Do bacteria age?

Abstract

Aging, a progressive deterioration of the physical functions necessary for survival and fertility, resulting from deleterious changes, is one of the most fundamental features of Eukaryotes. Bacteria are thought to be examples of organisms that do not age. They divide by binary fission, which is assumed to be a symmetrical division, such that both daughter cells produced from the parent bacterium have the same constituents with no obvious deterioration. The two daughter cells can continue the process apparently indefinitely giving an impression of immortality. But this thinking has come under scanner in recent years. The following new observations argue that bacteria do age: occurrence of morphologically asymmetric cell division; differential cell behavior during the stationary phase of bacterial growth; and asymmetric inheritance of an older pole by one of the daughter cells during cytokinesis. Is there a loss of fitness when a bacterium eventually divides into two daughter cells? Do they initiate ageing to increase fitness under special circumstances? These issues will be the focus of this article which attempts to resolve this controversy based on current evidence.