Figure 1. Growth of bacteria at different growth rates and during a shift-up between growth rates. (a) Composition of bacteria as a function of growth rate. (b) Synthesis of cell components during a shift-up from minimal medium to faster growth in richer medium.

Figure 2. Cytoplasm synthesis during the division cycle. Both the rate of cytoplasm synthesis and the pattern of accumulation of cytoplasm are exponential during the division cycle.

Figure 3. DNA synthesis during the division cycle. Three different patterns are illustrated for cells growing with 20-, 30- and 60-min doubling times. For each growth rate, the time from initiation to termination of DNA replication (the C period) is 40 min. The time between termination of replication and cell division (the D period) is 20 min. The proposed chromosome patterns at the start and finish of the division cycle are illustrated above the graphs. In addition to the rate of DNA synthesis during the division cycle, the pattern of accumulation of DNA during the division cycle is presented. Accumulation of DNA is composed of periods of linear synthesis. The rates during these periods are proportional to the existing number of growing points. The graph of the rate of synthesis is the differential of the accumulation plot. A representation of the cell size expected for cells at the start of the division cycle is presented below each synthetic pattern. The size of the newborn cells are in the ratio of 1:2:4 in the three cultures illustrated here. The number of new initiations at the start of each division cycle are also in the ratio of 1:2:4.

Figure 4. Cell surface synthesis during the division cycle. Before invagination, the cell grows only by cylinder extension. Each cell is drawn to scale, with the volume of the cells increasing exponentially during the division cycle. The shaded regions of the cell indicate the amount and location of wall growth (whether in pole or side wall) each tenth of a division cycle. The width of the shaded area is drawn to scale. Cell surface growth actually occurs throughout the side wall and not in a narrow contiguous zone. The variable locations of wall growth in this figure have no specific meaning, but are meant to show synthesis occurring all over the side wall during the division cycle. Before invagination the ratio of the rate of surface increase to the rate of volume increase is constant. When pole synthesis starts, at age 0.5 in this example, there is an increase in the ratio of the rate of surface increase to the rate of volume increase. Any volume not accommodated by pole growth is accommodated by cylinder growth. At the start of pole growth, there is a reduction in the rate of surface growth in the cylinder. As the pole continues to grow, there is a decrease in the volume accommodated by the pole, and an increase in the rate of growth in the side wall.