Kinetics of glucose stimulatory effect on silica deposition and growth of natural populations of Fragilaria crotonensis

SUMMARY Diatoms are known to exploit organic substrates for growth; however, convincing evidence that they can utilize dissolved organic carbon under natural conditions is not available. In 2008–2009, we performed in situ experiments examining the effect of glucose addition on silica deposition kinetics and growth rates of Fragilaria crotonensis in the eutrophic Řimov Reservoir (Czech Republic). Silica deposition kinetics was measured at 4-h intervals over a 24-h incubation with PDMPO [2-(4-pyridyl)-5{[4-dimethylaminoethyl-aminocarbamyl)-methoxy] phenyl}oxazole] fluorescence probe. A significant stimulatory effect of glucose supplemented at the concentration of 10−4 M on Fragilaria silification was observed at 20 and 24 h. Fragilaria growth rates almost doubled upon glucose enrichment compared with the untreated control at 24 h. In addition, we conducted a dose-response experiment testing the glucose additions from 10−8 to 10−3 M in a 24-h incubation. Glucose stimulated both Fragilaria silification and growth at concentrations >10–7 M, which might occasionally occur in a reservoir as a result of accidental contamination of water by organic pollution.