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Roseobacticides: small molecule modulators of an algal-bacterial symbiosis.

Seyedsayamdost MR, Carr G, Kolter R, Clardy J - J. Am. Chem. Soc. (2011)

Bottom Line: A recent study of Phaeobacter gallaeciensis, a member of the large roseobacter clade of α-proteobacteria, and Emiliania huxleyi, a prominent member of the microphytoplankton found in large algal blooms, revealed that an algal senescence signal produced by E. huxleyi elicits the production of novel algaecides, the roseobacticides, from the bacterial symbiont.Structures of the new family members arise from variable substituents at the C3 and C7 positions of the roseobacticide core as the diversifying elements and suggest that the roseobacticides result from modifications and combinations of aromatic amino acids.Together these studies support a model in which algal senescence converts a mutualistic bacterial symbiont into an opportunistic parasite of its hosts.

View Article: PubMed Central - PubMed

Affiliation: Department of Biological Chemistry and Molecular Pharmacology, Harvard Medical School, Boston, Massachusetts 02115, United States.

ABSTRACT
Marine bacteria and microalgae engage in dynamic symbioses mediated by small molecules. A recent study of Phaeobacter gallaeciensis, a member of the large roseobacter clade of α-proteobacteria, and Emiliania huxleyi, a prominent member of the microphytoplankton found in large algal blooms, revealed that an algal senescence signal produced by E. huxleyi elicits the production of novel algaecides, the roseobacticides, from the bacterial symbiont. In this report, the generality of these findings are examined by expanding the number of potential elicitors. This expansion led to the identification of nine new members of the roseobacticide family, rare bacterial troponoids, which provide insights into both their biological roles and their biosynthesis. The qualitative and quantitative changes in the levels of roseobacticides induced by the additional elicitors and the elicitors' varied efficiencies support the concept of host-targeted roseobacticide production. Structures of the new family members arise from variable substituents at the C3 and C7 positions of the roseobacticide core as the diversifying elements and suggest that the roseobacticides result from modifications and combinations of aromatic amino acids. Together these studies support a model in which algal senescence converts a mutualistic bacterial symbiont into an opportunistic parasite of its hosts.

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Major [M + H]+ MS/MS fragments obtained with 13–15.
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fig5: Major [M + H]+ MS/MS fragments obtained with 13–15.

Mentions: HR-ESI-MS analysis of roseobacticides D, E, and F indicated that they contain an additional sulfur atom relative to roseobacticides A, B, and C, respectively (Supporting Information Table S1). On the basis of the 13C chemical shifts of the methyl groups in 13–15, (22–23 ppm, Supporting Information Figures S3–S5, Tables S4–S6) compared to that of the methyl groups in 1, 2, and 12 (∼15 ppm, Supporting Information Table S3 and ref (2)), we suspected that the former contained a methyl persulfide rather than a thiomethyl group at C7. Incubation of 14 with the reducing agent dithiothreitol (DTT) followed by low-resolution HPLC-MS analysis gave a fragment consistent with loss of methanethiol (Supporting Information Figure S6 and Scheme 1, 21, [M + H]+ calcd 255.1, exp 255.1) in agreement with a methyl persulfide functionality. In addition, HR-MS/MS analysis with 14 (Figure 5) gave fragments resulting from the loss of a methyl group ([M + H]+ calcd 286.0117, exp 286.0163), loss of a thiomethyl group (M + H]+ calcd 254.0396, exp 254.0436) and loss of a methyl persulfide ([M + H]+ calcd 222.0675, exp 222.0699) establishing the structure of 14 as shown in Figure 4. The corresponding fragments were also obtained with 13 and 15 (Figure 5 and Supporting Information Table S2). The NOESY spectra of 13–15 did not reveal a cross peak between the methyl protons and the C6-proton (Supporting Information Figure S7), in agreement with the increased distance in a methyl persulfide substituent, and with the assigned structures.


Roseobacticides: small molecule modulators of an algal-bacterial symbiosis.

Seyedsayamdost MR, Carr G, Kolter R, Clardy J - J. Am. Chem. Soc. (2011)

Major [M + H]+ MS/MS fragments obtained with 13–15.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC3211371&req=5

fig5: Major [M + H]+ MS/MS fragments obtained with 13–15.
Mentions: HR-ESI-MS analysis of roseobacticides D, E, and F indicated that they contain an additional sulfur atom relative to roseobacticides A, B, and C, respectively (Supporting Information Table S1). On the basis of the 13C chemical shifts of the methyl groups in 13–15, (22–23 ppm, Supporting Information Figures S3–S5, Tables S4–S6) compared to that of the methyl groups in 1, 2, and 12 (∼15 ppm, Supporting Information Table S3 and ref (2)), we suspected that the former contained a methyl persulfide rather than a thiomethyl group at C7. Incubation of 14 with the reducing agent dithiothreitol (DTT) followed by low-resolution HPLC-MS analysis gave a fragment consistent with loss of methanethiol (Supporting Information Figure S6 and Scheme 1, 21, [M + H]+ calcd 255.1, exp 255.1) in agreement with a methyl persulfide functionality. In addition, HR-MS/MS analysis with 14 (Figure 5) gave fragments resulting from the loss of a methyl group ([M + H]+ calcd 286.0117, exp 286.0163), loss of a thiomethyl group (M + H]+ calcd 254.0396, exp 254.0436) and loss of a methyl persulfide ([M + H]+ calcd 222.0675, exp 222.0699) establishing the structure of 14 as shown in Figure 4. The corresponding fragments were also obtained with 13 and 15 (Figure 5 and Supporting Information Table S2). The NOESY spectra of 13–15 did not reveal a cross peak between the methyl protons and the C6-proton (Supporting Information Figure S7), in agreement with the increased distance in a methyl persulfide substituent, and with the assigned structures.

Bottom Line: A recent study of Phaeobacter gallaeciensis, a member of the large roseobacter clade of α-proteobacteria, and Emiliania huxleyi, a prominent member of the microphytoplankton found in large algal blooms, revealed that an algal senescence signal produced by E. huxleyi elicits the production of novel algaecides, the roseobacticides, from the bacterial symbiont.Structures of the new family members arise from variable substituents at the C3 and C7 positions of the roseobacticide core as the diversifying elements and suggest that the roseobacticides result from modifications and combinations of aromatic amino acids.Together these studies support a model in which algal senescence converts a mutualistic bacterial symbiont into an opportunistic parasite of its hosts.

View Article: PubMed Central - PubMed

Affiliation: Department of Biological Chemistry and Molecular Pharmacology, Harvard Medical School, Boston, Massachusetts 02115, United States.

ABSTRACT
Marine bacteria and microalgae engage in dynamic symbioses mediated by small molecules. A recent study of Phaeobacter gallaeciensis, a member of the large roseobacter clade of α-proteobacteria, and Emiliania huxleyi, a prominent member of the microphytoplankton found in large algal blooms, revealed that an algal senescence signal produced by E. huxleyi elicits the production of novel algaecides, the roseobacticides, from the bacterial symbiont. In this report, the generality of these findings are examined by expanding the number of potential elicitors. This expansion led to the identification of nine new members of the roseobacticide family, rare bacterial troponoids, which provide insights into both their biological roles and their biosynthesis. The qualitative and quantitative changes in the levels of roseobacticides induced by the additional elicitors and the elicitors' varied efficiencies support the concept of host-targeted roseobacticide production. Structures of the new family members arise from variable substituents at the C3 and C7 positions of the roseobacticide core as the diversifying elements and suggest that the roseobacticides result from modifications and combinations of aromatic amino acids. Together these studies support a model in which algal senescence converts a mutualistic bacterial symbiont into an opportunistic parasite of its hosts.

Show MeSH