Fed-batch cultivation enhances phosphate sufficiency and maintains high biomass accumulation and silicon utilization...

Although phosphorus is supplied at lower levels than silicon in diatom cultivation, its availability strongly influences diatom growth and silicon utilization during large-scale cultivation, yet the optimal phosphate-supplementation strategy remains unclear. Two phosphorus-feeding strategies, maintenance of phosphorus sufficiency and phosphorus resupply after limitation, were compared with a sustained phosphorus-starvation control during 300 L fed-batch cultivation of Cyclotella cryptica, a diatom commonly used in industrial production, under non-limiting silicate conditions using integrated physiological and transcriptomic analyses. This study demonstrates that maintaining continuous phosphorus sufficiency is more effective than phosphorus resupply after limitation or sustained phosphorus starvation. Compared with the phosphorus-resupply treatment, the continuously phosphorus-sufficient treatment achieved a 27.78% higher final cell density, 20.4% greater dry biomass, and 17.3% greater total silicon consumption, with all three differences being statistically significant (P < 0.01). Transcriptomic analysis further showed that phosphorus resupply was associated with a staged recovery pattern, with transcriptional responses related to biosynthesis and growth occurring earlier than those related to photosynthesis and silicon-associated metabolism. Based on these findings, our results demonstrate that maintaining phosphorus sufficiency can improve biomass accumulation and silicon utilization relative to phosphorus resupply after limitation or sustained phosphorus starvation under the 300-L cultivation conditions tested.