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Biomedical subjects

R Guerrero

Publications and source records attributed to R Guerrero.

At least 127 records · Page 7Linked to original sources
PubMed1983

Indirect induction of SOS functions in Salmonella typhimurium.

Infection of non-UV-irradiated cells of Salmonella typhimurium with UV-damaged P22 or KB1 phage induces recA-dependent inhibition of cell division, cell mutagenesis and prophage induction but not inhibition of respiration. On the contrary, respiration and ATP concentration are increased after treatment with UV-damaged phage in both RecA+ and RecA- strains, showing that this increase is not recA-dependent. Furthermore, infection with UV-damaged phage prevents both inhibition of respiration and decrease in ATP level in the UV-irradiated RecA+ strain. This indirect induction of SOS functions is related to degradation of phage DNA as well as to the multiplicity of infection used, suggesting that DNA degradation may play an important role in the mechanism of expression of the SOS system. Our results give also support to the hypothesis that there exists a differentiation in the expression of the various SOS functions.

Salmonella Phages↗
PubMed1983

Discriminated induction of SOS functions in Escherichia coli by alkylating agents.

Treatment of Escherichia coli with the alkylating agents diethyl sulphate, ethyl methane-sulphonate and N-methyl-N'-nitrosoguanidine produces a different pattern of expression of SOS functions. There is a full induction of recA-dependent inhibition of cell respiration, a slight induction of lambda prophage, and no inhibition of cellular division. In a comparative study with bleomycin, an agent which is able to induce these three SOS functions, we have also shown that the differences in expression of SOS functions are not due to any variation in the pattern of DNA synthesis, or DNA degradation after treatment with alkylating agents. These results suggest that the kind of damage induced in the DNA may be important in determining which SOS function is expressed.

Alkylating Agents↗
PubMed1983

Comparison between direct methods for determination of microbial cell volume: electron microscopy and electronic particle sizing.

Size frequency distributions of different phototrophic and heterotrophic microorganisms were determined by means of scanning and transmission electron microscopy and electronic particle sizing. Statistically significant differences existed among the three techniques used in this study. Cells processed for electron microscopy showed lower mean cellular volumes than those processed for electronic particle sizing, reflecting a shrinkage by factors ranging from 1.1 to 6.2 (mean, 2.3). Processing of cells for scanning electron microscopy caused higher shrinkage than processing for transmission electron microscopy. Shrinkage was dependent neither on the size nor on the cell wall type of the microorganism. When processed for scanning electron microscopy, phototrophic bacteria were strongly shrunken, whereas heterotrophic microorganisms were less affected. A direct relationship existed among phototrophic bacteria between percentage of shrinkage and specific pigment content. This was probably a consequence of the pigment extraction by organic solvents during the dehydration process, previous to the critical point drying, necessary to examine the specimens under the scanning electron microscope.

Bacteria↗
PubMed1983

Ecology and Physiology of the Competition for Light Between Chlorobium limicola and Chlorobium phaeobacteroides in Natural Habitats.

Accurate studies of the pigment composition and isolation in pure cultures of Chlorobiaceae from samples of eight Spanish lakes show that there are two main coexisting groups of green and brown Chlorobium spp. represented respectively by Chlorobium limicola and Chlorobium phaeobacteroides. Laboratory experiments with pure and mixed cultures of the isolated strains show that light quality plays a selective role on the species composition among Chlorobiaceae. This selection depends on the pigment composition which determines the in vivo absorption spectrum of the cells as well as on their ability to adjust the intracellular concentration of light-harvesting pigments to the spectral distribution and energy of light. Correlation analysis performed with field data resulted in significant, but low, correlation coefficients. Nevertheless, they were consistent with laboratory data showing that brown Chlorobiaceae were dominant in deep layers in meromictic lakes, whereas green Chlorobiaceae dominated in layers nearer the surface or underneath plates of Chromatiaceae. The combination of laboratory and field observations stress the role of biological light filtering in determining the species composition among Chlorobiaceae in lakes.

Journal Article↗
PubMed1983

Factors determining annual changes in bacterial photosynthetic pigments in holomictic lake cisó, Spain.

The pigments and biomass of anoxygenic phototrophic bacteria were measured during a year cycle in Lake Cisó (Girona, Spain). Two genera, Chromatium and Chlorobium, accounted for most of the bacterial population. The bacteria were present throughout the year despite complete mixing of the lake during fall and winter. This was possible because the sulfide production in the sediment was high enough to make the lake anaerobic to the very surface. Solar radiation, temperature, and biomass of Chromatium sp. were found to be important in determining pigment concentrations by correlation analysis. Sulfide concentration and biomass of Chlorobium spp. were found to be unimportant. A path analysis was performed to determine what percentage of the variability of pigments could be explained by the variables studied. Since a high percentage could be explained, it was possible to conclude that solar radiation, temperature, and biomass of Chromatium sp. were the main variables.

Journal Article↗
PubMed1983

Surgeons and operating rooms: underutilized resources.

A classification of surgical procedures, based on degree of complexity and the need for facilities and personnel, was applied to all 50,782 surgical interventions performed in the Valle del Cauca, Colombia during 1974. Three-fourths of all operations were of low levels of complexity, and most could be performed on an ambulatory basis with immediate discharge after recovery from anesthesia. Mean numbers of operations per year for surgical specialists and other physicians were 119.7 and 18.1, respectively. The 76 existing operating rooms were utilized only 41.6 per cent of the time. The implications of underutilization of personnel and facilities and low productivity of surgeons are discussed.

Colombia↗
PubMed1982

Familial idiopathic hypertrophic osteoarthropathy and cranial suture defects in children.

Three children with idiopathic hypertrophic osteoarthropathy and cranial suture defects are reported. The syndrome was recognized after birth and in the two oldest siblings, the cranial defects and subperiosteal bone formation resolved almost completely by age 4 and 6 years. The joint swelling and clubbing persisted and mild bone reabsorption of the distal phalanges became apparent at an older age. Two siblings and both parents had normal bone X-rays and no clubbing. This study confirms the association of cranial sutural defects and familial idiopathic hypertrophic osteoarthropathy.

Abnormalities, Multiple↗
PubMed1982

Expression of recA-gene dependent SOS functions in Salmonella typhimurium.

Thymine starvation of RecA+ Thy- strains of Salmonella typhimurium does not induce the inhibition of cellular respiration, one of the recA-gene dependent SOS functions. Nevertheless, thymine deprivation is able to produce a normal induction of prophage and thymineless death in these same strains However, when these mutants are treated, in the presence of thymine, with UV-irradiation or bleomycin, they show a normal inhibition of cellular respiration and other SOS functions. Thus, one injurious treatment (thymine deprivation) may trigger prophage induction but not cessation of respiration, whereas another agent (UV-irradiation) may induce both. Together, these results suggest a possible discrimination in the pathways and conditions of expression of various SOS functions.

Bleomycin↗
PubMed1981

A mutant of Salmonella typhimurium with an abnormal septation pattern associated with an inhibition of RNA synthesis.

A mutant strain of S. typhimurium that is disturbed in the regulation of cell division and macromolecular synthesis is described. The life cycle of the mutant can be divided into two discrete stages. When growing in rich medium at a low cell density, cell division is inhibited and the cells filament at the same time as the relative amount of RNA shows a continuous increase. However, at a certain stage, RNA synthesis stops and the filaments start to septate resulting in chain-formation. These chains can thereafter segregate into individual cells of unit cell length. The accumulation of RNA is rather due to a regulatory defect in th synthesis of ths stable RNA species than to a unusual stability of messenger RNA (mRNA) as the half life of mRNA was estimated to 2.3 minutes during the period of RNA accumulation. Latter inhibition of RNA synthesis affects only stable species of RNA. The ppGpp pools of the strain did not fluctuate during growth, showing that inhibition of RNA. The ppGpp pools of the strain did not fluctuate during growth, showing that inhibition of RNA synthesis is not correlated to changes in the level of ppGpp. Different treatments that reduce the level of transcription such as sublethal concentrations of rifampicin, shift-down or high concentrations of nalidixic acid, all induced cell division of filamentous cells, suggesting that there exists an intimate relationship between macromolecular synthesis and cell division. The behavior of this mutant its best with the proposed hypothesis that the biomass to volume ratio is of importance in the regulation of cell division in bacteria.

Cell Division↗
PubMed1981

[Burkitt's lymphoma. Report of six cases (author's transl)].

Authors report six cases on Burkitt's lymphoma seen during the last 18 months. In all of them a large ileocecal tumor was present and five of them had a bone marrow involvement. The ascitic fluid was positive in all cases. Three of the patients had a marked jaundice at diagnosis. The immunologic markers study on two of the cases, made evident that they belonged to type B. One of these two cases showed a component M in serum of the IgM type. As soon as chemotherapy started two of the cases showed marked metabolic disturbances. Three of the cases died and the three others remain free of disease for as long as two, 26 and 21 months. This report arises a comment epidemiologic importance of the increased frequency of Burkitt's lymphoma during the last months, as well as the clinic features of the six reported cases as compared to series published in non endemic areas on this topic.

Ascites↗
PubMed1980

Surface density of major outer membrane proteins in Salmonella typhimurium in different growth conditions.

The amount of major proteins per unit of surface area in the outer membrane (OM) of Salmonella typhimurium LT2 remained constant during steady-state growth in different media. Between growth rates of 2.40 doublings h-1 and 0.31 doublings h-1, the surface density of major OM proteins varied between 0.9 X 105 molecules per micrometer2, while surface area per cell more than halved. The accumulation of molecules of the major OM proteins was not affected by addition of cyclic AMP to the growth medium. When exponentially growing cells were subjected to shift-up transitions, cell dimensions began to increase after a lag period of 20 min. Accumulation of major OM proteins followed the same pattern as total protein; this created a transitory imbalance of major OM protein density in the shift from acetate minimal medium to LB medium, before the steady situation was reached. After shift-down transitions, cell dimensions began to decrease immediately, cells eventually becoming shorter than in steady-state conditions. No fluctuations in major OM protein density were observed during the shift-down, although final stable levels differed from those in steady-state conditions. All these results indicate that bacteria adapt the accumulation of major proteins into the OM according to the amount of surface. Thus, no large differences exist at different cell sizes, although transitions between media can lead to transitory or stable changes in the composition of the OM.

Bacterial Proteins↗
PubMed1979

Ovum transport in women treated with methyl ergonovine.

The location of ova in the genital tract was studied between 24 and 120 hours after the luteinizing hormone (LH) surge in 32 women who had been treated with methyl ergonovine in doses known to stimulate tubal contractility. Thirteen eggs were found in the fallopian tubes, between 48 and 120 hours after th LH peak, and no eggs were recovered from the endoemtrial cavity. No significant difference in tubal ovum recovery or in tubal segmental distribution of ova was found in comparison with these parameters in an untreated control group. These results indicate that stimulation of tubal contractility with methyl ergonovine does not accelerate ovum transport through the fallopian tubes in the human.

Ergonovine↗