Production of lipids and proteins from marine diatoms under changing pH and silica.

Diatom algae are increasingly explored as an alternative sustainable source for functional biomolecules likes fucoxanthin, and eicosapentaenoic acid. But biomolecule quantity and quantity are influenced by growth conditions. So, effect of differential silica concentration (0-120 mg L-1) and medium pH (5.5-9.5) on growth and cellular biochemical composition of commercially important marine diatom species were studied. Growth rate of Thalassiosira sp., Skeletonema sp., and Chaetoceros sp., was higher with 30 mg L-1 Si at a pH of 7.5-8.5. Highest carbohydrate (153.71 mg g-1) and protein (17.34 mg g-1) content was found in Skeletonema sp. Silica concentration positively influenced chlorophyll and carotenoid content in a dose dependent manner. A medium pH of 8.5 and Si concentration between 60 and 120 mg L-1 was ideal for lipid production. The optimum concentration of Si and pH for maximum biomolecule production have been reported with further scope of utilizing these conditions in commercial scale systems.

Bioprospecting of marine diatoms Thalassiosira, Skeletonema and Chaetoceros for lipids and other value-added products.

Diatoms are a major storehouse of valuable fucoxanthin and polyunsaturated fatty acids, with enormous nutraceuticals and biofuel potential. Three marine diatom species isolated from the southern coast of India has been screened and their results show that highest biomass concentration and fucoxanthin yield was obtained in Chaetoceros sp. as 0.217 g L-1 and 0.403 mg L-1 respectively. Lipid % as dry cell weight was maximum in Thalassiosira sp. (52%) followed by Skeletonema sp. (44%) and Chaetoceros sp. (22%). However, protein and secondary metabolites content besides the total antioxidant activity was estimated highest in Skeletonema sp. Having strong inhibition zones of 18-20 mm against all the five strains of bacteria also highlights the highest antibacterial prospect in Skeletonema sp. This work manifests the plasticity of diatoms and may provide useful insights for further species-specific selection for large-scale production of eicosapentaenoic acid, docosahexaenoic acid, fucoxanthin and other metabolites with potential health benefits.

Diatom mediated heavy metal remediation: A review.

Exposure to heavy metals is a major threat to aquatic bodies and is a global concern to our four main spheres of the earth viz. atmosphere, biosphere, hydrosphere, and lithosphere. The biosorption of pollutants using naturally inspired sources like microalgae has considerable advantages. Diatoms are the most dominant and diverse group of phytoplankton which accounts for 45% oceanic primary productivity. They perform a pioneer part in the biogeochemistry of metals in both fresh and marine water ecosystems. The diatoms play a significant role in degradation, speciation, and detoxification of chemical wastes and hazardous metals from polluted sites. Herein, an overview is presented about the ability of diatom algae to phycoremediate heavy metals by passive adsorption and active assimilation from their aqueous environments with an emphasis on extracellular and intracellular mechanisms involved in contaminant uptake through the frustules for preventing heavy metal toxicity.