Abstract:
Variability in cell sizes is seen
in isogenic bacterial populations despite of maintenance
of cell size homeostasis. Quantification of cell sizes in a bacterial population can help us
elucidate mechanisms that might disturb the size distribution in the community.
Cell
sizes
have been
quan
tified earlier in
E.coli
and found to
be
depend
ent
on growth
rate
.
This dependence results from
multi
-
fork replication in fast growing
E. coli
.
Here we
quantif
ied
cell size
variation
in a
S. aureus
population
and
its
dependence on
growth
rate
.
We
have
developed and optimized an algorithm to detect spherical and ellipsoid c
ells in
label
-
free
DIC images in ImageJ
. We
assess
the
population
density dependence of c
ell
size variations
in a batch culture
and f
ind
no difference in the noise across different
gro
wth phases.
Perturbing
the cell cycle
either
with
Cephalexin
(
c
ell division inhibitor
)
or
with
Hydroxyurea
(
DNA replication inhibitor
)
results in an
increase in mean cell area of
treated cells as compared to non treated cells
. However
no significant change in the
phenotypic noise
is observed
.
This study sets the stage for a quantitative understanding of cell shape variability due to
non
-
genetic factors, across strains
in a gram positive coccal bacterium,
thus
complementing previous wor
k on gram negative
E. coli
.
It suggests that the observation
of
growth rate dependence on cell size variability could be a conserved mechanism.
