Our observations are consistent with reports of
“irregular” morphological characteristics (labeled as
“involution forms” or “hyphomicrobium-like” structures)
when H. volcanii DS2 is grown on agar medium, as noted
in the original 1975 characterization [39]. Archaeosortase
(artA) overexpression strains also showed an elongated
rod morphology. The ArtA protein has many downstream
targets effecting cell shape and surface decoration, indicating
that it could be a regulatory component of biofilm formation
and/or related systems [94]. Previous observations
of irregular cell morphologies can now be understood as
being coupled with biofilm formation.