Figure 4.

Competitive fitness of S. marcescens with coral commensals. Coral commensal strains shown to inhibit β-𝒟-galactopyranosidase activity in S. marcescens PDL100 were grown in coculture on high-molecular-weight fraction of A. palmata mucus with wild-type PDL100 and transposon mutant CK2A4. To prepare inoculum of S. marcescens strains, overnight cultures were serially diluted and wild type and CK2A4 were mixed in 1:1 ratio and inoculated at 10² cfu ml⁻¹. The coral commensals (Photobacterium sp. 33G2, P. damselae 33G4, Exiguobacterium sp. 33G8, P. leiognathi 33C4, P. leiognathi 33E3 and Vibrio harveyi 34B3) were grown separately, mixed as a cocktail and inoculated at 10⁴ cfu ml⁻¹ concurrently with S. marcescens. (a) In monocultures (black lines) of S. marcescens without coral commensals, the wild type (filled square) and CK2A4 mutant (empty square) reached the same population densities. In the coculture on high-molecular-weight fraction of A. palmata mucus in the presence of the coral commensals, growth of S. marcescens was significantly reduced (gray line). Averages of three biological replicates (three independent cultures) are shown. Error bars are standard errors. (b) Fitness of the mutant versus the wild type in the presence of the commensals was estimated by patching of Serratia colonies onto media with the appropriate antibiotics. The relative proportion of the wild type is shown as the gray portion of the stacked column.