  It has been recently reported that in presence of low Reynolds number (Re<<1)
transport, preformed bacterial biofilms, several hours after their formation,
may degenerate in form of filamentous structures, known as streamers. In this
letter, we explain that such streamers form as the highly viscous liquid states
of the intrinsically viscoelastic biofilms. Such "viscous liquid" state can be
hypothesized by noting that the time of appearance of the streamers is
substantially larger than the viscoelastic relaxation time scale of the
biofilms, and this appearance is explained by the inability of a viscous liquid
to withstand an external shear. Further, by identifying the post formation
dynamics of the streamers as that of a viscous liquid jet in a surrounding flow
field, we can interpret several unexplained issues associated with the
post-formation dynamics of streamers, such as the clogging of the flow passage
or the exponential time growth of streamer dimensions.
