Application of Response Surface Method for Studying the Role of Dissolved Oxygen and Agitation Speed on Gamma-Linolenic Acid Production

Evaluation of Different Standard Amino Acids to Enhance the Biomass, Lipid, Fatty Acid, and γ-Linolenic Acid Production in Rhizomucor pusillus and Mucor circinelloides

In this study, 18 standard amino acids were tested as a single nitrogen source on biomass, total lipid, total fatty acid (TFA) production, and yield of γ-linolenic acid (GLA) in Rhizomucor pusillus AUMC 11616.A and Mucor circinelloides AUMC 6696.A isolated from unusual habitats. Grown for 4 days at 28°C, shaking at 150 rpm, the maximum fungal biomass for AUMC 6696.A was 14.6 ± 0.2 g/L with arginine and 13.68 ± 0.1 g/L with asparagine, when these amino acids were used as single nitrogen sources, while AUMC 11616.A maximum biomass was 10.73 ± 0.8 g/L with glycine and 9.44 ± 0.6 g/L with valine. These were significantly higher than the ammonium nitrate control (p < 0.05). The highest levels of TFA were achieved with glycine for AUMC 11616.A, 26.2 ± 0.8% w/w of cell dry weight, and glutamic acid for AUMC 6696.A, 23.1 ± 1.3%. The highest GLA yield was seen with proline for AUMC 11616.A, 13.4 ± 0.6% w/w of TFA, and tryptophan for AUMC 6696.A, 12.8 ± 0.3%, which were 38% and 25% higher than the ammonium tartrate control. The effects of environmental factors such as temperature, pH, fermentation time, and agitation speed on biomass, total lipids, TFA, and GLA concentration of the target strains have also been investigated. Our results demonstrated that nitrogen assimilation through amino acid metabolism, as well as the use of glucose as a carbon source and abiotic factors, are integral to increasing the oleaginicity of tested strains. Few studies have addressed the role of amino acids in fermentation media, and this study sheds light on R. pusillus and M. circinelloides as promising candidates for the potential applications of amino acids as nitrogen sources in the production of lipids.

Comparative Analysis of Different Isolated Oleaginous Mucoromycota Fungi for Their γ-Linolenic Acid and Carotenoid Production

γ-Linolenic acid (GLA) and carotenoids have attracted much interest due to their nutraceutical and pharmaceutical importance. Mucoromycota, typical oleaginous filamentous fungi, are known for their production of valuable essential fatty acids and carotenoids. In the present study, 81 fungal strains were isolated from different Egyptian localities, out of which 11 Mucoromycota were selected for further GLA and carotenoid investigation. Comparative analysis of total lipids by GC of selected isolates showed that GLA content was the highest in Rhizomucor pusillus AUMC 11616.A, Mucor circinelloides AUMC 6696.A, and M. hiemalis AUMC 6031 that represented 0.213, 0.211, and 0.20% of CDW, respectively. Carotenoid analysis of selected isolates by spectrophotometer demonstrated that the highest yield of total carotenoids (640 μg/g) was exhibited by M. hiemalis AUMC 6031 and M. hiemalis AUMC 6695, and these isolates were found to have a similar carotenoid profile with, β-carotene (65%), zeaxanthin (34%), astaxanthin, and canthaxanthin (5%) of total carotenoids. The total fatty acids of all tested isolates showed moderate antimicrobial activity against Staphylococcus aureus and Salmonella Typhi, and Penicillium chrysogenum. To the best of our knowledge, this is the first report on the highest yield of total lipid accumulation (51.74% CDW) by a new oleaginous fungal isolate R. pusillus AUMC 11616.A. A new scope for a further study on this strain will be established to optimize and improve its total lipids with high GLA production. So, R. pusillus AUMC 11616.A might be a potential candidate for industrial application.

Aeration effect on Spirulina platensis growth and γ-Linolenic acid production

The influence of aeration on algal growth and gamma-linolenic acid (GLA) production in a bubble column photobioreactor was investigated. Studies were performed in a 20-L reactor at different aeration rates (0.2– 2.5 vvm). Static, continuous, and periodic operation of air resulted in 41.9%, 88.4%, and 108% air saturation of dissolved oxygen, for which the corresponding values of GLA were 2.3, 6.5, and 7.5 mg·g^-1 dry cell weight, respectively. An increase in the aeration rate from 0.2 to 2.5 vvm enhanced both the specific growth rate and GLA content under periodic sparging in the bicarbonate medium. With a 6-fold increase in the aeration rate, the GLA content of the alga increased by 69.64% (5.6–9.5 mg· g^-1 dry cell weight). In addition, the total fatty acid (TFA) content in dry biomass increased from 2.22% to 4.41%, whereas the algae maintained a constant GLA to TFA ratio within the aeration rate tested. The dependence of GLA production on the aeration rate was explained by interrelating the GLA production rate with the specific growth rate using the Luedeking and Piret mixed growth model.