Fig. 4

Spatial structure of the epiphytic microbial community at the tip of N. luetkeana blades. Bacteria at the tip of kelp blades form a dense biofilm. A and B show whole-mount images of samples collected on different dates; C is a cross section showing the thickness of the surface biofilm relative to the kelp cell surface. Microorganisms are intermixed, always within 10 microns of other taxa, and often directly adjacent to cells of disparate taxa or diatoms (red arrowheads). Granulosicoccus aggregate in clusters while other taxa are more dispersed. Abundant Bacteroidetes filaments appear to be lying across the other taxa in (A) and (B). In the cross section (C), filaments of Bacteroidetes and Gammaproteobacteria project into the water column. D Cross section showing diatoms embedded within the bacterial biofilm