Role of the Tafi Surface Structures in Biofilm Formation by Halophilic Archaea Haloarcula hispanica

The haloarchaeon Haloarcula hispanica was found to possess a new type of surface structures, tafi, assemblage of which depends on the Tat translocation pathway. The present work experimentally confirmed the role of tafi in cell adhesion. The mutant strain with deletion of the gene of the major tafi structural protein (ΔtafA) exhibited drastically lower capacity for adhesion compared to the parent strain at all tested values of salinity (18–25% NaCl) and pH (6.0–8.0). Deletion of the pibD gene, responsible for the synthesis of archaella and type IV pili, also resulted in suppressed biofilm formation, albeit to a lesser degree. The ΔpibDΔtafA double mutant exhibited the lowest adhesive activity, which may indicate synergistic interaction of two adhesion systems. Our data indicate that tafi are the main factor responsible for initial cell attachment to the surface.