Mathias Ahii Chia

Lipid composition of Chlorella vulgaris (Trebouxiophyceae) as a function of different cadmium and phosphate concentrations

Fatty acids are the fundamental structural components of membrane lipids, and the degree of saturation of the long hydrocarbon chains in microalgae contributes to regulation of growth, biomass production and reproduction of aquatic consumers. This research aimed at evaluating the effects of cadmium (2×10(-8); 10(-7) mol L(-1) Cd) on lipid class and fatty acid composition of the microalga Chlorella vulgaris under varying phosphate (PO(4)(3-)) concentrations (6.0×10(-7) to 2.3×10(-4) mol L(-1)). Under PO(4)(3-) limitation and Cd stress, the storage lipid class triacylglycerol (TAG) was the most accumulated among the lipid classes. Fatty acid composition revealed that the degree of saturation increased with increasing Cd stress and PO(4)(3-) limitation. Decreasing PO(4)(3-) and increasing Cd concentrations resulted in higher saturated fatty acid (SAFA) and monounsaturated FA (MUFA) concentrations. Total polyunsaturated FA (PUFA) and ω3 PUFA, and PUFA:SAFA ratios were higher in the control (2.3×10(-4) mol L(-1) PO(4)(3-)) cells than in either PO(4)(3-) limitation or Cd stress, or in the combination of both stresses. Contrasting with all the other PUFAs, 18:2n - 6 increased as PO(4)(3-) limitation increased. A significant positive relationship of PUFAs, acetone mobile polar lipids (AMPL) and phospholipids (PL) with phosphate concentration in the culture media was obtained, while TAG concentrations had a positive association with total MUFA and SAFA. Total SAFA, 14:0, 18:1n - 9 and 18:2n - 6 were positively correlated with Cd and negatively with PO(4)(3-) concentrations. The microalga responded to combined PO(4)(3-) limitation and Cd exposure by increasing its total lipid production and significantly altering its lipid composition. The FA 18:2n - 6 may be considered a stress biomarker for PO(4)(3-) limitation and Cd stress in C. vulgaris.

Effects of cadmium and nitrogen on lipid composition of Chlorella vulgaris (Trebouxiophyceae, Chlorophyta)

Investigations were carried out to evaluate lipid class and fatty acid composition of Chlorella vulgaris in relation to several combinations of cadmium (2u2009×u200910−8; 10−7u2009M Cd) and nitrogen (2.9u2009×u200910−6 to 1.1u2009×u200910−3 M N) concentrations. Triacylglycerols (TAG), acetone mobile polar lipids (AMPL) and phospholipids (PL) were the major lipid classes of C. vulgaris under all the tested conditions. TAG was the lipid class accumulated in the highest amount in N-limited C. vulgaris. The AMPL lipid class was lowest at the lowest N and highest Cd treatment. High proportions of saturated fatty acids (SAFA) and monounsaturated fatty acids (MUFA) in the total lipid extracts were recorded under N limitation in the presence of Cd. 16:1(n-11) was an exception among the MUFA as its levels decreased at low N. Total polyunsaturated FA (PUFA), ω3 PUFA levels, and PUFA:SAFA ratios increased with increasing N concentrations, but when exposed to Cd, their levels were significantly reduced. Unlike the other PUFA, 18:2(n-6) increased with increasing N limitation. Significant negative relationships between TAG, MUFA and SAFA with N were recorded. Cd had a positive correlation with TAG, while N was with AMPL, PL and PUFA. In conclusion, a combination of N limitation and Cd stress significantly altered the lipid composition of C. vulgaris, and N limitation had the most significant overall effect on lipid class and fatty acid composition of the microalga.

Allelopathic interactions between microcystin-producing and non-microcystin-producing cyanobacteria and green microalgae: implications for microcystins production

Most mixed culture studies on the allelopathic interactions between toxic and nontoxic cyanobacteria with phytoplankton species rarely investigate the role of microcystins (MC) production and regulation in the course of the studies. This study investigated the interactions between intact cells of toxic (Microcystis aeruginosa (Kützing) Kützing) and nontoxic (Microcystis panniformis Komárek et al.) cyanobacteria with those of green algae (Monoraphidium convolutum (Corda) Komárková-Legnerová and Scenedesmus acuminatus (Largerheim) Chodat) as well as the effects of their respective crude extracts (5 and 10xa0μg.L−1) on their growth under controlled conditions. M. aeruginosa and M. panniformis were able to significantly (pu2009<u20090.05) inhibit the growth of the green algae with M. convolutum being the most affected. The green alga S. acuminatus in return was able to inhibit the growth of the both cyanobacteria. In response to the presence of a competing species in the growth medium, M. aeruginosa significantly increased its MC production per cell with the progression of the experiment, having the highest concentration at the end of the experiment. On the other hand, the extracts of the cyanobacteria had no significant inhibitory effect on the green algal strains investigated, while those of the green algae also had significant inhibitory effect on the growth of M. aeruginosa. In conclusion, both cyanobacterial and green algal strains investigated were negatively affected by the presence of competing species. M. aeruginosa responded to the presence of green algae by increasing its MC production. The green algal strains significantly inhibited the growth of M. aeruginosa.

Combined nitrogen limitation and cadmium stress stimulate total carbohydrates, lipids, protein and amino acid accumulation in Chlorella vulgaris (Trebouxiophyceae)

Metals have interactive effects on the uptake and metabolism of nutrients in microalgae. However, the effect of trace metal toxicity on amino acid composition of Chlorella vulgaris as a function of varying nitrogen concentrations is not known. In this research, C. vulgaris was used to investigate the influence of cadmium (10(-7) and 2.0×10(-8)molL(-1) Cd) under varying nitrogen (2.9×10(-6), 1.1×10(-5) and 1.1×10(-3)molL(-1)N) concentrations on its growth rate, biomass and biochemical composition. Total carbohydrates, total proteins, total lipids, as well as individual amino acid proportions were determined. The combination of Cd stress and N limitation significantly inhibited growth rate and cell density of C. vulgaris. However, increasing N limitation and Cd stress stimulated higher dry weight and chlorophyll a production per cell. Furthermore, biomolecules like total proteins, carbohydrates and lipids increased with increasing N limitation and Cd stress. Ketogenic and glucogenic amino acids were accumulated under the stress conditions investigated in the present study. Amino acids involved in metal chelation like proline, histidine and glutamine were significantly increased after exposure to combined Cd stress and N limitation. We conclude that N limitation and Cd stress affects the physiology of C. vulgaris by not only decreasing its growth but also stimulating biomolecule production.

Lettuce irrigated with contaminated water: Photosynthetic effects, antioxidative response and bioaccumulation of microcystin congeners

The use of microcystins (MCs) contaminated water to irrigate crop plants represents a human health risk due to their bioaccumulation potential. In addition, MCs cause oxidative stress and negatively influence photosynthetic activities in plants. The present study was aimed at investigating the effect of MCs on photosynthetic parameters and antioxidative response of lettuce. Furthermore, the bioaccumulation factor (BAF) of total MCs, MC-LR and MC-RR in the vegetable after irrigation with contaminated water was determined. Lettuce crops were irrigated for 15 days with water containing cyanobacterial crude extracts (Microcystis aeruginosa) with MC-LR (0.0, 0.5, 2.0, 5.0 and 10.0 µg L(-1)), MC-RR (0.0, 0.15, 0.5, 1.5 and 3.0 µg L(-1)) and total MCs (0.0, 0.65, 2.5, 6.5 and 13.0 µg L(-1)). Increased net photosynthetic rate, stomatal conductance, leaf tissue transpiration and intercellular CO2 concentration were recorded in lettuce exposed to different MCs concentrations. Antioxidant response showed that glutathione S-transferase activity was down-regulated in the presence of MCs. On the other hand, superoxide dismutase, catalase and peroxidase activities were upregulated with increasing MCs concentrations. The bioaccumulation factor (BAF) of total MCs and MC-LR was highest at 6.50 and 5.00 µg L(-1), respectively, while for MC-RR, the highest BAF was recorded at 1.50 µg L(-1) concentration. The amount of total MCs, MC-LR and MC-RR bioacumulated in lettuce was highest at the highest exposure concentrations. However, at the lowest exposure concentration, there were no detectable levels of MC-LR, MC-RR and total MCs in lettuce. Thus, the bioaccumulation of MCs in lettuce varies according to the exposure concentration. In addition, the extent of physiological response of lettuce to the toxins relies on exposure concentrations.

Growth and biochemical composition of Chlorella vulgaris in different growth media

The need for clean and low-cost algae production demands for investigations on algal physiological response under different growth conditions. In this research, we investigated the growth, biomass production and biochemical composition of Chlorella vulgaris using semi-continuous cultures employing three growth media (LC Oligo, Chu 10 and WC media). The highest cell density was obtained in LC Oligo, while the lowest in Chu medium. Chlorophyll a, carbohydrate and protein concentrations and yield were highest in Chu and LC Oligo media. Lipid class analysis showed that hydrocarbons (HC), sterol esthers (SE), free fatty acids (FFA), aliphatic alcohols (ALC), acetone mobile polar lipids (AMPL) and phospholipids (PL) concentrations and yields were highest in the Chu medium. Triglyceride (TAG) and sterol (ST) concentrations were highest in the LC Oligo medium. The results suggested that for cost effective cultivation, LC Oligo medium is the best choice among those studied, as it saved the cost of buying vitamins and EDTA associated with the other growth media, while at the same time resulted in the best growth performance and biomass production.

Effect of indigo dye effluent on the growth, biomass production and phenotypic plasticity of Scenedesmus quadricauda (Chlorococcales).

The effect of indigo dye effluent on the freshwater microalga Scenedesmus quadricauda ABU12 was investigated under controlled laboratory conditions. The microalga was exposed to different concentrations of the effluent obtained by diluting the dye effluent from 100 to 175 times in bold basal medium (BBM). The growth rate of the microalga decreased as indigo dye effluent concentration increased (p <0.05). The EC50 was found to be 166 dilution factor of the effluent. Chlorophyll a, cell density and dry weight production as biomarkers were negatively affected by high indigo dye effluent concentration, their levels were higher at low effluent concentrations (p <0.05). Changes in coenobia size significantly correlated with the dye effluent concentration. A shift from large to small coenobia with increasing indigo dye effluent concentration was obtained. We conclude that even at low concentrations; effluents from textile industrial processes that use indigo dye are capable of significantly reducing the growth and biomass production, in addition to altering the morphological characteristics of the freshwater microalga S. quadricauda. The systematic reduction in the number of cells per coenobium observed in this study further confirms that environmental stress affects coenobium structure in the genus Scenedesmus, which means it can be considered an important biomarker for toxicity testing.

Lead induced antioxidant response and phenotypic plasticity of Scenedesmus quadricauda (Turp.) de Brébisson under different nitrogen concentrations

The induction of antioxidant response and phenotypic plasticity of Scenedesmus quadricauda after exposure to lead (Pb) (3.6u2009×u200910−8 and 3.6u2009×u200910−7xa0M) at different nitrogen (N) concentrations (1.8u2009×u200910−4, 1.8u2009×u200910−5, and 1.8u2009×u200910−6xa0M) was investigated. The growth of the microalga was inhibited with decreasing N and increasing Pb concentrations. N limitation and Pb stress caused a decrease in biomass (cell density, dry weight, and chlorophyll a) production. Superoxide dismutase (SOD), peroxidase (POD), catalase (CAT), and glutathione S transferase (GST) activities generally increased with N limitation and/or increased Pb stress. CAT and POD activities decreased after 48xa0h, even though their activities were still higher than in those in the control, while GST and SOD activities increased throughout the N/Pb stress exposure period. The enzyme activities observed in S. quadricauda showed a significant positive correlation with N/Pb stress. These results imply that aquatic biota may suffer differently from Pb toxicity, depending on the amount of nitrogen in the environment.

Effects of Cr III and Pb on the bioaccumulation and toxicity of Cd in tropical periphyton communities: Implications of pulsed metal exposures.

Metal exposure pattern, timing, frequency, duration, recovery period, metal type and interactions, has obscured effects on periphyton communities in lotic systems. The objective of this study was to investigate the effects of intermittent exposures of Cr III and Pb on Cd toxicity and bioaccumulation in tropical periphyton communities. Natural periphyton communities were transferred to artificial stream chambers and exposed to metal mixtures at different pulse timing, duration, frequency and recovery periods. Chlorophyll a, dry mass and metal accumulation kinetics were recorded. Cr and Pb decrease the toxic effects of Cd on periphyton communities. Periphyton has high Cd, Cr and Pb accumulation capacity. Crxa0and Pb reduced the levels of Cd sequestrated by periphyton communities. The closer the frequency and duration of the pulse is to a continuous exposure, the greater the effects of the contaminant on periphyton growth and metal bioaccumulation. Light increased toxic and accumulative effects of metals on the periphyton community.

Microcystin-LR bioaccumulation and depuration kinetics in lettuce and arugula: Human health risk assessment

Microcystin-LR (MC-LR) is one of the most toxic and common microcystins (MCs) variant found in aquatic ecosystems. Little is known about the possibility of recovering microcystins contaminated agricultural crops. The objectives of this study were to determine the bioaccumulation and depuration kinetics of MC-LR in leaf tissues of lettuce and arugula, and estimate the total daily intake (ToDI) of MC-LR via contaminated vegetables by humans. Arugula and lettuce were irrigated with contaminated water having 5 and 10μgL(-1) of MC-LR for 7days (bioaccumulation), and subsequently, with uncontaminated water for 7days (depuration). Quantification of MC-LR was performed by LC-MS/MS. The one-compartment biokinetic model was employed for MC-LR bioaccumulation and depuration data analysis. MC-LR was only accumulated in lettuce. After 7days of irrigation with uncontaminated water, over 25% of accumulated MC-LR was still retained in leaf tissues of plants treated with 10μgL(-1) MC-LR. Total daily toxin intake by adult consumers (60kg-bw) exceeded the 0.04μgMC-LRkg(-1) limit recommended by WHO. Bioaccumulation was found to be linearly proportional to the exposure concentration of the toxin, increasing over time; and estimated to become saturated after 30days of uninterrupted exposure. On the other hand, MC-LR depuration was less efficient at higher exposure concentrations. This is because biokinetic half-life calculations gave 2.9 and 3.7days for 5 and 10μgL(-1) MC-LR treatments, which means 29-37days are required to eliminate the toxin. For the first time, our results demonstrated the possibility of MC-LR decontamination of lettuce plants.