MALDI-TOF MS analysis of the extracellular polysaccharides released by the diatom Thalassiosira pseudonana under various nutrient conditions

Investigation of the production and structural characteristics of the extracellular polysaccharides (ECPS) released by diatoms according to nutrient status is urgently necessary for our understanding of the roles of ECPS in aquatic ecosystem. In this study, the effects of N and P depletion and variable nutrient sources on the production and structural characterization of the soluble ECPS released by the marine diatom Thalassiosira pseudonana in batch culture were examined. The abundance of the soluble ECPS produced under N (NO₃ ⁻) depletion was higher than that obtained in the P (PO₄ ³⁻) depletion and control treatments. NH₄ ⁺ rather than NO₃ ⁻ and urea and sodium-glycerophosphate rather than PO₄ ³⁻ were found to induce a higher abundance of soluble ECPS production at the end of the experiment, indicating that the abundance of soluble ECPS is also affected by the nutrient source. Matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS) analysis of the structural characteristics of the soluble ECPS samples showed that the degree of polymerization (d.p.) profiles and the distribution of the polymers with different molecular masses varied in response to nutrient depletion and different nutrient sources. An increase in the proportion of both low- and high-molecular-weight polymers under the N (NO₃ ⁻) and P (PO₄ ³⁻) depletion treatments was found. Based on the different characteristics of high- and low-molecular-weight polymers, our results suggest that the production of soluble ECPS may be one of the strategies that T. pseudonana utilizes to survive under nutrient stress conditions.