Mutualisms between cnidarian hosts and dinoflagellate endosymbionts are foundational to coral reef ecosystems. These symbioses are often re-established every generation with high specificity, but gaps remain in our understanding of the cellular mechanisms that control symbiont recognition and uptake dynamics. Here, we tested whether differences in glycan profiles among different symbiont species account for the different rates at which they initially colonize aposymbiotic polyps of the model sea anemone Aiptasia (Exaiptasia pallida). First, we used a lectin array to characterize the glycan profiles of colonizing Symbiodinium minutum (ITS2 type B1) and noncolonizing Symbiodinium pilosum (ITS2 type A2), finding subtle differences in the binding of lectins Euonymus europaeus lectin (EEL) and Urtica dioica agglutinin lectin (UDA) that distinguish between high-mannoside and hybrid-type protein linked glycans. Next, we enzymatically cleaved glycans from the surfaces of S. minutum cultures and followed their recovery using flow cytometry, establishing a 48–72 h glycan turnover rate for this species. Finally, we exposed aposymbiotic host polyps to cultured S. minutum cells masked by EEL or UDA lectins for 48 h, then measured cell densities the following day. We found no effect of glycan masking on symbiont density, providing further support to the hypothesis that glycan-lectin interactions are more important for post-phagocytic persistence of specific symbionts than they are for initial uptake. We also identified several methodological and biological factors that may limit the utility of studying glycan masking in the Aiptasia system.

The genetically encoded, small-molecule chemical diversity of filamentous fungi is still largely unexplored and represents an attractive source for the discovery of new compounds. Here we report the production of new chlorinated bianthrones from coculture of two different developmental stages, or morphs, of a marine alga-derived Aspergillus alliaceus (teleomorph: Petromyces alliaceus) strain. The vegetative stage (asexual morph) can be separated from the morph that switched to sexual development (sclerotial morph); both produce distinct secondary metabolite patterns. Ochratoxin (1) was mainly found in the monoculture of the sclerotial morph, while the anthraquinone pigment nalgiovensin (2) was produced by the asexual morph. Surprisingly, combining cultures from both developmental stages in a coculture experiment changed the metabolite profile drastically. The chlorinated congener nalgiolaxin (3) was abundant, and newly produced bianthrones were found. Allianthrone A (4) and its two diastereomers [allianthrones B (5) and C (6)] were isolated, and the new structures were determined by extensive NMR spectroscopic analysis, supported by optical properties and X-ray crystallography. All metabolites were tested in antibiotic and cytotoxicity assays, and allianthrone A (4) showed weak cytotoxic activity against the HCT-116 colon cancer and SK-Mel-5 melanoma cell lines.

The success of symbioses between cnidarian hosts (e.g. corals and sea anemones) and microalgal symbionts hinges on the molecular interactions that govern the establishment and maintenance of intracellular mutualisms. As a fundamental component of innate immunity, glycan-lectin interactions impact the onset of marine endosymbioses, but our understanding of the effects of cell surface glycome composition on symbiosis establishment remains limited. In this study, we examined the canonical N-glycan biosynthesis pathway in the genome of the dinoflagellate symbiont Breviolum minutum (family Symbiodiniaceae) and found it to be conserved with the exception of the transferase GlcNAc-TII (MGAT2). Using coupled liquid chromatography-mass spectrometry (LC-MS/MS), we characterized the cell surface N-glycan content of B. minutum, providing the first insight into the molecular composition of surface glycans in dinoflagellates. We then used the biosynthesis inhibitors kifunensine and swainsonine to alter the glycan composition of B. minutum. Successful high-mannose enrichment via kifunensine treatment resulted in a significant decrease in colonization of the model sea anemone Aiptasia (Exaiptasia pallida) by B. minutum. Hybrid glycan enrichment via swainsonine treatment, however, could not be confirmed and did not impact colonization. We conclude that functional Golgi processing of N-glycans is critical for maintaining appropriate cell surface glycan composition and for ensuring colonization success by B. minutum.

24The success of symbioses between cnidarian hosts (e.g. corals and sea anemones) and micro-25 algal symbionts hinges on the molecular interactions that govern the establishment and 26 maintenance of intracellular mutualisms. As a fundamental component of innate immunity, 27 glycan-lectin interactions impact the onset of marine endosymbioses, but our understanding of 28 the effects of cell surface glycome composition on symbiosis establishment remains limited. In 29 this study, we examined the canonical N-glycan biosynthesis pathway in the genome of the 30 dinoflagellate symbiont Breviolum minutum (family Symbiodiniaceae) and found it to be 31 conserved with the exception of the transferase GlcNAc-TII (MGAT2). Using coupled liquid 32 chromatography-mass spectrometry (LC-MS/MS), we characterized the cell surface N-glycan 33 content of B. minutum, providing the first insight into the molecular composition of surface 34 glycans in dinoflagellates. We then used the biosynthesis inhibitors kifunensine and swainsonine 35 to alter the glycan composition of B. minutum. Successful high-mannose enrichment via 36 kifunensine treatment resulted in a significant decrease in colonization of the model sea anemone 37 Aiptasia (Exaiptasia pallida) by B. minutum. Hybrid glycan enrichment via swainsonine 38 treatment, however, could not be confirmed and did not impact colonization. We conclude that 39 functional Golgi processing of N-glycans is critical for maintaining appropriate cell surface 40 glycan composition and for ensuring colonization success by B. minutum. 41 42 43 sister phylum to dinoflagellates, has glycans that are recognized during shellfish infection by a 75 host galectin receptor [25]. The prevalent nature of glycan-lectin interactions in parasitic groups 76 that are closely related to dinoflagellates suggests that the glycomes of Symbiodiniaceae may 77 also have evolved to gain access to the host cnidarian environment. 78The strongest evidence supporting glycan-lectin recognition during the onset of 79 Symbiodiniaceae mutualisms comes from experimental manipulations of symbiont cells through 80 enzymatic cleavage of surface glycans. Several species of Symbiodiniaceae have been 81 experimentally de-glycosylated, leading to reduced symbiont uptake by larval, juvenile, and 82 adult aposymbiotic animals [26-29]. Though the effects are not entirely consistent from study to 83 study, the data suggest that N-glycans in particular are an important determinant of how rapidly 84 hosts are colonized by symbionts. It remains uncertain whether disruption in the onset of 85 symbiosis is driven primarily by changes in the overall abundance of N-glycans (i.e. quantity) or 86 by changes in the composition of N-glycans (i.e. complexity), particularly the relative 87 proportions of high-mannose, hybrid, and complex N-glycans. 88 Although recent advances in the field of glycomics have made the direct chemical 89 analysis of carbohydrates feasible, most studies probing the Symbiodiniaceae cell surface have 90 relied on indirect lecti...

No abstract