Inhibition of swarming of S. marcescens PDL100 by coral commensals. Swarming of S. marcescens PDL100 on AB 0.4% swarm agar next to a sterile glass fiber GF/C disk is shown in (a). Individual coral commensal strains (Photobacterium sp. 33G2 (b), P. damselae 33G4 (c), Exiguobacterium sp. 33G8 (d), P. leiognathi 33C4 (e), P. leiognathi 33E3 (f) and Vibrio harveyi 34B3 (g)) were grown in marine broth and 20 μl were spotted onto a glass fiber GF/C disk on solid marine agar and disks were incubated at 30 °C overnight. Filter disks were placed next to PDL100 (5 μl of overnight culture diluted 1:100 and grown for 2 h). Plates were incubated at 30 °C overnight and all strains, except 33G8, inhibited swarming motility in the pathogen. The experiments were repeated three times, data from one representative experiment are shown.