Effects of potassium iodide on the growth and metabolite accumulation of two planktonic diatoms

In this study the effects of potassium iodide on the growth and metabolite accumulation of Nitzschia closterium (Ehr.) W. Smith and Phaedactylum tricornutum Bolin were investigated to assess its possible application to the mass culture of the two diatoms in open environment, extensive systems. The results indicated that supplementation of potassium iodide at a concentration of 1000 mg L⁻¹ resulted in a reduction of the induction phase in cultures of N. closterium and P. tricornutum and led to an increase in the accumulation of biomass and extracellular polymeric substances. Conversely, the addition of potassium iodide, at all concentrations tested, showed no obvious effect on the fatty acid profiles of the two diatoms, particularly in the content of eicosapentaenoic and decosahexaenoic acid. Potassium iodide was also found to inhibit the growth of Dunaliella salina, Cryptomonas sp. and Chlorella sp. at minimum inhibitory concentrations of 356.8, 475.9 and 696.2 mg L⁻¹, respectively. It also inhibited bacteria, including species isolated from the two diatom cultures, at a minimum concentration of 400 mg L⁻¹. These results suggest that potassium iodide is an effective agent for inhibiting the proliferation of certain flagellate and non-flagellate algae, and bacteria, thus forming a favorable environment for diatoms to proliferate and consequently improving accumulation of biomass and EPS. These properties of potassium iodide provide a possible solution for preventing contamination from flagellate and non-flagellate algae in mass culture of the two diatoms without causing significant changes in their fatty acid composition.