  A single gene, regulating its own expression via a positive feedback loop,
constitutes a common motif in gene regulatory networks and signalling cascades.
Recent experiments on the development of competence in the bacterial population
\emph{B. subtilis} show that the autoregulatory genetic module by itself can
give rise to two types of cellular states. The states correspond to the low and
high expression states of the master regulator ComK. The high expression state
is attained when the ComK protein level exceeds a threshold value leading to a
full activation of the autostimulatory loop. Stochasticity in gene expression
drives the transitions between the two stable states. In this paper, we explain
the appearance of bimodal protein distributions in \emph{B. subtilis} cell
population in the framework of three possible scenarios. In two of the cases,
bistability provides the basis for binary gene expression. In the third case,
the system is monostable in a deterministic description and stochasticity in
gene expression is solely responsible for the appearance of the two expression
states.
