Process Description of an Unconventional Biofilm Formation by Bacterial Cells Autoagglutinating Through Sticky, Long, and Peritrichate Nanofibers

Abstract

<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>

Single-Cell Adhesion Force Mapping of a Highly Sticky Bacterium in Liquid

“…However, the current result demonstrated that a single Tol 5 cell itself has the ability to very strongly adhere to a surface through the quick interaction of AtaA with the surface. It is considered that the strong initial attachment capacity of Tol 5 cells using AtaA gives this bacterium the property of forming a strongly attached biofilm without the secretion of EPS, as shown previously [35].…”

“…Recently, we showed that autoagglutination through AtaA significantly contributes to biofilm formation of Tol 5 cells by triggering the formation of the biofilm [35,36].…”

“…Before adhering to a surface, a cell must approach the surface to a position from which AtaA can make contact with it [35]. According to the DLVO theory, during this approaching process, a bacterial cell undergoes both attractive and repulsive forces from a surface, and their summation directly affects cell adhesion.…”

“…According to the DLVO theory, during this approaching process, a bacterial cell undergoes both attractive and repulsive forces from a surface, and their summation directly affects cell adhesion. It has been shown that autoagglutination of Tol 5 cells follows the DLVO theory [35], and it can be considered that the interaction between the cell and the surface also follows this theory. At lower ionic strength, the repulsive force is stronger and both cell adhesion and autoagglutination are hindered [8].…”