growth rate in Stewart et al. appears to be at least partially attributed to the preferential localization of inclusion bodies near the old cell wall. This localization is thought to be the passive result of the slow diffusion of the large aggregate, and the exclusion of the aggregate by the nucleoid. A similar mechanism of aging has been found to occur in Schizosaccharomyces pombe, which divides via symmetrical binary fission. Mutations in the cells did not show any signs of aging with respect to growth in the symmetrically dividing E.Coli until the cells with deficient repair enzymes and an increased number of mutations caused the growth rate to decrease, the repair-deficient cells reduced growth in a stepwise manner which suggest that single mutations can cause a growth reduction or can cease growth completely which caused the bacteria die. However, the original findings of E. coli aging have been partially refuted by more recent microfluidics-based studies, in which individual E. coli showed a constant growth rate for hundreds of consecutive cell divisions, although the death rate increased in each cell division. This discrepancy may be due to the different culturing methods used in the two studies, i.e., growth on agar pads vs. in a microfluidic device. See also Ageing Biological immortality Senescence References Cell biology