Aims: Variation in the traditional growth medium conditions to enhance the production of lipids, carbohydrates, protein and the free amino acids content of three cyanobacterial species. Methodology and Results: Three species of cyanobacteria (Anabaena laxa, Anabaena fertilissima and Nostoc muscorum) were collected from the culture collection of Soils, Water and Environment Research Institute, Agriculture Research Center, Giza, Egypt, to investigate their biochemical composition under different growth conditions, using BG110 (nitrogen free) as growth medium. These conditions were represented by control medium, static glucose medium with (1%, w/v), aerated medium (aerated by bubbling technique depending on CO2 normally existed in air with a concentration of 0.03%), molasses medium (0.7%, v/v) and aerated medium enriched with glucose (1%, w/v). Lipid content, total carbohydrates, soluble proteins and free amino acids were determined at the previous conditions. Glucose at 0.7% (w/v) was the most favorable for lipid production in A. laxa, where it exhibited the highest lipid content (427 µg/g fresh wt.). Increasing molasses concentration up to 0.7% (v/v) produced an increase in lipid contents of the tested cyanobacterial strains. The highest lipid content of both N. muscorum (366.2 µg/g fresh wt.) and A. laxa (357.4 µg/g fresh wt.) were recorded at molasses concentrations of 0.1 and 0.7% (v/v), respectively. A. laxa expressed high significant values for both proteins (31.6 µg/mL) and free amino acids (40.5 mg/g dry wt.) after 6 days of incubation period under aerated enriched glucose condition (1%, w/v). Also, at the same growth conditions, A. fertilissima exhibited high significant values for carbohydrates at 4 th day (876.8 mg/g dry wt.). Conclusion, significance and impact of study: Aerated enriched glucose medium (1%, w/v) was the best growth medium condition used in the present study.

The present study is a trial to cultivate three different cyanobacterial strains (Anabaena laxa, Anabaena fertilissima and Nostoc muscorum) under four different growth conditions using BG11 0 growth medium. These conditions are represented by static glucose medium with glucose (1%, w/v), aerated medium (aerated by bubbling technique depending on atmospheric CO 2 normally existed in air with a concentration of 0.3%), growth medium enriched with molasses of sugar cane (0.7%, v/v) and aerated growth medium enriched with glucose (1%, w/v). A. laxa, A. fertilissima and N. muscorum exhibited high biomass production under mixotrophic growth condition rather than aerated autotrophic condition. Whereas, static glucose medium enhanced the growth of A. laxa, A. fertilissima and N. muscorum significantly with dry weight yield of 3.6, 3.1 and 5.2 g L-1 , respectively. Moreover, glucose enhanced lipid content for both A. laxa and N. muscorum to produce 293.9 and 253.5 μg g-1 fresh wt., respectively. While A. fertilissima exhibited the highest lipid content under aerated enriched glucose medium (307.6 μg g-1 fresh wt.). Static glucose medium supported the lipid synthesis rate of N. muscorum to record 6.3 folds, as compared to the control, after 10 days of treatment. While A. fertilissima exhibited its highest lipid synthesis rate under aerated enriched glucose condition after 2 days. Ten fatty acids were detected for all the investigated cyanobacterial strains with different percentages, under static glucose medium (1%, w/v) during the stationary phase. Half of them were saturated fatty acids and the others were two mono-unsaturated and three poly-unsaturated fatty acids. Myristic, palmitoleic and arachidonic acids were the most abundant among all the tested isolates.