How, then, might morphology contribute to natural selection?
Simply put, bacteria with different shapes present
different physical features to the outside world, and these
features help cells cope with and adapt to external
conditions. Even a 0.01% increase in the growth rate of
E. coli can impart a fitness advantage of 10% compared to
its unaltered competitors [5], so improvements need not
be dramatic to be useful. Consistent with these expectations,
shape contributes a measure of survival value in the
face of three ‘Primary’ selective pressures: (1) nutrient
acquisition, (2) cell division, and (3) predators; and in
optimizing five ‘Secondary’ mechanisms: (4) attachment
to surfaces, (5) passive dispersal, (6) active motility, and (7)
internal or (8) external differentiation [1] (Table 1). The
first three are Primary in that they represent fundamental
conditions that determine whether cells live or die because
cells must grow and multiply and resist being killed. The
last five are Secondary in that they represent a suite of
Cur