Linking bacterial tetrabromopyrrole biosynthesis to coral metamorphosis

An important factor dictating coral fitness is the quality of bacteria associated with corals and coral reefs. One way that bacteria benefit corals is by stimulating the larval to juvenile life cycle transition of settlement and metamorphosis. Tetrabromopyrrole (TBP) is a small molecule produced by bacteria that stimulates metamorphosis in a range of coral species. A standing debate remains, however, about whether TBP biosynthesis from livePseudoalteromonasbacteria is the primary stimulant of coral metamorphosis. In this study, we create aPseudoalteromonassp. PS5 mutant lacking the TBP brominase gene,bmp2. Using this mutant, we confirm that thebmp2gene is critical for TBP biosynthesis inPseudoalteromonassp. PS5. Mutation of this gene ablates the bacterium’s ability in live cultures to stimulate the metamorphosis of the stony coralPorites astreoides. We further demonstrate that expression of TBP biosynthesis genes is strongest in stationary and biofilm modes of growth, wherePseudoalteromonassp. PS5 might exist within surface-attached biofilms on the sea floor. Finally, we create a modular transposon plasmid for genomic integration and fluorescent labeling ofPseudoalteromonassp. PS5 cells. Our results functionally link a TBP biosynthesis gene from live bacteria to a morphogenic effect in corals. The genetic techniques established here provide new tools to explore coral-bacteria interactions and could help to inform future decisions about utilizing marine bacteria or their products for restoring degraded coral reefs.