ON ALTERNATIVES TO SELECTION-INDUCED MUTATION IN THE BGL OPERON OF ESCHERICHIA-COLI

Selection-induced mutations are nonrandom mutations that occur as spec ific and direct responses to environmental challenge. Examples of sele ction-induced mutations have been reported both in bacteria and in yea st. I previously showed (Hall 1988) that excisions of the mobile genet ic element IS150 from within bglF are selection induced and argued tha t they occurred because they were potentially advantageous under the s elective conditions employed. Mittler and Lenski (Mittler and Lenski 1 992) have argued that such excisions are not selection induced but tha t they occur randomly in nondividing cells. Here I provide further evi dence that IS150 excisions are induced by selection and that the excis ions are immediately, rather than only potentially, advantageous to th e cell. I also provide evidence that excisions, which Mittler and Lens ki claim occur randomly in saturated broth cultures, actually occur af ter samples from those cultures are plated onto selective medium.