Attachment of the Chromosome to the Cell Poles: the Strategy for the Growth of Bacteria in Two and Three Dimensions

Bacteria such asStaphylococcus, Lampropedia, andSarcinadevelop in characteristic two-or three-dimensional groups of cells. We propose here a model of how bacteria may generate such groupings by an extension of an earlier model for rod-shaped bacteria. No other mechanism for forming two- or three-dimensional structures of groups of cells has been proposed. Our earlier model for division of rod-shaped bacteria into nearly equal-sized daughters assumed that the origin and terminus DNA were attached at a critical time to polar wall sites. While such binding was speculative 20 years ago, it has now been established that the DNA for the origin of replication, at least during some part of the cell cycle is located in the pole for several different bacteria. Evidence is also building showing that the terminus DNA region is sometimes located at a position in the cell that will develop into two new poles. Here, a new extension of the concept that polar sites bind specifically origin and terminus DNA of the chromosome is presented that can explain how division takes place in one and then in another dimension to form two-dimensional tablets of four cells or large planar arrays. A further possible extension to three dimensions to generate octets of cells is proposed.