  Non-motile elongated bacteria confined in two-dimensional open micro-channels
can exhibit collective motion and form dense monolayers with nematic order if
the cells proliferate, i.e., grow and divide. Using soft molecular dynamics
simulations of a system of rods interacting through short range mechanical
forces, we study the effects of the cell growth rate, the cell aspect ratio and
of the sliding friction on nematic ordering and on pressure fluctuations in
confined environments. Our results indicate that rods with aspect ratio >3.0
reach quasi-perfect nematic states at low sliding friction. At higher
frictions, the global nematic order parameter shows intermittent fluctuations
due to sudden losses of order and the time intervals between these bursts are
power-law distributed. The pressure transverse to the channel axis can vary
abruptly in time and shows hysteresis due to lateral crowding effects. The
longitudinal pressure field is on average correlated to nematic order, but it
is locally very heterogeneous and its distribution follows an inverse
power-law, in sharp contrast with non-active granular systems. We discuss some
implications of these findings for tissue growth.
