Chromosome profile ofLeishmania donovani: Interstrain and interspecific variations

The genome ofLeishmania donovani AG83, a virulent strain causing kala-azar, was resolved into 29 chromosomal bands by pulsed field gel electrophoresis (pFGE) under standardized conditions. Comparison of the karyotype with those of other strains and species revealed variations. By Southern hybridization, specific genes were localized to individual chromosomes. Twenty-two copies ofβ-tubulin genes are located on band 27 (1.63 Mb); minor copies are present in band 16 (850 kb) and band 9 (650 kb). Aβ-tubulin related nontranscribed locus was isolated from a genomic library and shown to contain repetitive sequences hybridizing throughout the genome. Single chromosomes contain multicopy clusters of gp63 and rnini-exon-derived RNA genes, but interspecific variations were observed in each case. The results emphasize the importance of using a standard reference strain ofLeishmania donovani for coordinated genome mapping of this clinically important organism.     

A further fractionation of agarose

Hydrobiologia - Commercial agarose can be separated into two components by fractional precipitation using alcohols or glycols. The less soluble component has a much higher gel strength and lower...     

A simple tool for calculating egg shape,volume and surface area from digital images

The geometrical properties of eggs – such as volume and surface area – have uses ranging from ecological, physiological and morphological studies in birds, to predictions of chick condition in the poultry industry. Although measurements of an egg's length and breadth can be used to approximate its geometry, the coefficients used in these models are specific to the original test population, and intraspecific variation in egg shape means these methods cannot be used reliably beyond that population. Here I present a novel mathematical formula to describe the curvature of a bird's egg that can be used to calculate the shape, volume and surface area of an egg precisely from digital images. Using data from several species I demonstrate that the model has a greater level of accuracy than length‐ and breadth‐based methods, and release the user‐friendly tool for others to use for measuring eggs from digital images.     

Magnetic field-induced increase of the yield of (bacterio)chlorophyll emission of some photosynthetic bacteria and of Chlorella vulgaris

In photosynthetic bacteria, in which the iron-ubiquinone complex X is prereduced, a magnetic field induces an increase of the emission yield, which is correlated with the decrease in reaction center triplet yield reported previously (Hoff, A.J., Rademaker, H., van Grondelle, R. and Duysens, L.N.M. (1977) Biochim. Biophys. Acta 460, 547–554). Our results support the hypothesis that under these conditions charge recombination of the oxidized primary donor and the reduced primary acceptor predominantly generates the excited singlet state of the reaction center bacteriochlorophyll.In Chlorella vulgaris and spinach chloroplasts, at 120 K, the magnetic field has an effect similar to that found in bacteria, which suggests that an intermediary electron acceptor between P-680 and Q is present in Photosystem II also.     

Four decades of old field vegetation development and the role of Celastrus orbiculatus in the northeastern United States

Abstract. This paper describes four decades of in situ vegetation change in a post-agricultural site in southern New England where the role of the introduced vine, Celastrus orbiculatus, has drastically modified the course of vegetation development. An initial perennial forb-grassland community was replaced by two strikingly different physiognomic vegetation types-an early hardwood forest and a vine community occupying the same site 40 yr later. This ecological phenomenon was unpredictable since Celastrus was not recorded at the site until the 1970s. Within the young hardwood forest dominated by Prunus serotina and Acer rubrum, a few old field species (five) persist, whereas 17 forest herbs have become established. Typical forest shrubs are rare or absent. The Celastrus-dominated vine community has suppressed or eliminated pre-existing growth to form a relatively stable community where a forest vegetation is the regional vegetation type. Celastrus also appears to be facilitating a native vine (Vitis labrusca) by forming a ‘ladder’ for its advance. Although A. rubrum and Quercus spp. could ultimately dominate the forest community, the contiguous and aggressive nature of Celastrus makes predictions questionable. This long-term study highlights the unpredictable nature of old field succession and the role of an exotic species in threatening the natural vegetation development.     

Application of a pulsed electric field to cross-flow ultrafiltration of protein solution

The application of pulsed electric field was investigated in the crossflow ultrafiltration of BSA (bovine serum albumn) to economize the application time of electric current as well as to avoid inherent problems of long-term application of electric field. During the application of various cyclic patterns of pulsed electric current, the averaged filtration flowrate and the degree of concentration were maintained higher than those obtained in the absence of electric current application. The temperature increase, pH change, and BSA loss by electrodeposition were all negligible during the operation. The averaged filtration flowrate increased as the ON/OFF duration ratio of electric current was higher and as the period of ON/OFF cycle was shorter. The re-establishment of concentration polarization was dependent to the duration of current OFF state and, therefore, a longer duration of OFF state was not favorable in maintaining higher filtration flow rate. Although the averaged filtration flowrate was enhanced as the magnitude of electric current increased, the flowrate enhancement became smaller as the magnitude of current increased because there exists a current value above which the degree of electrokinetic depolarization is no further improved.     

On the structure of bacteriochlorophyll molecular aggregates in the chlorosomes of green bacteria. A molecular modelling study

The supramolecular structure of methyl (3¹ R)-BChlided aggregation has been explored by molecular modelling in order to elucidate the unusual structure of the BChl rods in the chlorosomal antennae of green bacteria. The aggregate construction progressed from a BChlide monomer in 5c coordination which was stepwise combined to form trimeric, pentameric and decameric chlorin stacks, all incorporating Mg····O-H as a basic interaction element which links two chlorins between the 3¹-hydroxyl oxygen and the Mg. Up to the level of the trimer, the structures were optimized by both a semiempirical quantum chemical method (PM3) and a force field method, while larger structures were only modelled by the force field (MM+). Strong interactions were found by extended stacking of chlorins which are in van der Waals contact. Extended hydrogen bonding networks upon stack pairing brought about by OH····O=C bonds (bond length ca. 2.2Å, angle 139–153°) between appropriately situated chlorin pairs and by electrostatic interactions lead to very large energy stabilizations. The structural features of a modelled 40mer BChl aggregate are in full accord with all spectroscopic and low-resolution structural information on the in-vitro and chlorosomal BChl aggregates. Most important, from the rotation angle between stacks of ca. 16° and the stack-to-stack distance of 7.6 Å a tubular structure can be extrapolated to form on further extension of the aggregate. It has a predicted diameter of about 5.4 nm (Mg-Mg distance), i.e. very similar to that found for the rod elements in the chlorosomes ofChloroflexus.Dedicated to J.J. Katz, pioneer in the study of chlorophyll aggregation.Dedicated to J.J. Katz, pioneer in the study of chlorophyll aggregation.