Evaluation of Thirty Microalgal Isolates as Biodiesel Feedstocks Based on Lipid Productivity and Triacylglycerol (TAG) Content.

Microalgae are considered feedstock for biodiesel production due to their capability to accumulate triacylglycerols, which have a 99% conversion rate into biodiesel, under certain conditions. This study aims to evaluate thirty native microalgal strains as feedstock for biodiesel production based on their biomass and lipid productivities, and total lipid and triacylglycerol contents under nitrogen-sufficient and nitrogen starvation conditions. In addition, Chlamydomonas reinhardtii cw15 mutant strain was utilized as a reference strain for triacylglycerol accumulation. Among the eight potent strains, Chlorella vulgaris KP2 was considered as a most promising strain with the highest triacylglycerol content, highest total lipid content (28.56% of dry cell weight), and the highest lipid productivity (4.56 mg/L/day) under nitrogen starvation. Under nitrogen starvation, the major fatty acids in the triacylglycerol of Chlorella vulgaris KP2 were C18:1 (37.56%), C16:0 (23.16%), C18:0 (23.07), C18:2 (7.00%), and C18:3 (3.12%), and the percentages of saturated fatty acids, monounsaturated fatty acids, and polyunsaturated fatty acids represented 49.26, 38.73, and 10.12% of the total fatty acids, respectively. Furthermore, the fatty acid methyl esters of triacylglycerol displayed remarkable biodiesel properties with a lower iodine value (59.00 gI2/100 g), higher oxidative stability (14.24 h) and higher cetane number (58.73) under nitrogen starvation. This study suggests that nitrogen-starved Chlorella vulgaris KP2 could be used as a feedstock for biodiesel production due to the considerable amounts of triacylglycerol and favorable biodiesel properties.

The evaluation of Starmerella magnoliae X3 as a biodiesel feedstock based on triacylglycerol (TAG) production, lipid productivity, and fatty acid profile under nitrogen limitation and acidic pH conditions.

The effects of four initial culture pH values (3, 4, 5, and 6) and nitrogen limitation on growth, TAG accumulation, lipid production, fatty acid profile, and estimated biodiesel quality of Starmerella magnoliae X3 were investigated. TAG and lipid levels were measured by Nile Red fluorescence and sulfo-phospho-vanilin (SPV) techniques, respectively. The results showed that a combination of nitrogen limitation and acidic pH significantly (p < 0.05) increased TAG accumulation, total lipid contents, and lipid productivity in Starmerella magnoliae X3 compared to the control group. Under nitrogen limitation, the highest TAG accumulation was achieved at initial pHs of 3 and 5 after 72 h of cultivation, and the highest lipid productivity (0.306 g L-1 d-1) was observed after 48 h at pH 3; the major fatty acids at the four pH values were oleic acid (63.6%-64%), palmitoleic acid (11.3%-12.5%), stearic acid (9.7%-11.4%), and palmitic acid (9.4%-10%). In addition, both stresses were associated with lower iodine value and higher cetane number of the biodiesel compared to the control. These findings suggest that cultivation in a low-nitrogen medium at an initial pH of 3 or 5 holds promise in increasing TAG production in Starmerella magnoliae X3.

Antiproliferative, neurotoxic, genotoxic and mutagenic effects of toxic cyanobacterial extracts.

Cyanobacteria are the rich resource of various secondary metabolites including toxins with broad pharmaceutical significance. The aim of this work was to evaluate the antiproliferative, neurotoxic, genotoxic and mutagenic effects of cyanobacterial extracts containing Microcystin-LR (MCLR) in vitro. ELISA analysis results showed that MCLR contents of five cyanobacterial extracts were 2.07 ng/mL, 1.43 ng/mL, 1.41 ng/mL, 1.27 ng/mL, and 1.12 ng/mL for Leptolyngbya sp. SB1, Phormidium sp. SB4, Oscillatoria earlei SB5, Phormidium sp. SB2, Uncultured cyanobacterium, respectively. Phormidium sp. SB4 and Phormidium sp. SB2 extracts had the lowest neurotoxicity (86% and 79% cell viability, respectively) and Oscillatoria earlei SB5 extracts had the highest neurotoxicity (47% cell viability) on PC12 cell at 1000 µg/ml extract concentration. Leptolyngbya sp. SB1 and Phormidium sp. SB2 showed the highest antiproliferative effect (92% and 77% cell death) on HT29 cell. On the other hand, all concentrations of five toxic cyanobacterial extracts induced DNA damage between 3.0% and 1.3% of tail intensity and did not cause any direct mutagenic effect at the 1000 µg/plate cyanobacterial extracts. These results suggest that cyanobacteria-derived MCLR is a promising candidate for development of effective agents against colon cancer.

Determination of the potential of Pistia stratiotes L. in removing nickel from the environment by utilizing its rhizofiltration capacity

Abstract: The aim of this study is to explain the biological response and rhizofiltration capacity of Pistia stratiotes, which is an aquatic macrophyte, in alleviating heavy metal stress. In our study, Pistia species were exposed to Nickel (Ni) at different concentrations over seven days. The potential of the aquatic macrophytes in accumulating heavy metals in the water and in removing them from the environment was evaluated by determining the bio-concentration factors (BCF). Selected biological parameters in the leaves of Pistia stratiotes, including metal accumulation, photosynthetic pigment amount, lipid peroxidation activity, and growth rates were measured at the end of the seven-day period. The highest amount of Ni accumulation in P. stratiotes occurred at a concentration of 20 mg l-1. The amount of chlorophyll a (chl a) in P. stratiotes reached a value of 0.087 mg g-1 at the Ni concentration of 20 mg l-1. The relative growth rate (RGR) of P. stratiotes showed a negative correlation with the increases in the concentration levels of the metal. Malondialdehyde (MDA) levels increased to 8.214 nmol/g at the concentration of 20 mg l-1, depending on Ni concentration and time. In our study, the use of P. stratiotes has been determined to be an appropriate plant as an effective Ni accumulator to be utilized with the purpose of rhizofiltration.