Physiological and transcriptomic responses of Synechococcus to silicate availability

The discovery of silicon (Si) accumulation in Synechococcus has drawn increasing attention to the physiological and mechanistic basis in marine environments. Although growth rates of Synechococcus are generally insensitive to silicate availability, the influence of silicate on Si accumulation and its regulatory mechanisms remains poorly understood. To investigate the response mechanisms of Synechococcus to silicate availability, we integrated physiological, biochemical, and transcriptomic analyses of a coastal strain and a marine strain.

Cultures were grown under silicate-depleted (<1 μmol·L-1) and silicate-repleted (100 μmol·L-1) conditions. Silicate addition enhanced photosynthetic parameters in Synechococcus sp. XM24, reduced cellular carotenoid content in Synechococcus sp. PCC7002, and increased biogenic silica (BSi) in both strains. Transcriptomics revealed that silicate modulated photosynthesis and oxidative phosphorylation pathways in both strains. Under Si-replete conditions, ribosomal genes and protein synthesis were upregulated in Synechococcus sp. XM24, while membrane transport increased and sphingolipid metabolism decreased in Synechococcus sp. PCC7002.

Collectively, our results reveal that Synechococcus exhibits a previously unrecognized physiological and molecular sensitivity to changes in silicate availability at an environmentally relevant concentration (100 μmol·L-1), with strain-specific acclimation strategies linked to their ecological origins. While these findings provide initial insights into the potential mechanisms underlying silicon accumulation in Synechococcus, the binary experimental design limits conclusions about uptake kinetics, which require validation with a full concentration gradient in future studies. Nonetheless, this study still advances our understanding of the mechanisms underlying silicon accumulation in Synechococcus.