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Biomedical subjects

F Rojo

Publications and source records attributed to F Rojo.

81 records · Page 5Linked to original sources
PubMed1988

Fate of genetically-engineered bacteria in activated sludge microcosms.

The conclusions that can be derived from this study regarding the fate of the GEMs and their ability to degrade added pollutants are as follows: 1. Both GEMs were able to survive in the microcoms. Because Pseudomonas sp. B13 has been cultured for a long time in the laboratory, it was not expected to survive well in the microcosm. Surprisingly, it and the derivative GEMs persisted at a high population level of approximately 10(5) bacteria/ml. Pure culture studies had demonstrated an ability of FR1(pFRC20P) to readily degrade simultaneous mixtures of 3CB and 4MB. In the microcosms, however, the GEM did not perform as well as expected, particularly when confronted with a shock load of a 3CB and 4MB mixture. Thus, the microcosm studies may be of potential help for making predictions concerning environmental applications of GEMs. 2. Pseudomonas sp. B13 derivative strains FR1 and FR1(pFRC20P) were able to degrade low concentrations of substituted benzoates within the complex ecosystem of the activated sludge microcosm. A good deal of information concerning the degradation pathway for aromatics by Pseudomonas sp. B13 was already known. This allowed for the construction of the stable, regulated pathways for the degradation of substituted aromatic compounds in both GEMs and indicates that the construction of similar GEMs for the degradation of environmental pollutants is a promising experimental strategy. 3. There was not any demonstrable, adverse effect of GEM addition to the microbial population level in the microcosm. The GEMs were even able to function in a protective manner for the indigenous populations by buffering them against the adverse effects of addition of substituted benzoates. In contrast, for microcosms lacking GEM addition, a wash-out of the bacterial population in the microcosm occurred (data not shown). 4. Lateral transfer of new genetic information (xylXYZLS) from the GEM chromosome to indigenous microorganisms was not detected, whereas transfer of the hybrid, mobilizable pFRC20P carrying the gene for lactone isomerase did apparently occur. In this particular case, transfer may have been beneficial for the community as a whole if it increased the ecosystem's ability to cope with the presence of toxic pollutants. As more GEMs are constructed for specific biotechnological applications the diversity and complexity of microcosms used to study their fate and function will increase. The ability of such studies to predict a priori the fate of these microorganisms will help to develop strategies both to decrease the risks associated with introducing GEMs into the environment and to increase and regulate the capacity of GEMs to degrade toxic pollutants.(ABSTRACT TRUNCATED AT 400 WORDS)

Bacteria↗
PubMed1987

Assemblage of ortho cleavage route for simultaneous degradation of chloro- and methylaromatics.

Genetic engineering is a powerful means of accelerating the evolution of new biological activities and has considerable potential for constructing microorganisms that can degrade environmental pollutants. Critical enzymes from five different catabolic pathways of three distinct soil bacteria have been combined in patchwork fashion into a functional ortho cleavage route for the degradation of methylphenols and methylbenzoates. The new bacterium thereby evolved was able to degrade and grow on mixtures of chloro- and methylaromatics that were toxic even for the bacteria that could degrade the individual components of the mixtures. Except for one enzymatic step, the pathway was fully regulated and its component enzymes were only synthesized in response to the presence of pathway substrates.

Alcaligenes↗
PubMed1987

Variability in the posttranslational processing of penicillin-binding protein 1b among different strains of Escherichia coli.

Screening of a number of unrelated strains of Escherichia coli confirms the existence of at least two patterns of molecular forms for penicillin-binding protein 1b in E. coli cell envelopes. Our data support that the beta-form of this protein is produced by posttranslational modification of the alpha-form and suggest that the absence of the beta-form in some strains is due to a strain-dependent variability in the alpha-form processing mechanism.

Acyltransferases↗
PubMed1986

Biological activities specified by antibiotic resistance plasmids.

Bacteria can display resistance to a wide spectrum of noxious agents and environmental conditions, and these properties are often mediated by genes located on extrachromosomal DNA elements called plasmids. Replication, vertical and horizontal transmission and evolution of these elements are discussed, and examples of the genes responsible for the resistance phenotypes are given. Selective forces that drive the evolution of new combinations of bacterial properties of particular importance in clinical situations are analysed.

Anti-Bacterial Agents↗
PubMed1984

Analysis of the different molecular forms of penicillin-binding protein 1B in Escherichia coli ponB mutants lysogenized with specialized transducing lambda (ponB+) bacteriophages.

Penicillin-binding protein (pbp) 1b, the main DD-transpeptidase/transglycosylase of Escherichia coli, is normally present in the cell in three molecular forms alpha, beta and gamma, differentiated by their mobility in sodium dodecyl sulfate/polyacrylamide gel electrophoresis. The three molecular forms are enzymatically active in vitro and their relative amounts are kept fairly constant in most labelling experiments with radioactive beta-lactam antibiotics. In this paper, we have analyzed the expression of ponB (mrcB), the structural gene for pbp 1b, and the relation among the three forms of pbp 1b in ponB strains lysogenyzed by lambda 540 (ponB+) recombinant bacteriophages. Our data indicate that ponB is transcribed anti-clockwise on the E. coli chromosome and suggest that pbp 1b alpha is the first membrane-bound form of pbp 1b able to bind labelled beta-lactams, and is the precursor of pbp 1b beta which is, in turn, the precursor of pbp 1 beta gamma.

Acyltransferases↗
PubMed1984

Binding of 125I-labeled beta-lactam antibiotics to the penicillin binding proteins of Escherichia coli.

125I-Labeled derivatives of the beta-lactam antibiotics cephalexin, cephradine, cefaclor and 6-alpha-aminopenicillanic acid have been obtained by reacting these compounds with (125I)-Bolton-Hunter reagent. The following target proteins were found in Escherichia coli: (1) The derivatives of cephalexin, cefaclor and cephradine preferentially interact with the high molecular weight penicillin binding proteins ( PBP1a and PBP1b ); (2) The 125I- derivative of 6-alpha-aminopenicillanic acid is preferentially bound by the low molecular weight penicillin binding proteins 4 and 5/6. The iodinated derivatives showed a very high affinity of binding to their target proteins with apparent half-saturating concentrations in the nano -molar range.

Ampicillin↗
PubMed1982

Interaction of beta-lactam antibiotics with penicillin-binding proteins from Bacillus megaterium.

The binding properties of 25 beta-lactam antibiotics to Bacillus megaterium membranes have been studied. The affinities of the antibiotics for the penicillin-binding proteins (PBPs) are also reported. We found that PBP 4 has the highest affinity for nearly all the antibiotics studied whereas PBP 5 has the lowest affinity. Both PBP 4 and PBP 5 appear to be dispensable for the maintenance of bacterial growth and survival and appear to be DD-carboxypeptidases. Only the beta-lactam cefmetazol bound preferentially to PBP 5 and has been used to study the inhibition of DD-carboxypeptidase. Comparative studies with beta-lactam that simultaneously result in (a) binding to PBPs 1 and 3, (b) inhibition of cell growth and (c) lysis, stressed the importance of PBPs 1 and 3 for cell growth and survival.

Anti-Bacterial Agents↗
PubMed1982

Carbenicillin resistance of Pseudomonas aeruginosa.

Four strains of Pseudomonas aeruginosa obtained from clinical isolates which are carbenicillin resistant were studied to find the cause(s) of resistance to this beta-lactam antibiotic. The electrophoresis patterns of the four strains (PH20610, PH20815, PH4011, and PH4301) were found to be different from those of a wild-type strain, P. aeruginosa NCTC 10662, and appeared to lack penicillin-binding protein 2. Affinity of other penicillin-binding proteins from strains PH20610 and PH20815 for carbenicillin seemed to be normal or slightly diminished. Electrophoretic patterns of penicillin-binding proteins from strains PH4011 and PH4301 had more profound differences, since the affinities of their penicillin-binding proteins 1a, 1b, and 4 for carbenicillin were decreased by nearly two orders of magnitude relative to the preparations from the wild-type strain. Kinetic studies on binding of carbenicillin to penicillin-binding proteins both in isolated membrane preparations and in intact cells revealed that carbenicillin penetration into resistant cells was a much slower process than in susceptible cells, suggesting that the outer envelope structures serve as an efficient barrier against carbenicillin entry into our P. aeruginosa strains from clinical isolates.

Bacterial Proteins↗