Abstract
It is important to characterize how medically, industrially, or environmentally important bacteria adhere to surfaces in liquid flows in order to control their cell adhesion and subsequent biofilm formation. Acinetobacter sp. Tol 5 is a remarkably sticky bacterium that autoagglutinates through the adhesive nanofiber protein AtaA, which is applicable to cell immobilization in bioprocesses. In this study, the adhesion and behavior of Tol 5 cells in laminar flows were investigated using flow cell systems. Tol 5 cells autoagglutinated through AtaA and formed cell clumps during flowing. The cell clumps rather than single cells went downward due to gravity and adhered to the bottom surface. Under appropriate shear stress, a twin vortex was caused by a separated flow generated at the rear of the pre-immobilized cell clumps and carried the small cell clumps to this location, resulting in their stacking there. The rearward immobilized cell clumps developed into a large, stable aggregate with a streamlined shape, independent of cell growth. Cell clumps hardly ever developed under weak shear stress that could not generate a twin vortex and were broken up under excessively strong shear stress. These cell behaviors including the importance of clumping are interesting features in the bacterial adhesion processes.
Highlights
Most bacteria initially adhere to surfaces, subsequently make microcolonies, and develop biofilms
To examine the adhesion of Tol 5 resting cells under controlled shear stress conditions, two different flow cell systems equipped with either a round glass tube or a square glass tube as an observation cell were constructed. They had an inner diameter (ID) with a similar radius or dimension as the inlet and outlet tubes and had the same surface material surrounding the analysis area so that flow separation generated at the tube joints and heterogeneous adhesion arising from heterogeneity in surface materials could be theoretically ignored
A constant volume (7 mL) of bacterial cell suspensions of Tol 5 WT and the ΔataA mutant at an optical density at 660 nm (OD660) of 0.2 were flowed through the tubular cell at different velocities (300, 400, 500, and 600 μL min−1), which produced shear stresses of 5.68, 7.57, 9.46, and 11.35 mN m−2, respectively, and bacterial cells that adhered to the inner surface of the tubular cell during the flow were quantified by staining with crystal violet
Summary
Most bacteria initially adhere to surfaces, subsequently make microcolonies, and develop biofilms In many cases, these steps occur and proceed in a liquid flow and are significantly affected by shear stress[1]. Bartonella henselae, Bartonella quintana, and Yersinia enterocolitica, pathogenic bacteria that have trimeric autotransporter adhesin (TAA) for cell adherence, exhibit the adherence that appear more significant under dynamic conditions than static conditions[13]. These bacterial adhesive behaviors in response to shear stress vary among bacterial strains due to the diversity of their cell surface components or appendages. The cell behavior of this sticky bacterial strain in laminar flows and the effect of shear stress on its cell adhesion were investigated
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