Understanding the true burden of “Naegleria fowleri” (Vahlkampfiidae) in patients from Northern states of India: Source tracking and significance

The present study is an attempt to investigate the presence of Naegleria fowleri in Indian population. A total of 307 patients were enrolled and water samples were collected from both residential and surrounding areas of patients found positive for N. fowleri. The different species of Naegleria from both clinical and water samples were identified taxonomically. Recommended microbiological conventional techniques were used to identify different Naegleria stages and other free-living amoebae from the samples. PCR assays, using both genus and species specific primers were also optimized. None of the samples were positive by conventional microbiological examinations. However, PCR assays detected only three samples positive for N. fowleri. A total of 10 water bodies (ponds), that were used by Naegleria positive patients were examined. The pH and temperature of the water samples collected from water bodies ranged between 5.6–7.2 and 25–32 °C respectively. Among all the 10 water samples tested, four samples were positive for genus Naegleria by PCR assay, of which only two samples, showed positive amplification for N. fowleri. The sequence analysis of N. fowleri strain belonged to genotype II.     

Confronting the challenges of discovery of novel antibacterial agents

Bacterial resistance is inevitable and is a growing concern. It can be addressed only by discovery and development of new agents. However the discovery and development of new antibacterial agents are at an all time low. This article broadly examines the historical as well as current status of antibacterial discovery and provides some perspective as how to address some of the challenges.     

Isolation and characterization of a type II restriction endonuclease from Streptococcus thermophilus

The alpha-toxin (phospholipase C) of Clostridium perfringens has been reported to contain catalytically essential zinc ions. We report here that histidine residues are essential for the co-ordination of these ion(s). Incubation of alpha toxin with diethylpyrocarbonate, a histidine modifying reagent, did not result in the loss of phospholipase C activity unless the protein was first incubated with EDTA, suggesting that zinc ions normally protect the susceptible histidine residues. When the amino acid sequences of three phospholipase C's were aligned, essential zinc binding histidine residues in the non-toxic B. cereus phospholipase C were found in similar positions in the toxic C. perfringens enzyme and the weakly toxic C. bifermentans phospholipase C.     

Mediator structure and conformation change

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Studies on the protolytic reactions coupled with water cleavage in photosystem II membrane fragments from spinach

The protolytic reactions of PSII membrane fragments were analyzed by measurements of absorption changes of the water soluble indicator dye bromocresol purple induced by a train of 10 s flashes in dark-adapted samples. It was found that: a) in the first flash a rapid H⁺-release takes place followed by a slower H⁺-uptake. The deprotonation is insensitive to DCMU but is completely eliminated by linolenic acid treatment of the samples; b) the extent of the H⁺-uptake in the first flash depends on the redox potential of the suspension. In this time domain no H⁺-uptake is observed in the subsequent flashes; c) the extent of the H⁺-release as a function of the flash number in the sequence exhibits a characteristic oscillation pattern. Multiphasic release kinetics are observed. The oscillation pattern can be satisfactorily described by a 1, 0, 1, 2 stoichiometry for the redox transitions S_i S_i+1 (i=0, 1, 2, 3) in the water oxidizing enzyme system Y. The H⁺-uptake after the first flash is assumed to be a consequence of the very fast reduction of oxidized Q₄₀₀(Fe³⁺) formed due to dark incubation with K₃[Fe(CN)₆]. The possible participation of component Z in the deprotonation reactions at the PSII donor side is discussed.Abbreviations A protonizable group at the PSII acceptor side - BCP Bromocresol Purple - DCMU 3-(3,4-dichlorophenyl)-1,1-dimethylurea - FWHM Full Width at Half Maximum - Q_A, Q_B primary and secondary plastoquinone at PSII acceptor side - Q₄₀₀ redox group at PSII-acceptor side (high spin Fe²⁺) - P680 Photoactive chlorophyll of PSII reaction center - S_i redox states of the catalytic site of water oxidation - Z redox component connecting the catalytic site of water oxidation with the reaction center     

The effect of the dark interval in intermittent light on thylakoid development: photosynthetic unit formation and light harvesting protein accumulation

Etiolated bean plants were grown in intermittent light with dark intervals of shorter or longer duration, to modulate the rate of chlorophyll accumulation, relative to that of the other thylakoid components formed. We thus produced conditions under which chlorophyll becomes more or less a limiting factor. We then tested whether LHC complexes can be incorporated in the thylakoid. It was found that an equal amount of chlorophyll, formed under the same total irradiation received, may be used for the stabilization of few and large-in-size PS units containing LHC components (short dark-interval intermittent light), or for the stabilization of many and small-in-size PS units with no LHC components (long dark-interval intermittent light). The size of the PS units diminishes as the dark-interval duration is increased, with no further change after 98 minutes. The PSII/cytf ratio remains constant throughout development in intermittent light and equal to that of mature chloroplasts (PSII/cytf = 1) except in the case of very long dark-interval regimes, where about half PSII units per cytf are present. The PSII/PSI ratio was found to be correlated with the PSII unit size (the larger the size, the lower the ratio). The number of PSI units operating on the same electron transfer chain varied depending on the size of the PSII unit (the larger the PSII unit size, the more the PSI units per chain). The results suggest that it is not the chlorophyll content per se which regulates the stabilization of LHC in developing thylakoids and consequently the size of the PS units, but rather the rate by which it is accumulated, relative to that of the other thylakoid components.Abbreviations Chl Chlorophyll - CL Continuous light - CPa the reaction center complex of PSII - CPI the reaction center complex of PSI - CPIa Chlorophyll protein complex containing the CPI and the light harvesting complex of PSI - fr w fresh weight - LDC Light dark cycles - LHC-I Light-harvesting complex of PSI - LHC-II Light harvesting complex of PSII - PS photosystem - PSI photosystem I - PSII photosystem II     

Pheophytin-mediated energy storage of photosystem II particles detected by photoacoustic spectroscopy

The photoacoustic (PA) characteristics (energy storage and heat dissipation) of photosystem II (PSII) core-enriched particles from barley were studied (i) in conditions where there was electron flow, i.e., in the presence of a combination of the electron acceptor K₃ Fe (CN)₆, referred to as FeCN, and the electron donor diphenylcarbazide (DPC), and (ii) in conditions where electron flow was suppressed, i.e., in the absence of FeCN and DPC. The experimental data show that a decrease of heat dissipation with a minimum at 540 nm can be interpreted as energy storage resulting from the presence of pheophytin (Pheo) in the PSII particles. On account of the capability of the PA method to measure the energy absorbed by the chromophores which is converted to heat, it is suggested that the PA detection of Pheo present in the PSII complex will permit to clarify the function of processes involving non-radiative relaxation of excited states in P680-Pheo-Q_A interactions.Abbreviations -Car -Carotene - Chl Chlorophyll - DPC Diphenylcarbazide - EPR Electron Paramagnetic Resonance - FeCN potassium ferricyanide - HEPES N-2-hydroxyethylenepiperazine-N-2-ethanesulfonate - P680 reaction center of PSII - PA Photoacoustic - Pheo pheophytin - PSI photosystem I - PSII photosystem II - Q_A primary electron acceptor of PSII     

Is functional manganese involved in hydrogen-peroxide-stimulated anomalous oxygen evolution in CACl2-washed photosystem II membranes?

When detergent-derived photosystem II (PSII) membranes are treated with CaCl₂ to remove the three extrinsic proteins associated with the O₂-evolving complex, the resulting membranes (CaPSII) can still catalyze water oxidation if sufficient Ca²⁺ and Cl^- are present. When CaPSII membranes are exposed to single turnover flashes on an O₂ rate electrode, anomalous O₂ is produced by the first two flashes. The addition of catalase to the membrane suspension completely inhibits O₂ produced by the first two flashes, but not by subsequent flashes. Exogenous H₂O₂ stimulates anomalous O₂ production by the first few flashes in CaPSII membranes, but not in control PSII membranes. Diuron (DCMU) does not inhibit H₂O₂-stimulated O₂ production by the first flash. However, it does inhibit the O₂ yield of all subsequent flashes, indicating that all flash-induced O₂ signals in CaPSII membranes are dependent on photosystem II electron transport. H₂O₂ stimulation of O₂ yields is inhibited in Tris-, heat-, and EDTA-(ethylenediaminetetraacetic acid)-treated CaPSII. In the presence of high salt, H₂O₂ (but not EDTA) treatment of CaPSII, extracts Mn functional in normal photosynthetic O₂ evolution. The addition of exogenous Mn²⁺ reconstitutes anomalous O₂ production in Tris-and H₂O₂/EDTA-treated CaPSII preparations but only in the presence of H₂O₂. Anomalous H₂O₂-stimulated O₂ production can be observed both with a Clark electrode (steady state) and an O₂ rate electrode (flash sequence). The mechanism involves electron donation from H₂O₂, mediated by free Mn²⁺, to PSII, and the 33-kDa extrinsic protein under some conditions can block this process. Since H₂O₂ can remove functional Mn from CaPSII membranes, its presence can convert functional Mn to the Mn²⁺ mediator state required for anomalous O₂ production. EDTA binds Mn in CaPSII disrupted by H₂O₂ and prevents anomalous O₂ evolution.Abbreviations CaPSII a PSII preparation washed with approximately 1M CaCl₂ - Chl chlorophyll - DCBQ 2,6-dichloro-p-benzoquinone - DCMU (diuron) 3-(3,4-dichlorophenyl)-1,1-dimethylurea - EDTA ethylenediaminetetraacetic acid - MES 2-[N-morpholino]-ethanesulfonic acid - PSII a detergent-derived photosystem II membrane preparation - RC reaction center - Tris tris(hydroxymethyl)-aminomethane - Y_n oxygen rate electrode flash yield resulting from the nth flash of a sequence of single turnover flashes of light Operated by the Midwest Research Institute for the U.S. Department of Energy under contract DE-AC02-83CH10093.     

Metabolism and excretion of acetylchromenes by the migratory grasshopper

The extent of metabolism and excretion of three acetylchromenes (two toxic, one relatively nontoxic) were examined in adult migratory grasshoppers (Melanoplus sanguinipes) following topical administration. Both the total amount excreted (parent plus metabolites) and the proportion of parent compound in the excreta were inversely correlated with contact toxicity. Both toxic and nontoxic acetylchromenes are rapidly absorbed from the cuticle, with maximum excretion of parent and metabolite chromenes from 4 to 8 h posttreatment in each case. Much of the applied compounds (60–80%) apparently remains within the insect, and cannot be recovered by extraction of the insect. Metabolites formed result from simple oxidative and reductive transformations. For all of the compounds tested (including the allatocidin precocene II), the major mode of metabolism results from aliphatic hydroxylation of one of the geminal methyl groups on the chromene. No conjugated metabolites were found in the excreta.