<p></p><p>Biofilms are used in environmental biotechnologies including waste
treatment and environmentally friendly chemical production. Understanding the mechanisms of biofilm formation
is essential to control microbial behavior and improve environmental biotechnologies. <i>Acinetobacter </i>sp. Tol 5 autoagglutinate through the interaction of the long,
peritrichate nanofiber protein AtaA,
a trimeric autotransporter adhesin. Using AtaA, without cell growth or the
production of extracellular polymeric substances, Tol 5 cells quickly form an unconventional
biofilm. In this study, we investigated the formation process of this unconventional
biofilm, which started with cell–cell interactions, proceeded to cell clumping, and led to the formation of large cell aggregates. The
cell–cell interaction was described by DLVO theory based on a new concept, which considers two independent
interactions between two cell bodies and between two AtaA fiber tips forming a virtual
discontinuous surface. If cell bodies cannot collide owing to an energy barrier
at low ionic strengths but approach within the interactive distance of AtaA
fibers, cells can agglutinate through their contact. Cell clumping proceeds
following the cluster–cluster aggregation model, and an unconventional biofilm containing
void spaces and a fractal nature develops. Understanding
its formation process would extend the utilization of various types of
biofilms, enhancing environmental biotechnologies.</p><p></p>
