Conclusions
The archaeon H. volcanii forms biofilms in several experimental
systems that can be visualized in the laboratory
using standard protocols developed for bacterial species.
H. volcanii cells develop into biofilm structures that
exhibit complexity in both cellular morphology and
ECM composition. We have reported several key features
of H. volcanii biofilms: structural development through
microcolony formation and maturation phases, visualization
of ECM, including the identification of putative amyloid
fibrils, an archaeal form of social motility, as well as a
chained-long rod morphotype and gene transfer. With
the implementation of fluorescent proteins for biofilm
visualization and the available genetic system, it is clear
that the study of biofilm formation in H. volcanii is not
only a means for understanding haloarchaeal ecology
and physiology, but also acts as an excellent model for the
molecular biology of archaeal biofilms and multicellularbehaviors. Future studies may focus on the genetic identification
of many possible differentiated cell types and the
visualization of their positions in time and space using
fluorescent protein reporters. The likely many genetic
determinants of ECM components, social motility and
the enigmatic mating mechanism for gene transfer in
H. volcanii all remain to be discovered