Linking bacterial tetrabromopyrrole biosynthesis to coral metamorphosis
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Abstract
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 with and without attachment in a range of coral species. A standing debate remains, however, about whether TBP biosynthesis from live Pseudoalteromonas bacteria is the primary stimulant of coral metamorphosis. In this study, we create a Pseudoalteromonas sp. PS5 mutant lacking the TBP brominase gene, bmp2. Using this mutant, we confirm that the bmp2 gene is critical for TBP biosynthesis in Pseudoalteromonas sp. PS5. Mutation of this gene ablates the bacterium’s ability in live cultures to stimulate the metamorphosis of the stony coral Porites astreoides. We further demonstrate that expression of TBP biosynthesis genes is strongest in stationary and biofilm modes of growth, where Pseudoalteromonas sp. PS5 might exist within surface-attached biofilms on the sea floor. Finally, we create a modular transposon plasmid for genomic integration and fluorescent labeling of Pseudoalteromonas sp. 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 coral restoration.
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Previous studies suggest that Pseudoalteromonas species may not be present in ecologically relevant concentrations that would stimulate coral metamorphosis
Now that you have made the luciferase promoter constructs, it would be cool to screen for things other than growth phase that might bump up expression! Like maybe a compound library screen?
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We also tested broad-host-range promoters, which displayed at least a 457-fold increase in expression compared to assay background across all tested conditions
Not clear what you mean here - were these promoters that weren't originally from Pseudoalteromonas but placed in front of the NLuc gene? Was this as a control?
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Our results represent the first functional characterization of a gene in a marine bacterium conveying a beneficial effect in corals.
this is a really great example of how development of new genetic tools can help dissect species interactions. excited to see where this work goes next!
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Our results suggest that the expression of TBP biosynthesis genes is strongest when bacteria exist in a slow-growth state when Pseudoalteromonas sp. PS5
Curious what growth phase you think the Pseudoalteromonas is in when the metamorphosis assays are performed in Figure 1D? Do you think TBP biosynthesis genes are maximally expressed in the assay?
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