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P Renault

Publications and source records attributed to P Renault.

At least 19 recordsLinked to original sources
PubMed1996

Imbalance of leucine flux in Lactococcus lactis and its use for the isolation of diacetyl-overproducing strains.

Diacetyl is a by-product of pyruvate metabolism in Lactococcus lactis, where pyruvate is first converted to alpha-acetolactate, which is slowly decarboxylated to diacetyl in the presence of oxygen. L. lactis usually converts alpha-acetolactate to acetoin enzymatically, by alpha-acetolactate decarboxylase encoded by the aldB gene. We took advantage of the fact that this enzyme also has a central role in the regulation of branched-chain amino acids, to select spontaneous aldB mutants in an unbalanced concentration of leucine versus those of valine and isoleucine in the medium. Industrial dairy strains of L. lactis subsp. lactis biovar diacetylactis containing point mutations and deletions of aldB were isolated and characterized. Their growth in milk was not affected, but they rapidly accumulated a large amount of alpha-acetolactate instead of acetoin from citrate in milk. Under aerated condition, strains devoid of AldB produced about 10 times more diacetyl than did the parental strains.

Amino Acid Sequence↗
PubMed1996

Genetic manipulation of the pathway for diacetyl metabolism in Lactococcus lactis.

Diacetyl is an important food flavor compound produced by certain strains of citrate-metabolizing lactic acid bacteria. Citrate is converted to pyruvate, from which diacetyl is produced via intermediate alpha-acetolactate. This paper reports the cloning and analysis of the gene (aldB) encoding alpha-acetolactate decarboxylase from Lactococcus lactis MG1363. Deletion of the MG1363 chromosomal aldB gene was achieved by double crossover homologous recombination. The mutant strain was found to produce diacetyl; alpha-acetolactate decarboxylase activity was eliminated. Overexpression of the cloned ilvBN genes (encoding an alpha-acetolactate synthase) in the aldB deletion strain produced even higher levels of alpha-acetolactate, acetoin, and diacetyl.

Acetolactate Synthase↗
PubMed1995

Metabolic operons in Lactococci.

The genes for the biosynthesis of histidine, tryptophan and branched-chain amino acids (ilv for isoleucine, leucine and valine) are clustered in large operons. In addition to genes encoding the pathway enzymes, the his and the ilv operons contain 4 and 3 other genes, respectively. The functions of two of these, orf3 and aldB are regulatory. The second gene of the his operon, orf3, encodes a protein homologous to the histidyl-tRNA synthetases. It is involved in transcription attenuation upstream of the his operon. This regulation is related to a new class of attenuation mechanisms controlling the expression of most tRNA synthetase genes and a few metabolic operons in Gram-positive bacteria. Gene aldB, the penultimate gene of the ilv operon, encodes acetolactate decarboxylase. This enzyme transforms acetolactate (AL), the first intermediate of leucine and valine biosynthesis, into acetoin. AL decarboxylase is positively controlled by the availability of leucine and possibly valine in the cell. This is the key enzyme for a new class of regulatory mechanisms, a metabolic shunt which guides the AL flux towards synthesis of amino acids or a secondary metabolite.

Amino Acid Sequence↗
PubMed1995

Specificity of insertion of Tn1545 transposon family in Lactococcus lactis subsp. lactis.

A collection of Lactococcus lactis subsp. lactis strains carrying a derivative of Tn1545 inserted in the chromosome was generated. Some 34 insertions were cloned in Escherichia coli and the flanking DNA sequences determined. Insertions are distributed non randomly and several hot spots were observed. The hot spots do not have sequence features which would distinguish them from other insertion sites, suggesting that they may have special structural properties. Insertions in open reading frames occurred at a far lower frequency than expected for random transposition and were most often located near potential terminator and promoter sequences. Different mutations in the extremities of the transposon do not affect the specificity of insertion. We suggest that target specificity is mainly due to the properties of the intergrase itself.

Amino Acid Sequence↗
PubMed1994

Purification and properties of the alpha-acetolactate decarboxylase from Lactococcus lactis subsp. lactis NCDO 2118.

alpha-Acetolactate decarboxylase from Lactococcus lactis subsp. lactis NCDO 2118 was expressed at low levels in cell extracts and was also unstable. The purification was carried out from E. coli in which the enzyme was expressed 36-fold higher. The specific activity was 24-fold enhanced after purification. The main characteristics of alpha-acetolactate decarboxylase were: (i) activation by the three branched chain amino acids leucine, valine and isoleucine; (ii) allosteric properties displayed in absence and Michaelis kinetics in the presence of leucine. The enzyme is composed of six identical subunits of 26,500 Da.

Carboxy-Lyases↗
PubMed1994

Mosaic structure of large regions of the Lactococcus lactis subsp. cremoris chromosome.

Lactococcus lactis subsp. lactis and Lactococcus lactis subsp. cremoris are closely related phenotypically and genetically. Here we report that certain regions of their chromosomes diverge considerably more than others. Conserved regions differ by less than 20%, whilst variable regions differ by more than 60%. This mosaic structure may have arisen by horizontal gene transfer from distantly related bacteria since in a particular region of the L. lactis subsp. cremoris chromosome the G+C content and the codon bias are not typical for lactococci. Such an exchange, which conserves the function of the gene and cannot be achieved under selective pressure, may be of considerable importance in the evolution of bacteria.

Amino Acid Sequence↗
PubMed1993

Gene inactivation in Lactococcus lactis: branched-chain amino acid biosynthesis.

The Lactococcus lactis subsp. lactis strains isolated from dairy products are auxotrophs for branched-chain amino acids (leucine, isoleucine, and valine), while most strains isolated from nondairy media are prototrophs. We have cloned and sequenced the leu genes from one auxotroph, IL1403. The sequence is 99% homologous to that of the prototroph NCDO2118, which was determined previously. Two nonsense mutations and two small deletions were found in the auxotroph sequence, which might explain the branched-chain amino acid auxotrophy. Nevertheless, the leu genes from the auxotroph appear to be transcribed and regulated similarly to those from the prototroph.

Amino Acid Sequence↗
PubMed1993

Gene inactivation in Lactococcus lactis: histidine biosynthesis.

Lactococcus lactis strains from dairy and nondairy sources were tested for the ability to grow in the absence of histidine. Among 60 dairy strains tested, 56 required histidine, whereas only 1 of 11 nondairy strains had this requirement. Moreover, 10 of the 56 auxotrophic strains were able to grow in the presence of histidinol (Hol+), the immediate histidine precursor. This indicates that adaptation to milk often results in histidine auxotrophy. The histidine operon was detected by Southern hybridization in eight dairy auxotrophic strains tested. A large part of the histidine operon (8 kb, containing seven histidine biosynthetic genes and three unrelated open reading frames [ORFs]) was cloned from an auxotroph, which had an inactive hisD gene, as judged by its inability to grow on histidinol. Complementation analysis of three genes, hisA, hisB, and hisG, in Escherichia coli showed that they also were inactive. Sequence analysis of the cloned histidine region, which revealed 98.6% overall homology with that of the previously analyzed prototrophic strain, showed the presence of frameshift mutations in three his genes, hisC, hisG, and hisH, and two genes unrelated to histidine biosynthesis, ORF3 and ORF6. In addition, several mutations were detected in the promoter region of the operon. Northern (RNA) hybridization analysis showed a much lower amount of the his transcript in the auxotrophic strain than in the prototrophic strain. The mutations detected account for the histidine auxotrophy of the analyzed strain. Certain other dairy auxotrophic strains carry a lower number of mutations, since they were able to revert either to a Hol+ phenotype or to histidine prototrophy.

Amino Acid Sequence↗
PubMed1992

Histidine biosynthesis genes in Lactococcus lactis subsp. lactis.

The genes of Lactococcus lactis subsp. lactis involved in histidine biosynthesis were cloned and characterized by complementation of Escherichia coli and Bacillus subtilis mutants and DNA sequencing. Complementation of E. coli hisA, hisB, hisC, hisD, hisF, hisG, and hisIE genes and the B. subtilis hisH gene (the E. coli hisC equivalent) allowed localization of the corresponding lactococcal genes. Nucleotide sequence analysis of the 11.5-kb lactococcal region revealed 14 open reading frames (ORFs), 12 of which might form an operon. The putative operon includes eight ORFs which encode proteins homologous to enzymes involved in histidine biosynthesis. The operon also contains (i) an ORF encoding a protein homologous to the histidyl-tRNA synthetases but lacking a motif implicated in synthetase activity, which suggests that it has a role different from tRNA aminoacylation, and (ii) an ORF encoding a protein that is homologous to the 3'-aminoglycoside phosphotransferases but does not confer antibiotic resistance. The remaining ORFs specify products which have no homology with proteins in the EMBL and GenBank data bases.

Amino Acid Sequence↗
PubMed1990

[Multiple agenesis and prosthetic restoration].

Cases of multiple agenesia present some difficulties in the treatment planing. Three situations may be encountered: limited agenesia, restored by a fixed, bonded or cemented prosthesis, multiple uni- or bimaxillary agenesia without remaining of deciduous teeth, restored by a fixed, bonded or cemented prosthesis or the partial adjacent prosthesis, multiple uni- or bimaxillary agenesia with remaining of deciduous teeth, restored by means of a supra-dental prosthesis. The first two situations have been described in dental literature and are relatively easy to treat. The same is not true for the third situation, where the decision to keep the temporary teeth considerably increases the difficulty of prosthetic restoration. This subject will be illustrated by the presentation of a clinical case of multiple bi-maxillary agenesia. The patient has: on the maxilla: an absence of 9 permanent teeth (18, 15, 14, 12, 22, 23, 24, 25, 28) and the presence of 4 deciduous teeth (62, 63, 64, 65), on the mandible: an absence of all permanent teeth, with the exception of 36 and 46, and the remaining of 4 deciduous teeth (75, 73, 83, 84). The remaining of deciduous teeth and the presence of a very high inter-arch space led to opting for dental coverage so as to keep the deciduous teeth and a proper vertical dimension. The patient wished to solve his "problem" in the maxilla first, and is not wanting to undergo the extraction of his deciduous teeth. The following therapeutic proposal was adapted: On the maxilla, a three-step procedure: first step: building of metal copings on 13, 16 and 26 and metal-ceramic crowns on 11 and 21, second step: building of telescop crowns on 16 and 26 and clasps on 13, 11 and 21, third step: casting of the removable partial denture framework and soldering to the telescop crowns and clasps. On the mandible, a provisional restoration using a supra-dental resin removable partial denture with ceramic occlusal surfaces was adopted. The aesthetic and functional improvement, as well as the comfort provided to the patient due to this kind of mixed prosthesis, appeared to be satisfactory.

Adult↗
PubMed1989

Product of the Lactococcus lactis gene required for malolactic fermentation is homologous to a family of positive regulators.

Malolactic fermentation is a secondary fermentation that many lactic acid bacteria can carry out when L-malate is present in the medium. The activation of the malolactic system in Lactococcus lactis is mediated by a locus we call mleR. Induction of the genes necessary to perform malolactic fermentation occurs only in bacteria with a functional copy of mleR. The mleR gene consists of one open reading frame capable of coding for a protein with a calculated molecular mass of 33,813 daltons. The amino acid sequence of the predicted MleR gene product is homologous to that of positive activators in gram-negative bacteria: LysR, IlvY gene products of Escherichia coli, MetR, CysB of Salmonella typhimurium, AmpR of Enterobacter cloacae, NodD of Rhizobium sp., and TrpI of Pseudomonas aeruginosa.

Amino Acid Sequence↗
PubMed1988

Role of malolactic fermentation in lactic acid bacteria.

Although decarboxylation of malate to lactate by malolactic enzyme does not liberate biologically available energy (e.g., ATP, NADH), the growth rate of many malolactic bacteria is greatly enhanced by malolactic fermentation. The deacidification of the medium due to malate dissipation cannot fully account for this situation. The chemiosmotic theory postulates that another form of energy could generated by translocation of protons through the membrane coupled to end-product efflux. Konings et al. showed that this theory is indeed applicable to lactate efflux in Streptococcus cremoris at pH 7.0. A similar mechanism could account for the observed increased activity in malolactic bacteria. The study in wild type and mutant strains of Streptococcus lactis unable to carry out malolactic fermentation led us to the following conclusions: (1) under glucose non-limiting conditions, malolactic fermentation helps to maintain pH of the medium at a certain level; (2) during glucose limited growth, malolactic fermentation could be coupled with an energetic process independent from that mentioned above.

Energy Transfer↗
PubMed1988

[Malignant non-Hodgkin's lymphoma of tracheo-bronchial sites].

The case of a 66 years old male patient with multiple tracheal and bronchial lesions of non-Hodgkin lymphoma is reported. This was a disseminated form of low-malignancy lymphoma, as shown by histological findings. The lesions disappeared after 10 courses of chemotherapy, and no sign of recurrence was observed during a 3 years' follow-up. It is concluded that the prognosis of this disease depends on histology rather than on anatomical spread.

Aged↗
PubMed1986

Bronchoscopic cryotherapy for airway strictures caused by tumors.

This study reports an application of cryosurgery for the treatment of tracheobronchial tumors. Bronchoscopic cryotherapy can be applied in patients who are not candidates for other traditional therapy. The technique utilizes a nitrous oxide cryoprobe, introduced through a rigid bronchoscope. The principal feature of this probe is to be nonrigid. The cryodestruction is controlled by an impedance metric method. The study group consisted of 27 patients ranging in age from 39 to 88 years. The most frequent diagnosis was squamous cell carcinoma (14). For malignant tumors, the objective was obtained in 13 cases out of 21. Cryotherapy successfully destroyed five benign granulomas. Four or six days after cryotherapy, bronchial biopsy specimens usually showed a necrotic substance, and tumoral tissues were entirely destroyed. The time of survival is probably extended and the quality of life bettered. Most visible tumors are now reached with a flexible cryoprobe, inserted in a flexible bronchoscope.

Adenocarcinoma↗
PubMed1985

Fluorescence as a guide to bronchial biopsy.

The presence of fluorescence was assessed in 34 unselected patients undergoing bronchoscopy, 11 of whom suffered from bronchial carcinoma. Bronchoscopic inspection was carried out with white light and then repeated with blue light after the injection of 2 ml of 10% sodium fluoresceinate. Fluorescence was graded visually. Seventy six pairs of biopsy specimens were obtained. Of 38 specimens from non fluorescent areas, histological appearances were normal in 34. Slight inflammation was observed in three biopsy specimens, and in one there was evidence of tumour even though the specimen was obtained some distance from the primary tumour. Of 38 biopsy specimens from fluorescent areas, histological examination showed appearances of moderate inflammation in 10, severe inflammation in 10, tuberculosis in one, and carcinoma in 11. In six instances histological appearances were normal. Five normal subjects who were smokers were also examined by the same technique. Appearances of metaplasia were found more often in areas showing fluorescence than in areas not showing fluorescence. Bronchial fluorescence is considered to be related to alteration in vascularity and is not specific for carcinoma. The most fluorescent areas are generally the most pathological and visible tumour is very fluorescent, but moderate degrees of fluorescence are difficult to interpret. Biopsy of every fluorescent area seems excessive.

Adult↗
PubMed1985

[Anatomopathology, physiopathology and treatment of the emphysematous disease of infants (apropos of an experience with 133 surgically treated cases)].

Infantile and childhood lobar pulmonary emphysema (LPE) has finally become a rather straightforward problem after 28 years experience and the important statistics published. Contrary to adult emphysema, and leaving aside the particular aspects of causal lesions, the pediatric form is usually a unilateral lobar or infralobar disorder, and therefore lends itself to surgical treatment.

Adolescent↗