A MEMBRANE METHOD FOR DETERMINATION OF TOTAL PROTEIN IN DILUTE ALGAL SUSPENSIONS

Phytotoxic, cytogenotoxic, and insecticidal activities of compounds from extracts of freshwater Lyngbya sp

The development of agroecology has promoted the discovery of new bioactive compounds that might act as biocides to control infections and microbial contamination. Algae belonging to Lyngbya genus produce several allelochemicals, which are compounds with crop protection potential. The present study aimed to examine primary and secondary compounds derived from Lyngbya sp. extracts (aqueous and hydroethanolic) on phytotoxic, cytogenotoxic, and insecticidal activities. Determination of compounds indicated the presence predominantly of proteins and flavonoids. The extracts presented physicochemical characteristics that produced (1) 89% germination inhibition using hydroethanolic extract and (2) diminished development of seedlings of L. sativa by hydroethanolic extract as evidenced by reduced radicles length in 83.54%. Aqueous and hydroethanolic Lyngbya sp. extracts significantly interfered with meristematic cells of A. cepa, as evidenced by chromosomal alterations and aberrant mitotic phases in cells. Extracts also exhibited pro-oxidative activity and a potent insecticidal potential on S. zeamais, indicating that the hydroethanolic extract produced 100% insect mortality at 75 mg/ml after 48 hr while the aqueous extract initiated 90% mortality at the same concentration after 82 hr. Therefore, data demonstrate that Lyngbya genus provides basic information for new environmental and ecotoxicological studies to seek a possible source of proteins and flavonoids to be used in agroecological management.

Effects of high temperature and nitrogen availability on the growth and composition of the marine diatom Chaetoceros pseudocurvisetus

The assimilation of inorganic nutrients by phytoplankton strongly depends on environmental conditions such as the availability of nitrogen and temperature, especially warming. The acclimation or adaptation of different species to such changes remains poorly understood. Here, we used a multimethod approach to study the viability and physiological and biochemical responses of the marine diatom Chaetoceros pseudocurvisetus to different temperatures (15, 25, and 30 °C) and different N:P ratios. Nitrogen limitation had a greater effect than high temperature on cell growth and reproduction, leading to a marked elongation of setae, decreased phosphorus assimilation, increased lipid accumulation, and decreased protein synthesis. The elongation of setae observed under these conditions may serve to increase the surface area available for the uptake of inorganic and/or organic nitrogen. In contrast, high temperatures (30 °C) had a stronger effect than nitrogen deficiency on cell death, nitrogen assimilation, chlorophyll a accumulation, the cessation of setae formation, and cell lipid remodelling. Significant changes in thylakoid lipids were observed in cells maintained at 30 °C, with increased levels of digalactosyldiacylglycerol and sulfoquinovosyldiacylglycerol. These changes may be explained by the role of galactolipids in thylakoid membrane stabilization during heat stress.

Inhibition of TOR in Chlamydomonas reinhardtii Leads to Rapid Cysteine Oxidation Reflecting Sustained Physiological Changes

The target of rapamycin (TOR) kinase is a master metabolic regulator with roles in nutritional sensing, protein translation, and autophagy. In Chlamydomonas reinhardtii, a unicellular green alga, TOR has been linked to the regulation of increased triacylglycerol (TAG) accumulation, suggesting that TOR or a downstream target(s) is responsible for the elusive “lipid switch” in control of increasing TAG accumulation under nutrient limitation. However, while TOR has been well characterized in mammalian systems, it is still poorly understood in photosynthetic systems, and little work has been done to show the role of oxidative signaling in TOR regulation. In this study, the TOR inhibitor AZD8055 was used to relate reversible thiol oxidation to the physiological changes seen under TOR inhibition, including increased TAG content. Using oxidized cysteine resin-assisted capture enrichment coupled with label-free quantitative proteomics, 401 proteins were determined to have significant changes in oxidation following TOR inhibition. These oxidative changes mirrored characterized physiological modifications, supporting the role of reversible thiol oxidation in TOR regulation of TAG production, protein translation, carbohydrate catabolism, and photosynthesis through the use of reversible thiol oxidation. The delineation of redox-controlled proteins under TOR inhibition provides a framework for further characterization of the TOR pathway in photosynthetic eukaryotes.

Application of ultrasound for green extraction of proteins from spirulina. Mechanism, optimization, modeling, and industrial prospects

A green and innovative method, manothermosonication (MTS), for proteins extraction from dry Arthrospira platensis cyanobacteria assisted by ultrasound was designed in this work. Manothermosonication (probe, 20 kHz) was compared to a conventional process performed in the same conditions without ultrasounds. The extraction was carried out with a continuous flow rate at 15 mL/hour. Extraction parameters were optimized using a central composite design. Moreover, mathematic modelling and microscopic investigations were realized to allow a better understanding of ultrasound physical and structural effects on spirulina filaments and mass transfer phenomena over time. Crude extract and sections stained with toluidine blue were analyzed with optical and scanning electron microscopies. According to experimental results, MTS promoted mass transfer (high effective diffusivity, D_e) and enabled to get 229% more proteins (28.42 ± 1.15 g/100 g DW) than conventional process without ultrasound (8.63 ± 1.15 g/100 g DW). With 28.42 g of proteins per 100 g of dry spirulina biomass in the extract, a protein recovery rate of 50% was achieved in 6 effective minutes with a continuous MTS process. Microscopic observations showed that acoustic cavitation impacted spirulina filaments by different mechanisms such as fragmentation, sonoporation, detexturation. These various phenomena make extraction, release and solubilization of spirulina bioactive compounds easier.

Characterizing the effect of Poast on Chlorella vulgaris, a non-target organism

Herbicides may cause unexpected damage to non-target organisms as it is challenging to predict undesirable biotic interactions. Poast is a widely used herbicide formulation that contains sethoxydim and targets the acetyl-CoA carboxylase of perennial grasses. In this study, Chlorella vulgaris, a unicellular green microalga, was exposed to a 0.08% working concentration of Poast and the physiological and biochemical changes that took place were monitored using biochemical assays, fluorometry, oximetry, and immunoblotting. Within 15 min, severe photosynthetic damage was observed through a reduction in oxygen production and a reduced rate of electron transfer beyond photosystem II. In addition to direct damage to the photosynthetic machinery, it was shown that cells experienced membrane fragmentation. Within 30 min, over 90% of the exposed cells were nonviable. However, sethoxydim, the active ingredient, did not cause detrimental effects when applied along with mineral spirits, the primary solvent of the formulation. A synergistic or additive effect between sethoxydim and the formulation components cannot be ruled out. This data suggests that Poast has the potential to cause severe harm to unicellular phototrophs in the case of herbicide over application or runoff.

A rapid and general method for measurement of protein in micro-algal biomass

A convenient small-scale extraction method for lyophilized micro-algae is described that dispenses with labor-intensive homogenization and is widely applicable to algae from different phyla. The procedure employs an optimized sequential extraction in trichloroacetic acid (TCA) and NaOH to achieve chemical lysis. Conditions were tested using several micro-algal strains to develop a method that was generally applicable. Incubation of lyophilized material in 24% (w/v) TCA at 95 °C followed by a hot alkaline treatment was found to be effective for strains that are resistant to conventional extraction approaches, such as the Chlorella and the Eustigmatophycean species. The single-tube extraction procedure can be complete in 4h and is conveniently followed by the Lowry assay, requiring a further 30 min. Overall, this method proved to be generally applicable and ideal either for single samples or for high-throughput screening of multiple algal strains for protein content.

Nitrogen fixation by Oscillatoria spp. under autotrophic and photoheterotrophic conditions

Summary: Oscillatoria spp. UCSB8 and UCSB25 are both capable of aerobic N2 fixation. The optimum temperature for C2H2 reduction was 22 °C for Oscillatoria sp. UCSB8 and 35 °C for Oscillatoria sp. UCSB25, whilst the optimum temperature for growth on N2 was 25 °C and 30 °C, respectively. In Oscillatoria sp. UCSB25, but not in UCSB8, inhibition of N2 fixation may limit diazotrophic growth at temperatures above 35 °C. When grown under alternating 12 h light and 12 h darkness, both isolates reduced C2H2 predominantly in the dark and both were capable of N2 fixation and photoheterotrophic growth in the presence of 20 μm-DCMU to inhibit photosystem II activity. Under these conditions, the best exogenous carbon source for Oscillatoria sp. UCSB8 was glucose, whilst that for Oscillatoria sp. UCSB25 was fructose. In Oscillatoria sp. UCSB8, exogenous glucose was catabolized mainly through the oxidative pentose phosphate pathway. Although cultures grown photoheterotrophically showed higher specific activities of nitrogenase than photoautotrophic cultures, they grew more slowly. Furthermore, cultures grown photoheterotrophically under alternating light and darkness reduced C2H2 both in the light and in the dark, but the highest rates of C2H2 reduction were observed in the dark. This cyclic pattern of N2 fixation was independent of photosystem II activity.

Glycerylphosphorylcholine phosphodiesterase in rat liver. Subcellular distribution and localization in plasma membranes

1. A simple new assay for glycerylphosphorylcholine phosphodiesterase is described, in which radioactive glycerylphosphorylcholine is used as substrate and the reaction products are separated by adsorption on an anion-exchange resin. 2. Rat liver subcellular fractions contained both particulate (58%) and soluble (42%) glycerylphosphorylcholine phosphodiesterase. Both activities released free choline from glycerylphosphorylcholine. 3. The particulate glycerylphosphorylcholine phosphodiesterase was recovered mainly in the nuclear and microsomal fractions and showed a distribution similar to those of 5'-nucleotidase and alkaline phosphodiesterase I, both of which are constituents of the liver plasma membrane. 4. During purification of plasma membranes glycerylphosphorylcholine phosphodiesterase, 5'-nucleotidase and alkaline phosphodiesterase I showed largely similar behaviour, indicating that glycerylphosphorylcholine phosphodiesterase is also localized in liver plasma membranes. Slight differences in the distributions of these three enzymes in density-gradient separations are discussed in relation to the possibility that they are unevenly distributed on different areas of the cell surface. 5. The differences between glycerylphosphorylcholine phosphodiesterase and alkaline phosphodiesterase I indicate that these two activities are not functions of a single enzyme. 6. The glycerylphosphorylcholine phosphodiesterase of liver plasma membranes has a pH optimum of 8.5 and a K(m) for glycerylphosphorylcholine of 0.95mm. It is inhibited by EDTA and fully reactivated by a variety of bivalent cations (and Fe(3+)).

Isolation of nuclei from a marine dinoflagellate

By means of a medium containing dextran, nuclei were isolated in high yield from cells of Gymnodinium nelsoni, a marine dinoflagellate. Most of the DNA, but less than onetenth of the RNA, of the original cells was recovered in the purified nuclei. The nuclei appeared substantially intact as observed by light or electron microscopy. The isolated nuclei were capable of incorporating tritiated uridine triphosphate into material insoluble in cold acid. The general procedure was found to be applicable also to two species of diatoms.