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Biomedical subjects

R Guerrero

Publications and source records attributed to R Guerrero.

At least 109 records · Page 6Linked to original sources
PubMed1986

Ciliates from a fresh water sulfuretum.

Ciliates were collected from a freshwater sulfuretum, Lake Cisó, which is part of a gypsum karstic area whose main feature is Lake Banyoles (Girona, Spain). Chromatium, Lamprocystis and Chlorobium are the major phototrophic sulfur bacteria in Lake Cisó. Blooms of a photosynthetic cryptomonad (up to 5 X 10(5) ind ml-1) were found at the metalimnion. The community of ciliates could be divided in three groups: aerobic, cosmopolitan, genera such as Stentor and Vorticella, in the epilimnion; a large population (up to 10(4) ind ml-1) of Coleps, adapted to low concentrations of both oxygen and sulfide, together with a few individuals of the equally sulfide-tolerant genus Paramecium, in the metalimnion, and anaerobic, true sulfide-loving genera such as Plagiopyla and Metopus, in the hypolimnion, where sulfide concentration was between 0.6 and 1.2 mM.

Animals↗
PubMed1986

Predatory prokaryotes: predation and primary consumption evolved in bacteria.

Two kinds of predatory bacteria have been observed and characterized by light and electron microscopy in samples from freshwater sulfurous lakes in northeastern Spain. The first bacterium, named Vampirococcus, is Gram-negative and ovoidal (0.6 micrometer wide). An anaerobic epibiont, it adheres to the surface of phototrophic bacteria (Chromatium spp.) by specific attachment structures and, as it grows and divides by fission, destroys its prey. An important in situ predatory role can be inferred for Vampirococcus from direct counts in natural samples. The second bacterium, named Daptobacter, is a Gram-negative, facultatively anaerobic straight rod (0.5 x 1.5 micrometers) with a single polar flagellum, which collides, penetrates, and grows inside the cytoplasm of its prey (several genera of Chromatiaceae). Considering also the well-known case of Bdellovibrio, a Gram-negative, aerobic curved rod that penetrates and divides in the periplasmic space of many chemotrophic Gram-negative bacteria, there are three types of predatory prokaryotes presently known (epibiotic, cytoplasmic, and periplasmic). Thus, we conclude that antagonistic relationships such as primary consumption, predation, and scavenging had already evolved in microbial ecosystems prior to the appearance of eukaryotes. Furthermore, because they represent methods by which prokaryotes can penetrate other prokaryotes in the absence of phagocytosis, these associations can be considered preadaptation for the origin of intracellular organelles.

Bdellovibrio↗
PubMed1986

Effect of P22-mediated receptor release and of phage DNA injection on cell viability of Salmonella typhimurium.

Infection with u.v.-inactivated P22 bacteriophage at multiplicities higher than 30 caused a decrease in Salmonella typhimurium viability without cell lysis. Neither the action of the endoglycosidase of the P22 virion on the lipopolysaccharide of S. typhimurium nor the concomitant release of cell wall components was responsible for m.o.i.-dependent cell death. Using both free P22 tails and u.v.-inactivated P22, we have shown that p9 tail protein activity has no effect either on the integrity of host cells or on cell viability. Our results show that cell death is due to the injection of the u.v.-inactivated P22 DNA.

Adsorption↗
PubMed1986

Effect of alkylating agents on the expression of inducible genes of Escherichia coli.

Increasing doses of alkylating agents such as N-methyl-N'-nitro-N-nitrosoguanidine, diethyl sulphate and ethylmethane sulphonate cause an inhibition of the expression of the recA and sfiA genes of wild-type Escherichia coli. This behaviour was not observed in a lexA56 mutant which has a defective LexA repressor that is unable to bind to the SOS operator. Furthermore, an ada-1 mutant showed the same behaviour as the wild-type strain indicating that the adaptive proteins are not responsible for the inhibition of recA and sfiA at high doses of alkylating agents. These results suggest that the inhibitory effect of these alkylating agents may be found in the interaction between the LexA repressor and the control regions of sfiA and recA. On the other hand, high doses of either UV light or mitomycin C produced only a slight decrease in the induction of recA and sfiA, whereas bleomycin had no effect. The fact that a repressor structurally related to LexA repressor, such as LacI protein, showed the same behaviour as the LexA repressor when a Lac+ strain was treated with alkylating agents, suggests that these compounds can modify the binding abilities of repressors to DNA, producing a limited or even abolished release of repressors, and so decreasing the expression of inducible genes.

Alkylating Agents↗
PubMed1986

Characterization of SE1, a new general transducing phage of Salmonella typhimurium.

A transducing phage, SE1, which is able to infect Salmonella typhimurium was isolated from a Salmonella enteritidis strain. SE1 is a temperate phage which is heteroimmune with respect to phages P22, L, KB1 and ES18. It is similar in morphology and size to phages P22, L and KB1 and is serologically related to phages P22 and L but not to KB1. Efficiencies of generalized transduction effected by phage SE1 are similar to those for P22HT (int7), a mutant which mediates a high frequency of chromosomal gene transduction. The lengths of chromosomal DNA transduced by SE1 and P22HT (int7) are similar. Furthermore, the SE1 prophage does not exclude the transducing particles from cells it has lysogenized; consequently it is possible to use both SE1 lysogens and non-lysogenic strains as recipients in SE1-mediated transduction experiments, and obtain similar transduction efficiencies. However, the SE1 prophage gives rise to a lysogenic conversion that decreases the rate of adsorption of SE1 and L phages by about 50%, but does not affect adsorption of P22. Altogether these results suggest that phage SE1 may be a useful tool in the genetic manipulation of S. typhimurium.

Antigens, Bacterial↗
PubMed1986

ATP hydrolysis during SOS induction in Escherichia coli.

Changes in cellular ATP concentration during SOS induction in strains of Escherichia coli with different levels of RecA and LexA proteins were studied. UV irradiation of RecA+ strains induced a twofold increase in the ATP concentration around the first 20 min, followed by a decrease to the values of nonirradiated cells. On the other hand, mutants defective in RecA protein or with either deficient RecA protease activity or cleavage-resistant LexA repressor did not show any decrease, suggesting that ATP consumption is related to LexA repressor hydrolysis. Furthermore, strains presenting a constitutive synthesis of RecA protein showed the same changes in ATP concentration as the wild-type strain. Likewise, the presence in a RecA+ strain of a LexA(Def) protein, which is defective in its capacity for binding specifically to SOS operators, did not disturb the changes in ATP when compared with the LexA+ RecA+ strain. Moreover, after UV irradiation, a LexA(Def) RecA- double mutant showed an important increase in ATP concentration, which remained elevated for at least 120 min after UV treatment.

Adenosine Triphosphate↗
PubMed1985

Further characterization of SOS system induction in recBC mutants of Escherichia coli.

Expression of several SOS functions such as induction of lambda prophage, inhibition of cell division and induction of both umuC and recA genes after UV-irradiation, nalidixic acid or mitomycin C addition was studied in an RecBC- mutant. UV-irradiation and mitomycin C induced all SOS functions studied in the RecBC- cells but at a lower level and delayed with respect to the wild-type strain. On the contrary, nalidixic acid was unable to trigger any of these SOS functions. In the RecBC- mutant, adenine only had a stimulating effect on the amplification of RecA protein synthesis following UV-irradiation. Nevertheless, in the wild-type strain the stimulating effect occurred in all SOS functions studied following UV-irradiation as well as in the amplification of RecA protein synthesis by nalidixic acid but not in the other SOS functions triggered by this compound. Furthermore, adenine produced a decrease in the mitomycin C-mediated induction of all SOS functions studied in both RecBC- and wild-type strains.

Adenine↗
PubMed1985

A case-control study of BCG and childhood tuberculosis in Cali, Colombia.

We conducted a case-control study to evaluate the effectiveness of BCG vaccination in preventing childhood tuberculosis (TB) in Cali, Colombia. We ascertained 178 cases aged 0 to 14 years from the respiratory clinics with cough or fever for at least three weeks and a positive chest X-ray for TB, as well as 320 controls who were from the same households but had no symptoms and negative X-rays. Using matched set multiple logistic regression analysis, we found the age- and sex-adjusted relative risk (RR) of TB among vaccinees compared with non-vaccinees to be 0.84 with 95% confidence limits (CL) from 0.43 to 1.62. There was, however, a significantly lowered relative risk of TB with increasing time since vaccination (RR = 0.83 per year since time of vaccination with 95% CL from 0.74 to 0.94.)

Adolescent↗
PubMed1985

Effect of adenine, cytidine and guanosine on the expression of the SOS system in Escherichia coli.

Addition of cytidine or guanosine to UV-irradiated cells of a RecA+ strain of Escherichia coli did not produce any effect on the induction of two SOS functions: inhibition of cell division and expression of the umuC gene. Under the same conditions adenine gave a slight increase in the induction of these two responses. In a RecA441 mutant growing at 42 degrees C, both cytidine and guanosine inhibited these SOS functions, whereas adenine produced a large increase in their expression. Moreover, the ATP concentration of the RecA441 mutant at 42 degrees C showed a decrease which occurred earlier in the cells growing in the presence of cytidine or guanosine than in the absence of either compound. Adenine induced an increase of about three times the initial ATP concentration of this mutant at 42 degrees C which dropped quickly after 10 min. Neither cytidine nor guanosine increased the evolution of cellular ATP in UV-irradiated cells of the RecA+ strain, whereas adenine had only a slight positive effect. However, in UV-irradiated RecA+ cells with and without adenine, ATP levels dropped quickly to the initial value after 20 min. These data suggest that the influence of adenine, cytidine and guanosine on the expression of the RecA441 phenotype at 42 degrees C may be due to alteration of the cellular ATP concentration of this mutant.

Adenine↗
PubMed1985

Mathematical model for determining the effects of intracytoplasmic inclusions on volume and density of microorganisms.

Procaryotic microorganisms accumulate several polymers in the form of intracellular inclusions as a strategy to increase survival in a changing environment. Such inclusions avoid osmotic pressure increases by tightly packaging certain macromolecules into the inclusion. In the present paper, a model describing changes in volume and density of the microbial cell as a function of the weight of the macromolecule forming the inclusion is derived from simple theoretical principles. The model is then tested by linear regression with experimental data from glycogen accumulation in Escherichia coli, poly-beta-hydroxybutyrate accumulation in Alcaligenes eutrophus, and sulfur accumulation in Chromatium spp. The model predicts a certain degree of hydration of the polymer in the inclusion and explains both the linear relationship between volume of the cell and weight of the polymer and the hyperbolic relationship between density of the cell and weight of the polymer. Other implications of the model are also discussed.

Alcaligenes↗
PubMed1985

Expression of the SOS genes of Escherichia coli in Salmonella typhimurium.

To lysogenize Salmonella typhimurium by Lambda phage, a region of 10.2 kb of Escherichia coli DNA carrying the nusA gene was cloned in a S. typhimurium strain containing a F'112 plasmid which codifies for the lamB region of E. coli. The strain of S. typhimurium obtained in this way, was lysogenized by lambda c IndO- bacteriophage harboring either a fusion between recA1 or sfiA genes of E. coli with lacZ gene. Likewise, pSE143 plasmid with a umu C::lacZ fusion was introduced in S. typhimurium. Afterwards, induction of these SOS genes was studied. Results obtained show that the basal transcription of both recA and sfiA genes of E. coli was higher in S. typhimurium than in E. coli. Nevertheless, induction of recA and sfiA genes by UV-irradiation and mitomycin C was higher in E. coli than in S. typhimurium. On the other hand, umuC gene of E. coli presents the same basal level of transcription in both E. coli and S. typhimurium species, although induction of this gene by UV-irradiation and mitomycin C was higher in S. typhimurium than in E. coli. Therefore, the plasmid pUA25 constructed in this work may be used to introduce, using the Lambda phage as a vector, the SOS genes of E. coli in other bacterial species which may be useful to study the relationship between their respective SOS systems.

Bacterial Proteins↗
PubMed1985

A survey of buoyant density of microorganisms in pure cultures and natural samples.

Values of buoyant density of microorganisms reported in literature are widely divergent because of techniques used. Many of these involve centrifugation in density gradients formed by substances with high osmolarity which dehydrate the cells. In order to better understand the ranges of variation of density of microbial cells several approaches were taken. Firstly, samples from several natural aquatic habitats were taken and the densities of the microorganisms present determined. Secondly, experiments were performed with selected microorganisms to maximize density changes by forcing them to accumulate intracytoplasmic inclusions of dense materials or to loose their capsules. Finally, the relevant literature was reviewed. It could be demonstrated that most microorganisms have a density around 1.080 pg microns-3 when measured in low osmolarity media such as Percoll. However, many species are able to modify their density by as much as 7% (for instance, from 1.097 to 1.022 pg microns-3 in Thiocapsa roseopersicina, and similar variations in other bacteria), by incorporating substances into inclusions (sulfur, carbon, phosphorous storage materials, etc.), or by making capsules and/or gas vesicles. The relevance of buoyant density determinations for several aspects of microbial ecology and physiology is discussed.

Bacteria↗
PubMed1984

Effect of L-ethionine on the expression of the SOS system in Escherichia coli.

The effect of L-ethionine, the ethyl analog of the essential amino acid methionine, on the SOS system of Escherichia coli was studied. This compound does not induce either inhibition of cell division nor cessation of cell respiration in a RecA+ Met+ RelA+ strain, nor in RecA+ Met- RelA+ or RecA+ Met- RelA- mutants. Nevertheless, L-ethionine blocks the expression of both cited SOS functions in a recA441 mutant when it is growing at the restrictive temperature of 42 degrees C. Furthermore, the inhibitory effect of the L-ethionine on the induction of the SOS system in this mutant is increased when the cells are preincubated for several hours in the presence of the analog, before the temperature shift. Moreover, cultures of the recA441 mutant incubated at 42 degrees C in the presence of both L-ethionine and L-methionine present the same behaviour as the cultures of this mutant growing at the same temperature but without either amino acid. On the other hand, L-ethionine does not have any effect on the expression of the two mentioned SOS functions when these are induced by UV-irradiation in a RecA+ strain even if this compound is added to the cells several hours before irradiation.

DNA Repair↗
PubMed1984

Nematoda: Trichostrongyloidea parasites of Venezuelan wild mammals. III. The genus Vexillata Travassos, 1937.

Two new species of the genus Vexillata Travassos, 1937 parasitizing Heteromys anomalus of Venezuela are described, V. tejerai n. sp. and V. scorzai n. sp., both close to V. petteri Durette-Desset, 1970 and V. chabaudi Yoyotte-Vado, 1972, by possessing of 4 dorsal ridges and the dorsal rib divided near the tip. Both new species are differentiated from V. chabaudi by having the dorsal rib much shorter than rib 8; they are distinguished from V. petteri by having ribs 2 and 3 nearly the same size. The two new species are separated by the significantly greater size of V. tejerai and by the form of the copulatory bursa. A brief historical review of the genus is given, together with considerations on its origin and its probable relation to the Pudicinae or Brevistriatinae. A key to the 8 known species is also given.

Animal Population Groups↗
PubMed1984

Changes in ATP concentration in Escherichia coli during induction of the SOS system by mitomycin C and bleomycin.

Treatment of Escherichia coli with bleomycin induced a dramatic increase in ATP concentration in the first 30 min. Afterwards, in RecA+ strains, ATP dropped quickly to values similar to those of untreated cells. Mutants of E. coli defective in either RecA protein or RecA protease activity did not show this decrease, indicating that it was due to the action of RecA protease. The increase in ATP in the first 30 min was dependent on RecBC exonuclease activity and must have been due to substrate level phosphorylation, since an uncoupler such as dinitrophenol did not affect it. Nevertheless, mitomycin C did not induce any change in ATP pools of RecA+ strains, at least during 120 min following treatment. The implications of these findings are discussed in relation to the possible pathways of activation of RecA protease.

Adenosine Triphosphate↗
PubMed1983

Evolution of cellular ATP concentration after UV-mediated induction of SOS system in Escherichia coli.

UV-irradiation of E. coli induces a two fold increase in ATP pool in the first 20 min. Afterwards, in RecA+ strains ATP level drops quickly below values of non irradiated cells. Mutants of E. coli defective in RecA protein or with either RecA protease activity deficient or protease resistant LexA repressor do not present this decrease, showing that it is due to cleavage of LexA repressor by RecA protease. The ATP increase produced in the first 20 min is dependent on RecBC exonuclease activity and it must be due to substrate level phosphorylation since an uncoupler such as dinitrophenol does not affect it.

Adenosine Triphosphate↗