Ammonium photo-production by heterocytous cyanobacteria: potentials and constraints

Over the last decades, production of microalgae and cyanobacteria has been developed for several applications, including novel foods, cosmetic ingredients and more recently biofuel. The sustainability of these promising developments can be hindered by some constraints, such as water and nutrient footprints. This review surveys data on N₂-fixing cyanobacteria for biomass production and ways to induce and improve the excretion of ammonium within cultures under aerobic conditions. The nitrogenase complex is oxygen sensitive. Nevertheless, nitrogen fixation occurs under oxic conditions due to cyanobacteria-specific characteristics. For instance, in some cyanobacteria, the vegetative cell differentiation in heterocyts provides a well-adapted anaerobic microenvironment for nitrogenase protection. Therefore, cell cultures of oxygenic cyanobacteria have been grown in laboratory and pilot photobioreactors (Dasgupta et al., 2010; Fontes et al., 1987; Moreno et al., 2003; Nayak & Das, 2013). Biomass production under diazotrophic conditions has been shown to be controlled by environmental factors such as light intensity, temperature, aeration rate, and inorganic carbon concentration, also, more specifically, by the concentration of dissolved oxygen in the culture medium. Currently, there is little information regarding the production of extracellular ammonium by heterocytous cyanobacteria. This review compares the available data on maximum ammonium concentrations and analyses the specific rate production in cultures grown as free or immobilized filamentous cyanobacteria. Extracellular production of ammonium could be coupled, as suggested by recent research on non-diazotrophic cyanobacteria, to that of other high value metabolites. There is little information available regarding the possibility for using diazotrophic cyanobacteria as cellular factories may be in regard of the constraints due to nitrogen fixation.     

A Financial Market Model Incorporating Herd Behaviour

Herd behaviour in financial markets is a recurring phenomenon that exacerbates asset price volatility, and is considered a possible contributor to market fragility. While numerous studies investigate herd behaviour in financial markets, it is often considered without reference to the pricing of financial instruments or other market dynamics. Here, a trader interaction model based upon informational cascades in the presence of information thresholds is used to construct a new model of asset price returns that allows for both quiescent and herd-like regimes. Agent interaction is modelled using a stochastic pulse-coupled network, parametrised by information thresholds and a network coupling probability. Agents may possess either one or two information thresholds that, in each case, determine the number of distinct states an agent may occupy before trading takes place. In the case where agents possess two thresholds (labelled as the finite state-space model, corresponding to agents’ accumulating information over a bounded state-space), and where coupling strength is maximal, an asymptotic expression for the cascade-size probability is derived and shown to follow a power law when a critical value of network coupling probability is attained. For a range of model parameters, a mixture of negative binomial distributions is used to approximate the cascade-size distribution. This approximation is subsequently used to express the volatility of model price returns in terms of the model parameter which controls the network coupling probability. In the case where agents possess a single pulse-coupling threshold (labelled as the semi-infinite state-space model corresponding to agents’ accumulating information over an unbounded state-space), numerical evidence is presented that demonstrates volatility clustering and long-memory patterns in the volatility of asset returns. Finally, output from the model is compared to both the distribution of historical stock returns and the market price of an equity index option.     

Stability and degradation of mRNA

Differential mRNA stability plays an important role in the regulation of gene expression. Several recent advances have helped to define the general pathways by which mRNA is degraded in prokaryotic cells, although many details remain to be elucidated. Much less is known about the pathways of degradation in eukaryotic cells, but recent studies on specific systems have highlighted both differences from and similarities to prokaryotic pathways.     

Isolation and characterization of eight compound microsatellite markers in a mangrove tree Kandelia candel (L.) Druce

Kandelia candel is an important mangrove tree species of family Rhizophoraceae. Here we isolated eight codominant compound microsatellite simple sequence repeat (SSR) loci from K. candel. Our isolated loci provided compound SSR markers with polymorphism of three to 11 alleles per locus. The expected and observed heterozygosities ranged from 0.230 to 0.887 and from 0.083 to 1.00, respectively. These markers would be the useful tools for analysing questions concerning population genetic structure and mating system of K. candel.     

Significance of mirex-caused hypoglycemia and hyperlipidemia in rats

Treatment of rats with mirex (40 ppm in diet) caused hypoglycemia, liver enlargement, and inhibition of adrenal corticosteroid-synthesizing enzyme activity. At toxic dosages (20,000 ppm mirex in diet, which has a lethal toxicity-50 [LT-50] of ten days) poisoned female rats showed severe hypoglycemia, fatty liver, adrenal hyperplasia, hypophagia, lipid mobilization, and body weight (bw) loss. A 50 μg/kg intraperitoneal (IP) dose of 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) in male rats caused similar effects two days posttreatment. Hypoglycemia could be overcome by prednisone (which also inhibited adrenocorticoid-synthesizing enzyme activities) but not by streptozotocin treatment, indicating that hypoglycemia may be related to glucocorticoid deficiency resulting from inhibition of their synthesis and not by direct effects on pancreatic β-cells. Glucocorticoid deficiency could also cause increased release of adrenocorticoid hormone (ACTH), which may enhance fat mobilization caused by hypophagia.     

Intermediate sucrose octa-acetate sensitivity suggests a third allele at mouse bitter taste locus Soa and Soa-Rua identity

Mice have been characterized as either tasters or non-tastersof the bitter compound sucrose octa-acetate(SOA). However, 11of 17 supposedly non-taster inbred strains were found to avoid1 mM SOA. All 17 strains were indifferent to 0.1 mM SOA. Tasterstrains avoided both concentrations. The intermediate phenotypewas dubbed demitaster. A consistent phenotypic dominance orderwas found in crosses among both inbred and outbred strains (taster> non-taster > demitaster). Demitasters were found (withtasters) in an outbred strain showing monogenic segregationfor SOA avoidance. This, plus monogenic segregation in a back-crossof taster to demitaster inbred strains, suggested a third alleleat the Soa locus (Soa^c). Demitaster allelism was supported bythe strong associations found in 15 strains between the threeSOA phenotypes and HindIII restriction fragment patterns forthe closely linked Prp (proline rich protein) loci. SOA demitasterstrains were also intermediate in raffinose undeca-acetate (RUA)avoidance. Furthermore, B6.SW-Soa² congenic mice avoided notonly SOA, but RUA and eight other acetylated sugars. A previouslyproposed separate RUA-sensitivity gene (Rua) thus appeared tobe redundant.     

Alkylphenol hydroxylases in the oxidation of p-cresol, 4-ethylphenol and 4-n-propylphenol by Pseudomonas putida JD1

Abstract Growth of Pseudomonas putida JD1 on 4-ethylphenol results in the production of the flavocytochrome c, 4-ethylphenol methylenehydroxylase. Both p -cresol and 4- n -propylphenol are substrates for this enzyme. 4-Ethylphenol methylenehydroxylase is also produced by the organism when grown with 4- n -propylphenol. However, when grown with p -cresol, a different hydroxylase is produced which shows greater activity towards p -cresol than towards 4-ethylphenol, and is not active towards 4- n -propylphenol.     

Hormone-dependent processing of the avian progesterone receptor

Avian progesterone receptor exists as two forms, A and B, with molecular weights of 79,000 and 110,000 daltons, respectively. The origin and significance of these two forms is an area of active investigation and debate. Monoclonal antibodies produced against these two forms were used to examine receptor stability in cytosol and changes in the receptor forms induced by hormone binding. The lability of hormone binding at elevated temperatures is well documented. Analysis by Western blotting showed the receptor was stable in freshly prepared oviduct cytosol for 2 hr at 37°C, while hormone binding was lost within 30 min. However, loss of receptor through degradation was seen when cytosol was prepared from frozen tissue or when homogenization was excessive. Progesterone was injected into diethylstilbestrol-stimulated chicks to examine, in vivo, effects of hormone treatment on receptor forms in the cytosol and nuclear fractions. Progesterone treatment caused a time- and dose-dependent conversion of the A receptor to a form (A′) with a slower electrophoretic mobility. The cytosolic progesterone receptor was divided equally between the B and A forms, while the nuclear receptor was predominantly A′. The amount of nuclear receptor was consistently less than cytosolic receptor. Receptor phosphorylation was analyzed by incubating tissue minces with [³²P]orthophosphate with or without progesterone followed by immune isolation of receptor forms. Progesterone treatment caused a time-dependent increase in cytosol receptor phosphorylation which was evident after 5 min of treatment. This phosphorylation was observed with both the A and B receptor forms. The results indicate that receptor phosphorylation is a very early event during progesterone action.