Diatom Cultivation: Techniques and Challenges in Single-Cell Isolation

by Wanda Afriliani |

During my internship at IRTA, I studied the behavior of Ulva spp. to optimize their growth. Concurrently, I honed my skills in isolating and cultivating diatoms, which I consider fundamental for exploring their broader applications. Single-cell isolation, achieved through a micropipette, is the simplest method but demands extensive practice. The primary challenges involve selecting a healthy single cell without causing damage or introducing contamination before transferring it to the culture petri dish. In cases of high sample density, a dilution technique aids the isolation process.

The primary aim of single-cell isolation is to establish a monoclonal culture, which facilitates thorough investigations into its physiology, metabolism, growth rate, and responses to environmental factors such as nutrient levels, light, temperature, pH, and salinity. Notably, there are differences in the two culture media I used for marine and freshwater diatom species: F/2 for marine and MBL for freshwater. The key disparity lies in the presence of silica in F/2, which is crucial for the frustule production of marine diatoms. Cyclindrotecha closterium exhibited the highest growth rate during observation among other species.

Furthermore, certain microalgae can be harmful as they produce toxins known as phycotoxins. Blooms of these harmful diatoms can result in mortality and impaired reproduction in marine organisms. Consumption of seafood contaminated with these toxins can cause severe gastrointestinal issues in humans. The primary toxic genera among diatoms include the planktonic genus Pseudo-nitzschia and some species of the genus Nitzschia, such as Nitzschia bizertensis and N. navis-varingica (Caruana & Amzil, 2018).

In addition to the use of diatoms in assessing the quality of the aquatic environment, the main application of diatoms in aquaculture lies in their potential as feed for mussels and fish larvae. Various species, such as Chaetoceros spp., Thalassiosira spp., Skeletonema spp., and Nitzhia closterium, are commonly used for this purpose. The consideration of specific diatom species may vary depending on factors such as the nutritional requirements of target species, availability of diatoms, and economic considerations. Additionally, certain diatom species can be used for oral vaccination methods for fish, such as Thalassiosira pseudonana, Skeletonema costatum, and Tetraselmis subcordiformis, for controlling vibriosis disease.