Research stimulated by curiosity brings out new pieces that make up the puzzle of life and invention provide the tools to assemble and interpret it. The Industrial Revolution of past centuries has brought innovations not accompanied by a far- sighted vision of the consequences that are manifesting in this globalized twenty-first century, particularly with an increase in energy demand and global warming. The

emerging biotechnology revolution, which applies technology to biological systems, could solve these problems without further deleterious effects if driven by sustainable development. Research and development institutes, subsidized by governments, are looking for renewable and sustainable energy resources that would replace polluting fossil fuels nearly depleted. Recently the investigation of the marine microalgae's potential in biotechnological applications is increasing by the realization that the ocean is a relatively untapped source of energy biomass and novel biomolecules. Microalgae mainly represent the last generation suitable feedstock for the transport sector, but due to their biochemical versatility are useful also for many other industrial fields such as medical, pharmaceutical, food and cosmetic. Nowadays, biofuel production from microalgae biomass is still in progress; the efficiency of each step during the whole process, from culturing to refining, needs to be improved to get yield economically reasonable. Coupling each other different industrial applications could lead to overcome the substantial investments with proper earnings making, hopefully in the next future, this living energy source lucrative, therefore commercially feasible. In the last decades, researchers are focusing their attention on Diatoms, a taxon of microalgae characterized by silica walls derived from secondary symbiotic event. Diatoms are affected by seasonal exponential growth called blooms that place them

at the base of the oceans food chain, permit about 40% of atmospheric CO 2 fixation and significant influence the biogeochemical cycle of the macronutrients: silicon (Si), nitrogen (N), phosphorus (P). This microalgae's group is a promising candidate for biodiesel production because of their great lipid accumulation like reserve storage compound mainly in the form of triacylglycerols (TAG), converted into biodiesel through a reaction of trans-esterification. The aim of this thesis were the evaluation of the growth curves and biochemical composition (lipids, carbohydrates and proteins) of the marine diatom Cyclotella Cryptica grown in batch system by administering the average of the standard medium

f / 2 daily or only the day of the inoculation. The growth curve was obtained bymonitoring daily the cellular density (cells / mL) with an optical microscope combined with a Bürker chamber. The biological macromolecules quantification, lipids, carbohydrates, and proteins were realized by Folch modified - MTBE, Dubois and Lowry methods, respectively. Furthermore, the lipids composition was characterized both by Thin Layer Chromatography (TLC) and Nuclear Magnetic Resonance (NMR) -Eretic method.

The results show that the daily supply of the medium f / 2 induces high cell density (2250000 ± 77567 cells / mL) and biomass dry weight (1441.79 ± 148.35 mg / L) that mainly consist of proteins (88%) and lipid fraction is predominantly composed by phospholipids (PL). Conversely, administering the medium f / 2 only the first day let the diatoms in a starvation condition defined by a little cell density (192222 ± 26851) and biomass dry weight (205.90 ± 22.24 mg / L) with a significant increase in the relative amount of storage compounds: carbohydrates (19%) and lipid (33%) predominantly in form of triacylglycerols (TAG). Typically, microalgae are growth at first in laboratories under strict controlled condition in closed photobioreactors and then transferred to open-pounds for large-scale production. The main traits to assess the microalgae productivity for biodiesel production is based on the selection of the strain that accomplish the trade-off between elevated growth rate and neutral lipids accumulation. Hence, the two experimental culture conditions evaluated in this work could be useful to establish a sequential protocol of growth for large volume system. Furthermore, the cells enriched in protein could be a suitable feedstock in agriculture, aquaculture or for a breeding farm.