A Phenomenological Description of BslA Assemblies Across Multiple Length Scales

Intrinsically interfacially active proteins have garnered considerable interest recently due to their potential use in a range of materials applications. Notably, the fungal hydrophobins are known to form robust and well organized surface layers with high mechanical strength. Recently it was shown that the bacterial biofilm protein BslA also forms highly elastic surface layers at interfaces. Here we describe several self-assembled structures formed by BslA, both at interfaces and in bulk solution, over a range of length scales spanning from nanometers to millimeters. First, we observe transiently stable and highly elongated air bubbles formed in agitated BslA samples. We study their behavior in a range of solution conditions and hypothesize that their dissipation is a consequence of the slow adsorption kinetics of BslA to an air/water interface. Second, we describe elongated tubules formed by BslA interfacial films when shear stresses are applied in both a Langmuir trough and rheometer. These structures bear a striking resemblance, although much larger in scale, to the elongated air bubbles formed during agitation. Taken together, this knowledge will better inform the conditions and applications of how BslA can be utilized in the stabilization of multiphase materials.