*5.10. Data Availability*

*Synoicum adareanum* microbiome Illumina sequence information and associated metadata are described under NCBI BioProject PRJNA597083 (https://www.ncbi.nlm.nih.gov/bioproject/?term= PRJNA597083), and the *S. adareanum* culture collection 16S rRNA gene sequences were deposited in GenBank under MN960541- MN960556. The bacterioplankton sequence information and associated metadata are described under NCBI BioProject PRJNA602715 (https://www.ncbi.nlm. nih.gov/bioproject/?term=PRJNA602715). Antarctic project metadata [71] and environmental metadata (data set identifiers: *Synoicum\_adareanum*\_microbiome\_part1, *Synoicum\_adareanum*\_microbiome\_part2, *Synoicum\_adareanum*\_microbiome\_part3) are available at: POLA3R (2020)—POLA3R Polar Links to Antarctic, Arctic and Alpine Research. Scientific Committee on Antarctic Research, Antarctic biodiversity portal, (www.biodiversity.aq/pola3r/).

**Supplementary Materials:** The following are available online at http://www.mdpi.com/1660-3397/18/6/298/s1, Table S1: ASV occurrences, sequences, and taxonomic affiliations, Table S2: PERMANOVA estimators of drivers of variability, Table S3: Taxonomic distribution of bacterioplankton ASVs, Table S4: Biosynthetic gene clusters in bacterial genomes related to Core80 SaM genera, Table S5: *Synoicum adareanum* collections and preparations for microbiome cultivation, Table S6: *Synoicum adareanum* collections for palmerolide A and microbiome characterization by V3–V4 rRNA gene tag sequencing, Table S7: Bacterioplankton collections used in v4 rRNA gene tag sequencing. Figure S1: Results of pairwise t-tests of PalA levels determined by mass spectrometry, Figure S2: Maximum likelihood 16S rRNA gene phylogenetic tree, Figure S3: Average pairwise similarity within and between *S. adareanum* microbiome community structures, Figure S4: tmMDS plots representing the microbiome of the 63 *S. adareanum* samples, and Figure S5. PalA niche optimum for *S. adareanum* microbiome ASVs.

**Author Contributions:** This work was the result of a team effort in which the following contributions are recognized: conceptualization, A.E.M., P.S.G.C., and B.J.B. methodology and experimentation, A.E.M., N.E.A., L.B., D.E., M.L.H., S.K., C.S.R. and R.M.Y.; validation, K.W.D., M.L.H., and B.J.B. formal analysis, A.E.M., N.E.A., E.D., D.E., S.K., and C.-C.L.; data curation, M.L.H. and C.-C.L.; writing—original draft preparation, A.E.M., B.J.B., N.E.A., D.E., S.K., and C.-C.L.; writing—review and editing, A.E.M., N.E.A., B.J.B., L.B., P.S.G.C., A.E.K.D., D.E., S.K., C.S.R., and R.M.Y.; supervision, A.E.M., B.J.B., P.S.G.C., K.W.D., A.E.K.D., and C.S.R.; project administration, K.W.D.; funding acquisition, A.E.M., P.S.G.C., and B.J.B. All authors have read and agreed to the published version of the manuscript.

**Funding:** Support for this research was provided in part by the National Institute of Health award (CA205932) to A.E.M., B.J.B., and P.S.G.C., with additional support from National Science Foundation awards (OPP-0442857, ANT-0838776, and PLR-1341339 to B.J.B., ANT-0632389 to A.E.M. and Postdoctoral Research Fellowship award DBI-0532893 to C.S.R.). Support for the sequencing of the bacterioplankton was provided as part of the Joint Genome Institute's Community Sequencing Program (JGI-634 to A.E.M.).

**Acknowledgments:** The assistance of several collaborators and students is also acknowledged including Charles Amsler, Margaret Amsler, Jason Cuce, Bill Dent, Alex Dussaq, Cheryl Gleasner, Alan Maschek, Robert W. Read, Andrew Shilling, Santana Thomas, and the Palmer Station science support staff.

**Conflicts of Interest:** The authors declare no conflict of interest.
