A study group found that rather than doubling in size every generation, each cell added the same volume (or mass; the term reflects the measurement technique). Crucially a cell that was small added the same volume as a cell that was large.
Why is this the rule? Although this might seem counter-intuitive, over many generations this rule ensures that cells in a population maintain a constant size. Pinning down the growth rule is important, because it provides clues to the underlying biochemical mechanism that ultimately controls growth. The mechanism is probably essential, or nearly so, and thus good target for new antimicrobials.
Surprisingly little is known about biological size control in general.
How bacteria control their size
Source: Phys org