Effects of silica limitation on diatom growth and frustule morphology

Abstract

Diatoms are eukaryotic microalgae that serve as important primary producers in our oceans. The diatoms are unique with a cell wall of silicon dioxide with a small amount of water (SiO2•H2O), like a tiny glass house. This cell wall, called frustule, has a myriad of sieve pores and can vary in morphology and size, making them of interest for example morphological species identification and industrial applications. The aim of this study was to find out when the morphology of the frustule starts to change when the diatom is subjected to silica limitation (i.e. silicic acid), as well as how it affects the diatom growth and photochemical activity. This was tested by using five true replicates that were given all the nutrients and minerals they needed, except for silicic acid, and five control replicates that were given everything they needed including silicic acid. Cell density, growth and photosynthetic activity was measured approximately once every week for five weeks. In addition, the diatoms were cleaned from organic material, so the frustules could be viewed in detail using a light microscope to estimate the proportion of deformed/undeformed frustules every week. The analysis showed that cells exposed to silica limitation had a slower generation time than the control treatment. Furthermore, the photosynthetic activity was significantly higher for the control treatment on all days, except for day 8. There was also a significant difference in the number of deformed frustules between the treatment and the control after only eight days. The results showed that limitation of silica has an impact on all parameters (cell growth, photosynthetic activity, and diatom frustule morphology) already after few generations.