Artificial destratification of a small tropical reservoir: effects upon the phytoplankton

Seasonal changes in the phytoplankton community of a small tropical reservoir were monitored over a four year period comprising of an initial two seasonal cycles during which the water column stratified strongly for extended periods each year, and two further seasonal cycles after installation of a mechanical aeration system to induce artificial destratification. In the unmanaged reservoir, the concentration of chlorophyll a at 0.5 m reached maximum values (on one occasion > 90 mg m⁻³) when the water column was stratified and the epilimnion was very shallow (ca 2 m depth). The hypolimnion at this time was anoxic (less than 2% oxygen saturation) and had a high concentration of bacteriochlorophyll (100–200 mg m⁻³). The phytoplankton community of the unmanaged reservoir was generally dominated by cyanobacteria (Cylindrospermopsis raciborskii, Anabaena tenericaulis) during the warmer months of the year (November–March) (but replaced by chlorophyta, dinophyceae and euglenophyceae after periods of intense rain) and by bacillariophyceae (Synedra ulna var. chaseana, S. tenera) during the cooler, dry months. In the artificially destratified reservoir (8 h aeration day⁻¹), the phytoplankton community was largely dominated by diatoms except after depletion of the silica content of the water column which caused diatoms to be replaced by cyanobacteria (dominated by A. tenericaulis) and a range of chlorophytes. The changing pattern of stratification and circulation of the water column in the unmanaged reservoir caused repeated disruption of the established phytoplankton assemblage with peaks of high biomass associated with transient cyanobacterial blooms. Continuous aeration and the consequent increase in the ratio mixed: euphotic depth provided conditions suitable for dominance of the phytoplankton by diatoms, as long as silica was available, and resulted in average chlorophyll levels higher than in the unmanaged reservoir (120 ± 10 v. 64 ± 9 mg m⁻²). Hierarchical fusion analysis based on the biomass of species differentiated the phytoplankton samples into cluster groups that could be related primarily to stratification or mixing of the water column.     

An extensive review on antifungal approaches in the treatment of mucormycosis

During the period of COVID-19, the occurrences of mucormycosis in immunocompromised patients have increased significantly. Mucormycosis (black fungus) is a rare and rapidly progressing fungal infection associated with high mortality and morbidity in India as well as globally. The causative agents for this infection are collectively called mucoromycetes which are the members of the order Mucorales. The diagnosis of the infection needs to be performed as soon as the occurrence of clinical symptoms which differs with types of Mucorales infection. Imaging techniques magnetic resonance imaging or computed tomography scan, culture testing, and microscopy are the approaches for the diagnosis. After the diagnosis of the infection is confirmed, rapid action is needed for the treatment in the form of antifungal therapy or surgery depending upon the severity of the infection. Delaying in treatment declines the chances of survival. In antifungal therapy, there are two approaches first-line therapy (monotherapy) and combination therapy. Amphotericin B ( 1 ) and isavuconazole ( 2 ) are the drugs of choice for first-line therapy in the treatment of mucormycosis. Salvage therapy with posaconazole ( 3 ) and deferasirox ( 4 ) is another approach for patients who are not responsible for any other therapy. Adjunctive therapy is also used in the treatment of mucormycosis along with first-line therapy, which involves hyperbaric oxygen and cytokine therapy. There are some drugs like VT-1161 ( 5 ) and APX001A ( 6 ), Colistin, SCH 42427, and PC1244 that are under clinical trials. Despite all these approaches, none can be 100% successful in giving results. Therefore, new medications with favorable or little side effects are required for the treatment of mucormycosis.     

Sites of iodination in recombinant human brain-derived neurotrophic factor and its effect on neurotrophic activity.

Recombinant human brain-derived neurotrophic factor (BDNF) is now under extensive investigation because of its potential clinical applications. Radioactively labeled proteins are usually required to study receptor binding and pharmacokinetic properties of proteins. This study was undertaken to see if iodination affects the biological and conformational properties of a recombinant BDNF. BDNF was iodinated using a stoichiometric amount of nonradioactive cold NaI to minimize multiple iodinations. Of the four tyrosines present in BDNF--Tyr-52, Tyr-54, Tyr-63, and Tyr-86--only Tyr-63 and Tyr-86 were iodinated under the experimental conditions used. Iodination of Tyr-63 resulted in modification without alteration of the biological activity, whereas iodination of Tyr-86 resulted in a molecule with highly compromised biological activity. Similar inactivation was observed if both Tyr-63 and Tyr-86 were iodinated. These modified proteins exhibited conformation and dimerization apparently identical to those of the native protein, as demonstrated by analytical ultracentrifugation, gel filtration, light scattering, and circular dichroism. From these results, we concluded that Tyr-52 and Tyr-54 are not accessible to the reagent and are probably buried in the hydrophobic core, whereas Tyr-63 and Tyr-86 are exposed on the surface of the molecule; of the two exposed residues, only Tyr-86 contributes to the biological activity.     

The interaction of the steroidal antagonist faslodex and methotrexate.

Faslodex (FAS, ICI 182, 780), a novel steroidal estrogen antagonist decreased high-dose methotrexate (MTX) cytotoxicity in MCF-7 breast cancer cells. When FAS is given at least 24 hr prior to MTX, the resultant interaction is antagonistic. However, when breast cancer cells are exposed to FAS 24 hr after MTX, the interaction between FAS and MTX is not antagonistic. The proliferation of cells exposed to 0.1 microM FAS and 10 microM MTX alone or in combination with FAS 24 hr prior to MTX was in the following order: FAS>FAS 24 hr prior to MTX>MTX. MTX administration 24 hr prior to FAS had the following inhibitory effects on the growth of cells: MTX 24 hr prior to FAS >MTX>FAS 24 hr prior to MTX>FAS>control (no drug exposure). To determine if the antagonistic interaction between FAS and MTX was a function of sequence and time, cells were exposed to FAS 24 hr and 36 hr prior to MTX exposure. The percentages of control rates were 42.70 +/- 4.60% and 57.89 +/- 0.55%, respectively, from a 24 hr and 36 hr exposure of FAS prior to MTX. The growth rates after 24 and 36 hr exposures to MTX alone were 30.30 +/- 0.61% and 33.11 +/- 2.57% of control rates, respectively. These studies suggest that: a) the interactions between FAS and MTX are sequence-dependent; b) FAS antagonizes the effect of MTX when FAS administration precedes MTX, and c) FAS antagonism to MTX is a function of time.     

Role of exercise testing early after myocardial infarction in identifying candidates for coronary surgery.

It has been suggested that ST depression in lead V5 or equivalent on early exercise testing after acute myocardial infarction predicts a high risk of death. To evaluate exercise testing and radionuclide ventriculography in this context 103 consecutive patients with myocardial infarction who were able to undertake a limited exercise test before discharge from hospital were exercised and underwent gated blood pool scanning. No serious complications resulted from exercise testing. Twenty nine patients developed ST depression in lead V5, 19 had exertional hypotension, 31 developed a heart rate of greater than or equal to 130 beats/min, and 15 had complex ventricular arrhythmias. Death during the first year after discharge from hospital was associated with exertional hypotension (p less than 0.001) and a heart rate on exercise testing of greater than or equal to 130 beats/min (p less than 0.05); these two variables identified all nine deaths. Inability to complete the exercise protocol for any reason was also predictive of death (p less than 0.01). Ventricular arrhythmias and ST depression in lead V5 induced by exercise were not significantly associated with an increased risk of death. The mean (SD) radionuclide ejection fraction in the patients who died was 29 (16%) compared with 43 (11)% in the patients who survived (p less than 0.001). ST changes on exercise testing after myocardial infarction appear to be less predictive of later complications than haemodynamic signs, which may indicate left ventricular damage rather than ischaemia.     

Kinetics of the renaturation of yeast tRNA3 leu.

Yeast tRNA₃^Leu is one of several tRNA molecules which can adopt a stable, biologically inactive, denatured conformation. The circular dichroism of the native and denatured conformers differs, providing the basis for the present study of the mechanism for the renaturation process. Conversion of the denatured structure to the native takes place in two steps: a rapid change occurring immediately on addition of Mg⁺⁺, followed by a slower, strongly temperature-dependent step which returns the molecule to its biologically active state. Optimal kinetic data for the second step could be obtained at 285 nm. Analysis of the time dependence of Δε₂₈₅ by the Guggenheim method demonstrated that this step follows first-order kinetics. The temperature dependence of the rate constants over the range 32–41°C yielded the following parameters for the rate-limiting step: E_a = 69 kcal/mole, ΔH^? = 69 kcal/mole, and ΔS^? = 146 cal/mole deg. Values of this magnitude are typical of order—order transitions in nucleic acids.