Enhanced cellular polyamine pools induced by different nitrogen substrates modify silicification of diatom Paralia sulcata.

Diatoms are important primary producers in aquatic environments, owing to their siliceous frustules that support their biological dominance. Alongside other biomolecules, long-chain polyamines (LCPAs) are considered to be key regulators of silica precipitation in the formation of frustules. However, it remains unclear whether essential polyamines (putrescine, spermidine and spermine), which are derived from nitrogen metabolism in the cellular urea cycle and are required for LCPA synthesis, can influence silicification. Based on a series of culture experiments involving the diatom Paralia sulcata (Ehrenberg) Cleve, 1873, we examine the impact of nitrogen metabolism on silicification by introducing nitrate, ammonium, putrescine, spermidine and spermine. Compared with the frustules from cells cultured with inorganic nitrogen, those cultured with three polyamines exhibit a looser structure and a lower Si:C ratio. Higher levels of cellular polyamines, together with increased levels of amino acids related to the urea cycle (e.g., aspartate and arginine), coincide with pronounced frustule remodelling. These patterns are consistent with uptake of supplied polyamine, rather than generalised endogenous biosynthetic activation. While further substantiation of metabolic reorganisation is required, our findings support a role for intracellular polyamine metabolism in modulating silicification. This discovery sheds significant light on the nitrogen-silicon coupling process in aquatic environments.