Morphological and physiological characteristics of domestic freshwater diatom Aulacoseira ambigua

Abstract

Diatoms are eukaryotic algae found in a wide variety of aquatic and terrestrial habitats and play an important role in global primary production. These photosynthetic organisms have a high lipid content and a wide range of photosynthetic pigments. Diatoms take up silicon (Si) and form special silica cell walls called frustules. Freshwater diatoms have unique physiological characteristics adapted to low salinity conditions, but most research on diatoms has focused on marine species. This study focused on the freshwater chain diatom Aulacoseira ambigua, a prominent species in domestic rivers and lakes in the Republic of Korea. Phylogenetic analysis provided insights into the evolutionary relationships of A. ambigua, while morphological analysis using light and electron microscopy proposed a distinct post-cell division process specific to this chain diatom. The growth of A. ambigua was studied under different conditions, with particular emphasis on the concentration of silica (Si), an essential element for diatom growth. The results showed that the Si concentration significantly influenced the growth of A. ambigua. Compared to the conventional growth medium, a high Si concentration resulted in an 81% increase in cell growth, as measured by absorbance at 720 nm. In addition, biomass, fucoxanthin concentration and Fv/Fm (a measure of photosynthetic efficiency) showed significant increases of 113%, 15% and 24%, respectively, under high-Si conditions (1 mM). In contrast, the morphology of the diatom frustules showed no significant changes in response to Si and sodium chloride (NaCl) concentrations. These results improve our overall understanding of the life cycle of A. ambigua and emphasise the importance of Si availability for its physiological properties and growth response. The study contributes to the broader knowledge of diatom biology and provides valuable insights for future research in the cultivation and biotechnological applications of freshwater diatoms, including A. ambigua.