Colony surfaces of the Rhizoid and Soft morphotypes of F. columnare B067. The cells were grown on a filter paper on top of a Shieh agar plate and were visualised under HR-SEM. Panel A: Biofilm of the Rhizoid morphotype covered with an extracellular layer. Panel C: A closer view of a typical area where the surface layer is thin or missing, and large vesicles are visible (size approximately 1 μm). Panels B and D: Views of the colony/biofilm surface of the Soft morphotype where the fibrous layer found in other morphotypes was not detected. For the surface of the Rough morphotype, see Additional file 1. Notice the abundance of large vesicles in the Soft morphotype. Scale bar in A is 10 μm, in B, 40 μm, and in C and D, 4 μm.