Identification and evaluation of freshwater green microalgae (chlorophyceae) for production of biodiesel, animal feeds, and bioactive compounds

Two freshwater green microalgal strains (I-AUI and U-AU2) isolated in soil sample from Bukidnon and Los Baños, Laguna [Philippines] were selected for this study. The phenotypic features of the two isolates showed the existence of both unicellular and colonial forms. Molecular identification of the algal strains usind rRNA showed closest similarity to Desmodesmus spp. whereas the phylogenetic analyses clustered them together with other Desmodesmus spp. and away from Scenedesmus spp. Comparative analysis of the effects of different concentrations of nitrogen source (0.375-1.50 g/L NaNO3) on growth oil yield, lipid productivity and fatty acid profile composition of the two algal strains were studied. After 22 days of cultivation, highest lipid accumulations on both algal strains were recorded in the culture with 0.375 g/L NaNO3, which is only one fourth of the basal nitrogen source concentration. Maximum average biomass yield and lipid productivity for Desmodesmus sp. (U-AU2) were 1.54 g/L and 19.06 mg/L/d (that is 27.23% lipid content per dry weight of biomass), respectively, with a specific growth rate of 0.18/day. On the other hand, Desmodesmus sp. (I-AU1) was found to have 1.54 g/L and 19.06 mg/L/d (that is 27.23% lipid content per dry weight of biomass, respectively, with a specific growth rate of 0.18/day. On the other hand, Desmodesmus sp. (I-AU1) was found to have 1.51 g/L and 27.83 mg/L/d (that is 4.54% lipid content per dry weight of biomass), respectively, with a specific growth rate of 0.29/day. It was observed for both strains that as the nitrate concentration in the medium decreased, biomass production also decreased but the lipid content increased. Fuel properties were determined by empirical equations and found to be within the limits of biodiesel standard of ASTM D6751 and EN 14214. Proximate analyis of the dried microalgal biomass showed that Desmodesmus sp. (U-AU2) showed high protein content that I-AU1 having 49.95+-0.02% and 34.69+-0.41 respectively. Protein level that ranged from about 34% to nearly 50% of cellular dry weight was observed in this study providing the possibility of using these two green microalgal strains as alternative sources of protein for feed production. Methanolic estracts of each of the algal strain (I-AU1 and U-AU2) were subjected ti antimicrobial assays against a wide spectrum of microorganisms. U-AU2) were subjected to antimicrobial assays against a wide spectrum of microorganism. U-AU2 exhibited pronounced activity against Gram-positive bacteria, Staphylococcus aureus with MIC and MBC of 31.25 and 125.00 mug/ml, respectively. It was moderately active against Listeria monocytogenes, Methicillin-Resistant Staphylococus aureus and Pseudomonas aeruginosa (both MIC = 250 mug/ml) as well as Aeromonas hydropila (both MIC = 1000 mug/ml). Minimum bactericidal activity of 1000 mug/ml was observed against Listeria monocytogenes, Methicillin-Resistant S. aureus, Aeromonas hydrophila and P. aeruginoa. On the other hand, Desmodesmus sp. I-AU1 showed antimicrobial activity against S. aeruginosa each having MIC of 250 mug/ml. L. monocytogenes and Methicilin-resistant S. aureus were also moderately inhibited each having MIC of 1000 mug/ml. Minimum bactericidal activity of S. aureus is higher than that of P. Aeruginosa, having 500 mug/ml and 1000 mug/ml, respectively. On the other hand L. manocytogenes and Metchilin-resistant S. aureus exbibited MBC of 1000 mug/ml. The reproducibility of this finding was confirmed by using the cylinder cup assay. Results of the cylinder cup assay showed that the algal cultures were able to exhibit zone of inhibition. Desmodesmus sp (U-AU2) exhibited zones of inhibition ranging from 13.00 to 14.00 mm against S. aureus while Desmodesmus sp. (I-AU1) showed zones of inhibition ranging from 8.00 to 9.00 mm on the same organism. In addition to this, Desmodesmus sp (U-AU2) showed zones of inhibition ranging from 14.00 to 15.00 mm against Methicillin-Resistant Staphylococcus aureus. Total phenolic content was determinant using Folin-Ciocalteu reagent in terms of gallic acid equivalents (GAE). Antioxidant activity was evaluated using diphenyl-12-picry1 hydrazyl (DPPH) free radical scavenging activity assay and reduction of copper ions using the CUPRAC assay. Total phenolic content was observed to be higher in Desmodesmus sp. (U-AU2) than in I-AU1 having phenolic concentration of 652.66 mug GAE/ml and 606.91 mug GAE/ml, respectively. Relative antioxidant efficiency showed that Desmodesmus sp. (I-AU1) having phenolic concentration of 652.66 mug GAE/ml and 606.91 mug GAE/ml, respectively. relative antioxidant efficiency showed that Desmodesmus sp. (U-AU2) exerted more potent radical scavenging activity that Desmosdesmus sp (I-AUI). The same trend was observed for the CUPRAC assay. Methanolic extract of the algal samples showed the ability of reducing copper irons from CU(2) to CU (1) in a concentration dependent manner. The results further revealed that the copper iron chelating ability as well as the radical scavenging activity of the extracts were dose-dependent and positively correlated to their phenolic content. The results of this study showed that the two strains of microalgae (Desmodesmus sp. strains I-AU2) are suitable candidates for biodiesel production while its protein rich biomass can be used as feedstock for animal feeds. Moreover, the biomass of these microalgal strains can be used as alternative raw materials for pharmaceutical industry.