<b>Supplementary Datasets</b>

Distribution of KO functional genes across 2,185 rMAGs annotated using DRAM.</p><p><br></p><p dir="ltr">Supplementary Data 7. KEGG modules and functional genes across 28 phyla annotated using METABOLIC.</p><p><br></p><p dir="ltr">Supplementary Data 8. Transcript abundance of genes related to prokaryotic carbon, nitrogen, and sulfur metabolism at the ZB seamount.</p><p><br></p><p dir="ltr">Supplementary Data 9.

Transcript abundance of genes related to prokaryotic organosulfur metabolism and their corresponding taxonomic information.</p><p><br></p><p dir="ltr">Supplementary Data 10. Transcript abundance (TPM) of organosulfur metabolism-related genes across the top 35 microbial genera.</p><p dir="ltr">Supplementary Data 11. Identifiers and taxonomic classification of DddL homologous protein sequences.</p><p><br></p><p dir="ltr">Supplementary Data 12.

Identifiers and taxonomic classification of DmdA homologous protein sequences.</p><p><br></p><p dir="ltr">Supplementary Data 13. Identifiers and taxonomic classification of TauD homologous protein sequences.</p><p><br></p><p dir="ltr">Supplementary Data 14. GC-FPD peak characteristics of DMS produced by recombinant DddL candidates in two independent experiments.</p><p><br></p><p dir="ltr">Supplementary Data 15.

HPLC peak characteristics of 5-MTHF produced by recombinant DmdA candidates in two independent experiments.</p><p><br></p><p dir="ltr">Supplementary Data 16. OD415-based quantification of taurine-dependent sulfite production by recombinant TauD candidates.</p><p><br></p><p dir="ltr">Supplementary Data 17. Transcript abundance of prokaryotic genes and their corresponding taxonomic information.</p><p><br></p><p dir="ltr">Supplementary Data 18.

Fisher’s LSD grouping letters for level-2 and level-3 KEGG functional categories in Alphaproteobacteria and Gammaproteobacteria across four operational niche-width groups.</p><p><br></p><p dir="ltr">Supplementary Data 19. Competitive mapping-derived relative genomic representation of vOTUs and rMAGs across 51 seamount metagenomes.</p><p><br></p><p dir="ltr">Supplementary Data 20. Count- and TPM-weighted summaries of computationally predicted viral lifestyles across seamounts and depth zones.</p><p><br></p><p dir="ltr">Supplementary Data 21.

Virus-host linkages predicted using iPHoP.</p><p><br></p><p dir="ltr">Supplementary Data 22. Viral auxiliary metabolic genes (AMGs) and their transcript abundance in the ZB seamount metatranscriptomes.</p><p><br></p><p dir="ltr">Supplementary Data 23. Host and taxonomic information for viruses encoding TauD.</p><p><br></p><p dir="ltr">Supplementary Data 24.

Summary of predicted active-site motifs in viral TauD homologues.</p><p><br></p><p dir="ltr">Supplementary Data 25. Definitions and non-overlapping category assignments of the 306 shared target KOs used for the seamount-Tara Oceans comparison.</p><p><br></p><p dir="ltr">Supplementary Data 26. Analysis-unit metadata and pathway-level TPM sums and proportions used for the formal seamount-Tara Oceans metabolic comparison.</p><p><br></p><p dir="ltr">Supplementary Data 27.

Overall and depth-resolved summaries of the seamount-Tara Oceans DNA and RNA metabolic comparison.</p><p><br></p><p dir="ltr">Supplementary Data 28. Statistical tests for the seamount-Tara Oceans DNA and RNA metabolic comparison.</p><p><br></p><p dir="ltr">Supplementary Data 29. Sample availability and denominator audit for the seamount-Tara Oceans DNA and RNA metabolic comparison.</p><p><br></p><p dir="ltr">Supplementary Data 30.

Abundances of core functional genes across 51 seamount samples.</p><p dir="ltr">Supplementary Data 31. Top three prokaryotic contributors to the transcript abundance of each core metabolic pathway across sampling sites.</p><p><br></p><p dir="ltr">Supplementary Data 32. Joint RPKM-normalized relative transcriptional composition of prokaryotic phyla and viral classes across ZB seamount metatranscriptomes.</p>