Metatranscriptomics analysis of silicon transporters highlights underappreciated contributors to silica cycling in the Baltic Sea

Abstract

The biotic component of the marine silica cycle strongly influences global biogeochemical cycling. Active uptake of dissolved silicic acid (dSi) occurs via silicon transporters (SITs), first characterized in diatoms but widely distributed in eukaryotes. Studying SITs and SIT‐like ( SIT‐L ) gene transcripts provides insights into the dynamics and evolutionary history of diverse biosilicifiers. Using a 2‐yr metatranscriptomics dataset of Baltic Sea surface microbial communities, we identified SIT/SIT‐L genes associated with 11 eukaryotic classes. Although diatoms were previously assumed to drive the Baltic Sea silica cycle, silicoflagellates dominated SIT/SIT‐L expression over the sampling period. SIT/SIT‐L expression and phylogenetic analyses revealed class‐specific patterns, suggesting a complex evolutionary history in dinoflagellates and pronounced clade dynamics in diatoms. Overall, these unexpectedly complex and dynamic shifts in transcriptional investment in silicon transport revealed underappreciated microbial groups driving the Baltic Sea silica cycle.