Figure 1.

(A) In cyanobacteria, growth and chromosome replication are coupled so that the amount of protein produced (thus added cell size) during the replication cycle of one chromosome is invariant regardless of the growth rate. The average cell volume (V) increases linearly with respect to the number (N) of unit volume (V₀) from the basal volume (V_basal), i.e., V = N* V₀ + V_basal. (B) The general growth law states that cell size is the sum of all invariant unit cells, where the unit cell is the average cell size per replication origins at initiation [8]. Both cyanobacteria and E. coli appear to follow this principle, with additional basal volume (V_basal) for cyanobacteria (white space in the illustrated cyanobacteria cell). This basal term may reflect specialized structures associated with the cell poles that do not scale with the number of chromosomes.