Further simulation on survival of mutants under non-selective condition.

The fate of mutants introduced into a population is an interestlng question in relation to the introduction of genetically modified organisms in environment. When a bacterial mutant is introduced into the gut nora, what could be an outcome? Unless there is any selective pressure, such as by antibiotic intake, mutants will be removed at random. In the human gut, the total population remains constant・ Therefore, One bacteria in two will be removed at random at each cell division. We previously computer-simulated the outcome when one mutant was introduced into bacterialflora ofvarioussizes. lnflora ranging ln Size from 10 to 10,000, the mutants disappeared within a finite length of time, and, counter-intuitively, the time required fb∫ complete elimination was proportional to the flora size (1). We extended the work and examined outcomes obtained with variousmutant/flora ratios at various flora sizes. We used the same program as in the previous report・ W(t)+m(t)-W(0)+m(0)-C [11, where w(t) and m(t) respectively indicate the number offlora and mutant bacteria at tlme (number of cell divisions) t, and C the total number of bacteria in the gut. As halfthe population of bacteria are eliminated at random, W(t+1) 2W(tトwr(t) --・ [2],