period.     

Live birth,cumulative live birth and perinatal outcome following assisted reproductive treatments using donor sperm in single women vs. women in lesbian couples: a prospective controlled cohort study

Journal of Assisted Reproduction and Genetics - Assisted reproductive technology (ART) treatments with donor sperm have been allowed for women in lesbian relationships (WLR) since 2005 in Sweden,...