Immumoglobulin allotypes in Ecuadorian Cayapa Indians

Indigenous Indian groups comprise approximately 20% of Ecuador's population, the third largest percentage in all of Central or South America, yet immunogenetic data on these groups are lacking in the literature. In the course of population migration studies, sera collected from 65 Ecuadorians living in the northern province of Esmeraldas were typed for six GM and two KM markers. The study population consisted of 47 Cayapa Indians and 18 blacks of African origin, descendants of slaves imported into the area during the seventeenth century. The Cayapa demonstrated three GM phenotypes, two of which are common to other South American Indian tribes. The frequency of KM1 positive Cayapa Indians (63%) is similar to other South American Indian tribes, but is significantly greater than the Huaorani of eastern Ecuador (2%), the only other Ecuadorian Indian group for whom limited immunoglobulin allotype data are available ( ²=35.8, P<0.0001).     

A descriptive study of some Antarctic notaspidean opisthobranchs (Gastropoda), with description of a new genus and species

During the expedition “ANTARTIDA 9101”, organized by the Spanish Oceanographic Institute to the South Orkney Islands, four specimens of notaspidean gastropods were collected. Three of them have been identified as Bathyberthella antarctica Willan and Bertsch, 1987. However, one specimen, although externally similar to B. antarctica, had an internal anatomy exhibiting features that have enabled us to consider it to be a new genus and species. This new taxon is characterized by the presence of jaws without mandibular elements, and a vaginal gland that partially surrounds the distal region of the vaginal duct. In this paper the new genus and species is described. Additional anatomical data of the specimens of B. antarctica collected during the expedition are also included.     

Supercritical carbon dioxide extraction of hydrocarbons from the microalgaBotryococcus braunii

Samples of the microalgaBotryococcus braunii were submitted to supercritical fluid extraction with carbon dioxide at 40 °C and pressures of 12.5, 20.0 and 30.0 MPa. The extraction yield and the fraction of the hydrocarbons in the extracts both increased with pressure and at 30 MPa these compounds were obtained rapidly. This behaviour is associated with the localization of the hydrocarbons outside the cell wall. In the extracts, which are fluid, golden and limpid, chlorophyll and phospholipids were not detected.Author for correspondence     

Plasma membrane Ca2+ channels in roots of higher plants and their role in aluminium toxicity

Single Ca²⁺ channel records were obtained from plasma membrane-enriched fractions of wheat roots incorporated into artificial planar lipid bilayers. The channel had a unitary conductance of 15 pS for a 10 to 95 mM CaCl₂ gradient (cytoplasm: outside of the cell). The voltage dependence displayed by the channel agreed with that expected for Ca²⁺ channels in the plasma membrane. The channel gating was strongly modified by addition of 20 M extracellular verapamil (a Ca²⁺ channel antagonist). Extracellular AlCl₃ (70 M, pH 4.9) almost completely blocked the channel.     

Expression of mutations and protein release by yeast conditional autolytic mutants in batch and continuous cultures

Thermosensitive mutant strains of Saccharomyces cerevisiae that fail to generate an osmotically stable cell wall when grown at a non-permissive temperature release their cell contents upon expression of the mutation. Therefore, they may represent an alternative for the production of homologous or heterologous protein preparations. In order to analyse the expression of two of these mutations, lyt2 and slt2, we grew the corresponding strains under precisely defined conditions in batch and continuous fermentors. A switch in the temperature of batch cultures from 24° C to 37° C determined lysis of the cells with a significant release of intracellular enzymes. These include alkaline phosphatase and periplasmic proteins such as glucan-degrading enzymes, the pattern of cell lysis and protein release being maintained for about 6 h. One-stage continuous cultures of a lyt2 mutant were maintained for long periods at 37° C; a fraction of the population lysed and released the indicated proteins, but eventually a revertant of the lytic phenotype was selected. To avoid this, a two-stage continuous culture system was developed by connecting two fermentors in series, the effluent from the first one at 24°C being fed to the second one adjusted to 37° C. A steady state of cell lysis and protein liberation was reached in the second-stage fermentor without any evidence of selection of revertants. This system can be very useful for developing conditions for the use of yeast strains to produce protein preparations. Correspondence to: C. Nombela     

A qualitative mathematical model of the ontogeny of a circadian rhythm in crayfish

Based on experimental work on the ontogeny of the electroretinogram circadian rhythm in crayfish, we present a mathematical model simulating changes in both frequency and amplitude of the electroretinogram oscillation during several developmental stages until shortly before the adult age. Simultaneously, we propose a hypothetical oscillation in the hormonal release whose frequency is imposed on the electroretinogram oscillation. The model consists of two coupled nonlinear oscillators in which a dynamical response is obtained mainly through an Andronov-Hopf bifurcation. Through the construction of the model, a biological hypothesis about the essential elements underlying the ERG circadian rhythm and their interrelations is formulated and discussed.     

Life-history studies of heterophyid trematodes in the Neotropical Region: Ascocotyle (Phagicola) diminuta (Stunkard & Haviland, 1924) and A. (P.) angrense Travassos, 1916

The life-cycle of Ascocotyle (Phagicola) diminuta (Stunkard & Haviland, 1924) was reproduced experimentally, starting from cercariae from naturally infected Littoridina castellanosae and L. parchappei (Hydrobiidae) collected from artificial ponds in the Zoological Garden in Buenos Aires and from Los Ranchos stream, Buenos Aires Province, respectively. Metacercariae were found encysted in the gills of experimentally exposed Cnesterodon decemmaculatus (Poecilidae) and of other naturally infected freshwater fishes. Adults were obtained experimentally in chicks and mice and from a naturally infected egret, Egretta thula. A. (P.) angrense Travassos, 1916 was found parasitising the egret Ixobrychus involucris; it is considered a valid species and the morphological differences between it and A. (P.) diminuta were established. The “Phagicola-form” of the cercaria in the present life-cycle is also known in the genus Pygidiopsis.     

A highly conserved α-tubulin sequence from Prunus amygdalus

The sequence of an -tubulin from Prunus amygdalus has been obtained by cDNA cloning. When this sequence is compared to that of the Tub1 gene from maize it shows a very high degree of similarity, much higher than any of the -tubulin sequences reported so far from plants. The expression of this gene is high in the stages of seed development where a high divisional activity is present. It is preferentially expressed in the radicular tissues as it is gene Tub1 in maize. Southern analysis indicates that this gene may from a subfamily of -tubulin genes having similar sequence and tissue specificity and existing at least in maize and in Prunus.     

A pulsing device for packed-bed bioreactors: II. Application to alcoholic fermentation

When the immobilized cells are employed in packed-bed bioreactors several problems appear. To overcome these drawbacks, a new bioreactor based on the use of pulsed systems was developed [1]. In this work, we study the glucose fermentation by immobilized Saccharomyces cerevisiae in a packed-bed bioreactor. A comparative study was then carried out for continuous fermentation in two packed-bed bioreactors, one of them with pulsed flow. The determination of the axial dispersion coefficients indicates that by introducing the pulsation, the hydraulic behaviour is closer to the plug flow model. In both cases, the residence time tested varied from 0.8 to 2.6 h. A higher ethanol concentration and productivity (increases up to 16%) were achieved with the pulsated reactors. The volumes occupied by the CO₂ were 5.22% and 9.45% for fermentation with/without pulsation respectively. An activity test of the particles from the different sections revealed that the concentration and viability of bioparticles from the two bioreactors are similar. From the results we conclude that the improvements of the process are attributable to a mechanical effect rather than to physiological changes of microorganisms.List of Symbols D m²/s dispersion coefficient - K _is l/g inhibition substrate constant - K _ip l/g inhibition ethanol constant - K _s g/l Apparent affinity constant - P g/l ethanol concentration - q _p g/(gh) specific ethanol productivity - Q _p g/(lh) overall ethanol productivity - q _s g/(gh) specific glucose consumption rate - Q _s g/(lh) glucose consumption rate - S g/l residual glucose concentration - S(in0) g/l initial glucose concentration - V _max g/(lh) maximum rate - Y _p/s g/g yield in product     

Molecular cloning and analysis of CDC28 and cyclin homologues from the human fungal pathogen Candida albicans

In the budding yeast Saccharomyces cerevisiae, progress of the cell cycle beyond the major control point in G1 phase, termed START, requires activation of the evolutionarily conserved Cdc28 protein kinase by direct association with GI cyclins. We have used a conditional lethal mutation in CDC28 of S. cerevisiae to clone a functional homologue from the human fungal pathogen Candida albicans. The protein sequence, deduced from the nucleotide sequence, is 79% identical to that of S. cerevisiae Cdc28 and as such is the most closely related protein yet identified. We have also isolated from C. albicans two genes encoding putative G1 cyclins, by their ability to rescue a conditional GI cyclin defect in S. cerevisiae; one of these genes encodes a protein of 697 amino acids and is identical to the product of the previously described CCN1 gene. The second gene codes for a protein of 465 residues, which has significant homology to S. cerevisiae Cln3. These data suggest that the events and regulatory mechanisms operating at START are highly conserved between these two organisms.