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Marine organisms are a valuable source of new compounds, many of which have remarkable biotechnological properties, such as microalgae and cyanobacteria, which have attracted special attention to develop new industrial production routes. These organisms are a source of many biologically active molecules in nature, including antioxidants, immunostimulants, antivirals, antibiotics, hemagglutinates, polyunsaturated fatty acids, peptides, proteins, biofuels, and pigments. The use of several technologies to improve biomass production, in the first step, industrial processes schemes have been addressed with different accomplishments. It is critical to consider all steps involved in producing a bioactive valuable compound, such as species and strain selection, nutrient supply required to support productivity, type of photobioreactor, downstream processes, namely extraction, recovery, and purification. In general, two product production schemes can be mentioned; one for large amounts of product, such as biodiesel or any other biofuel and the biomass for feeding purposes; the other for when the product will be used in the human health domain, such as antivirals, antibiotics, antioxidants, etc. Several applications for microalgae have been documented. In general, the usefulness of an application for each species of microalgae is determined by growth and product production. Furthermore, the use of OMICS technologies enabled the development of a new design for human therapeutic recombinant proteins, including strain selection based on previous proteomic profiles, gene cloning, and the development of expression networks. Microalgal expression systems have an advantage over traditional microbial, plant, and mammalian expression systems for new and sustainable microalga applications, for responsible production and consumption.

This study was parametrically established to investigate the effect of different initial pH cultivation medium from pH 4.00 to pH 10.00 and CO2 concentration from 0.04% to 25% (v/v) on the growth and carbohydrate content of Halochlorella rubescens. Changes in biochemical compositions were also analysed using Fourier-transform infrared spectroscopy (FTIR). The maximum concentration of biomass and the productivity carbohydrate were 0.49 ± 0.01 g/L and 22.42 ± 0.03 mg/L.d respectively, when pH 10.00 and 5% (v/v) CO2 concentration were used for cultivation. The FTIR analysis revealed obvious changes in the chemical functional groups for the1200-900 cm-1, 1655 cm-1 and 2850 cm-1 bands, which represent carbohydrate, protein and lipid in microalgal biomass under different cultivation conditions. At the completion of this study, two kinetic growth models, Logistic and Gompertz were evaluated for microalgae growth at elevated condition. The kinetic model analysis for Halochlorella rubescens growth at high CO2 condition fit well with the Gompertz equation with R²value of 0.9977. The data acquired from this research was helpful for predicting the growth characteristics of microalgae in a CO2-rich medium and could act as an essential platform for the production of chemicals and biofuels. [ABSTRACT FROM AUTHOR]