The storage products of diatoms, under nutrient limitation

In the present study, the effect of nutrient limitation on the storage products of diatoms will be assessed. The major storage products for diatoms are carbohydrates and lipids. Diatoms increase their total lipid content under nitrate, phosphate and silicate limited conditions. The triacylglycerols (TAGs), important for biofuel production, are increasing most under nutrient limited conditions. The longer fatty acids, for example eicosapentaenoic (EPA, C20:5) and docosahexaenoic (DHA, C22:6), also known as fish oils, are decreasing in nutrient limited conditions. This is because the diatom is switching from longer chains of fatty acids to shorter chains that can be stored as neutral lipids in the vacuole. The carbohydrates increase under nitrate and phosphate limited conditions. The amount of extracellular carbohydrates and cellular changes between species and is not dependent on nutrient limitation. The increase in carbohydrates takes care of an increases in their sinking rate. They are able to sink out of the euphotic zone, when conditions are unfavourable. They sink below the nutricline and stay there in a resting state. They re-enter the euphotic zone due to vertical mixing or replenishing of the limited nutrients, were they use the carbohydrates as an energy source to accumulate the nutrients. With silicate limitation the amount of carbohydrates is decreased. The sinking rate is increased by a change in morphology under silicate limitation. They use lipids for their energy storage. When returned to favourable conditions, lipids are used for growth. In conclusion the total amount of lipids increases under nutrient limitation and the total amount of carbohydrates increases under nitrate and phosphate limitation but not under silicate limitation.