Biomass composition of <Emphasis Type="Italic">Arthrospira platensis</Emphasis> during cultivation on industrial process water and harvesting

Microalgae have the ability to utilize nutrients from wastewater and use it for biomass production. The effluent from a biogas process was tested as a nutrient source for blue-green microalga Arthrospira platensis cultivation and compared with conventional synthetic medium. Cultivation was carried out in four different concentrations of industrial process water (25, 50, 75, and 100%). The biomass was then harvested by microfiltration, and centrifugation followed by freeze drying. Variations in biomass composition were studied, in order to investigate effects of industrial process water on A. platensis over 30 days of cultivation. Applied harvesting techniques were evaluated for their effect on physiochemical properties of the biomass. Arthrospira platensis was able to grow in all tested wastewater concentrations except 100%, however, increase of wastewater concentration in medium resulted in a decreased growth rate. Partial substitution of synthetic Zarrouk medium with 25% of wastewater showed no adverse effect on chemical composition of the biomass including high protein content (45–58% dry weight) and favorable fatty acid composition (42–45% PUFAs of total fatty acids). Evaluation by optical microscopy showed that microfiltration caused cell rupture at the moderate level while centrifugation had more severe effect on A. platensis. Effect of centrifugal forces and shear stress on A. platensis cells was confirmed by detecting lower lipid content in samples after applying both microfiltration and centrifugation due to cell content leakage.     

Environmental and spatial filters of zooplankton metacommunities in shallow pools in high‐elevation peatlands in the tropical Andes

相似文献   

DNA replication-blocking properties of adducts formed by aflatoxin B1-2,3-dichloride and aflatoxin B1-2,3-oxide

The carcinogen aflatoxin B1 (AFB1), upon activation to a hypothesized AFB1-2,3-oxide (AFB1-oxide), reacts with DNA guanines. Aflatoxin B1-2,3-dichloride (AFB1-Cl2) was originally synthesized as an electronic analog for the putative AFB1-oxide, which has never been isolated due to presumed reactivity. We have previously shown that AFB1-oxide reacts with base-paired DNA guanines in a sequence-specific manner, as revealed by an alkali-degradation analysis. On the basis of a replication-block analysis, we have shown that AFB1-Cl2 reacts with single-stranded DNA preferentially at inverted repeat sequences, which were suggested to be capable of forming intrastrand base-paired structures. Here, we present data to show the following. Both AFB1-oxide and AFB1-Cl2 react with guanines in double-stranded DNA to induce similar sequence-specific, alkali-labile sites. Reactivity with partial DNA duplexes as well as the use of single-strand specific chemical probes directly demonstrates that AFB1-Cl2, like AFB1-oxide, prefers base-paired guanines over non-base-paired guanines. DNA replication block patterns induced by AFB1-oxide are essentially similar to those induced by AFB1-Cl2. Unexpectedly, and unlike other tested DNA lesions, Mn2+ does not appear to affect the template blocking properties of the adduct formed by AFB1-Cl2 or AFB1-oxide. The sites for replication stoppage as well as the lack of a Mn2+ effect on adducted templates have implications for the mechanisms of mutagenesis by activated AFB1.     

Water stress enhances expression of an alpha-amylase gene in barley leaves

The amylases of the second leaves of barley seedlings (Hordeum vulgare L. cv Betzes) were resolved into eight isozymes by isoelectric focusing, seven of which were β-amylase and the other, α-amylase. The α-amylase had the same isoelectric point as one of the gibberellin-induced α-amylase isozymes in the aleurone layer. This and other enzyme characteristics indicated that the leaf isozyme corresponded to the type A aleurone α-amylase (low pI group). Crossing experiments indicated that leaf and type A aleurone isozymes resulted from expression of the same genes.

In unwatered seedlings, leaf α-amylase increased as leaf water potential decreased and ABA increased. Water stress had no effect on β-amylase. α-Amylase occurred uniformly along the length of the leaf but β-amylase was concentrated in the basal half of the leaf. Cell fractionation studies indicated that none of the leaf α-amylase occurred inside chloroplasts.

Leaf radiolabeling experiments followed by extraction of α-amylase by affinity chromatography and immunoprecipitation showed that increase of α-amylase activity involved synthesis of the enzyme. However, water stress caused no major change in total protein synthesis. Hybridization of a radiolabeled α-amylase-related cDNA clone to size fractionated RNA showed that water-stressed leaves contained much more α-amylase mRNA than unstressed plants. The results of these and other studies indicate that regulation of gene expression may be a component in water-stress induced metabolic changes.

     

Taxonomy, variation, and relationships in the Hordeum parodii group (Poaceae)

The Hordeum parodii group contains three species, viz. H. parodii Covas (6x), H. tetraploidum Covas (4x), and H. fuegianum Bothmer, Jacobsen, et Jørgensen, sp. nov. (4x). The former two species mainly occur in C and S Argentina, while H. fuegianum is native to Tierra del Fuego. All three species are probably of alloploid origin. Morphological, isoenzyme variation and cytogenetic data are presented.     

Na+-H+ exchange in luminal-membrane vesicles from rabbit proximal convoluted and straight tubules in response to metabolic acidosis.

Na+-H+-exchanger activity of pars convoluta and pars recta luminal-membrane vesicles prepared from the proximal tubule of acidotic and control rabbits were assayed by a rapid-filtration technique and an Acridine Orange method. Both experimental approaches revealed the existence of an antiporter, sensitive to metabolic acidosis, in pars convoluta membrane vesicles. Kinetic data, obtained with the pH-sensitive dye, showed that the Km for Na+ transport was unchanged by acidosis, whereas Vmax. for exchanger activity was increased, on an average, by 44%. The fluorescence method, in contrast with the rapid-filtration technique, was able to detect exchanger activity in pars recta membrane vesicles. The Km value for the antiporter located in pars recta is comparable with that calculated for pars convoluta membrane vesicles. By contrast, the Vmax. of this exchanger is only about 25% of that found for pars convoluta. Furthermore, metabolic acidosis apparently does not increase Na+-H+-exchanger activity of pars recta luminal-membrane vesicles.     

The metabolism of 3-deazaguanine and 3-deazaguanosine by human cells in culture

The metabolism of the purine analogs 3-deazaguanine and 3-deazaguanosine was studied in cultured human cells using radiolabeled tracers, individual enzyme assays, and mutant cell lines. The toxicity of each drug appeared to require conversion to the 5' nucleotide. The base was converted to the nucleotide by hypoxanthine guanine phosphoribosyl transferase. The conversion of the nucleoside to the nucleotide was catalyzed by an unidentified kinase. Purine nucleoside 3-deazaguanosine-5'-monophosphate was converted to its corresponding di- and triphosphate by guanylate kinase. Both the base and the nucleoside were incorporated into DNA but not RNA.     

Selective measurement of starch synthesizing enzymes in permeabilized potato tuber slices

Osmotically permeabilized potato (Solanum tuberosum L.) tuber slices were used to study the biosynthesis of starch under semi in vivo conditions. Criteria to distinguish the various enzymes involved in starch biosynthesis were developed based on the characteristics of the enzymes in in vitro experiments. Branching enzyme activity was inhibited at pH 8.5 or higher, while the starch synthases functioned optimally between pH 8.8 and 9.1. Unprimed soluble starch synthase activity was only apparent in the presence of sodium citrate (0.4 molar or higher). Granulebound and primed soluble starch synthase were active in the absence of sodium citrate. Primed soluble starch synthase activity was susceptible to inhibition by 10 millimolar zinc sulfate, while granule-bound starch synthase activity was not. The incorporation of the Glc moiety of ADP-Glc into starch in tissue slices by the various starch synthases was consistent with in vitro data with respect to the affinity of the enzymes for substrate, the pH profile, the stimulation by citrate, and the inhibition by zinc sulfate. These data were used to determine the activity of each of the starch synthases in tissue slices: granule-bound and soluble starch synthase transferred 37 and 55 picomoles ADP-Glc per hour per milligram fresh weight into starch of permeabilized tissue slices at 30°C and pH 9.1. In the presence of 0.5 molar sodium citrate, at least 40 picomoles ADP-Glc per hour per milligram fresh weight as transferred into starch by unprimed soluble starch synthase activity.     

Growth dynamics in the American alligator (Alligator mississippiensis)

The growth dynamics of the American alligator ( Alligator mississippiensis ) were studied in the subtropical Florida Everglades using extensive mark-recapture data from over 2000 recaptures of known-aged and unknown-aged animals. A model based on the power curve best describes growth of Everglades alligators. The nonasymptotic character of this curve leads to rejection of the hypothesis that alligator growth is determinate. A model consisting of piece-wise linear equations better described growth in the first year, and suggested a period of arrested growth occurred in the first winter. A comparison of predictions from growth models derived from several populations indicated that Everglades alligators grew more slowly than did those in more temperate areas, leading to the rejection of the hypothesis that growth rates in subtropical Florida would be elevated because of the long growing season. We attribute this result to a combination of increased maintenance costs and a limited resource base in the Everglades.
Analyses considered the extent to which growth model evaluation and use can be affected by data selection. Mathematical constraints posed by negative growth data can be alleviated by including growth records over combined recapture intervals to achieve a positive growth increment. However, periods of no to negative growth may be real, and such deviations are obscured by fitting growth data to monotonically increasing models.