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PubMed2002

Microdosimetric one hit detector model for calculation of dose and energy response of some solid state detectors.

A microdosimetric one hit detector model has been applied to calculate dose response, energy response and relative efficiency of thermoluminescent LiF:Mg,Cu,P (MCP-N), CaF2:Tm (TLD-300) and ESR alanine detectors on radiation of different qualities. For each detector type two model parameters, the target size and the saturation parameter, alpha, have been derived. Using those parameters and the microdosimetric distributions in nanometre size targets calculated using Monte Carlo track structure codes TRION and MOCA-14 it was possible to predict a great variety of experimental data for photons, X rays, beta electrons, protons, alpha particles and heavy ions. Due to a good reproducibility of experimental data some solid state detectors might be useful to test biophysical models of radiation action. Furthermore, these models can give some insight into the physics of radiation action in solid state detectors such as the range of charge interaction, energy levels etc.

Luminescent Measurements↗

PubMed1998

A model for the catabolism of rhizopine in Rhizobium leguminosarum involves a ferredoxin oxygenase complex and the inositol degradative pathway.

Rhizopines are nodule-specific compounds that confer an intraspecies competitive nodulation advantage to strains that can catabolize them. The rhizopine (3-O-methyl-scyllo-inosamine, 3-O-MSI) catabolic moc gene cluster mocCABRDE(F) in Rhizobium leguminosarum bv. viciae strain 1a is located on the Sym plasmid. MocCABR are homologous to the mocCABR gene products from Sinorhizobium meliloti. MocD and MocE contain motifs corresponding to a TOL-like oxygenase and a [2Fe-2S] Rieske-like ferredoxin, respectively. The mocF gene encodes a ferredoxin reductase that would complete the oxygenase system, but is not essential for rhizopine catabolism. We propose a rhizopine catabolic model whereby MocB transports rhizopine into the cell and MocDE and MocF (or a similar protein elsewhere in the genome), under the regulation of MocR, act in concert to form a ferredoxin oxygenase system that demethylates 3-O-MSI to form scyllo-inosamine (SI). MocA, an NAD(H)-dependent dehydrogenase, and MocC continue the catabolic process. Compounds formed then enter the inositol catabolic pathway.

Amino Acid Sequence↗

PubMed1998

Detection and isolation of novel rhizopine-catabolizing bacteria from the environment

Microbial rhizopine-catabolizing (Moc) activity was detected in serial dilutions of soil and rhizosphere washes. The activity observed generally ranged between 10(6) and 10(7) catabolic units per g, and the numbers of nonspecific culture-forming units were found to be approximately 10 times higher. A diverse set of 37 isolates was obtained by enrichment on scyllo-inosamine-containing media. However, none of the bacteria that were isolated were found to contain DNA sequences homologous to the known mocA, mocB, and mocC genes of Sinorhizobium meliloti L5-30. Twenty-one of the isolates could utilize an SI preparation as the sole carbon and nitrogen source for growth. Partial sequencing of 16S ribosomal DNAs (rDNAs) amplified from these strains indicated that five distinct bacterial genera (Arthrobacter, Sinorhizobium, Pseudomonas, Aeromonas, and Alcaligenes) were represented in this set. Only 6 of these 21 isolates could catabolize 3-O-methyl-scyllo-inosamine under standard assay conditions. Two of these, strains D1 and R3, were found to have 16S rDNA sequences very similar to those of Sinorhizobium meliloti. However, these strains are not symbiotically effective on Medicago sativa, and DNA sequences homologous to the nodB and nodC genes were not detected in strains D1 and R3 by Southern hybridization analysis.

Journal Article↗

PubMed1996

Ti plasmid-encoded genes responsible for catabolism of the crown gall opine mannopine by Agrobacterium tumefaciens are homologs of the T-region genes responsible for synthesis of this opine by the plant tumor.

Agrobacterium tumefaciens NT1 harboring pSaB4, which contains the 14-kb BamHI fragment 4 from the octopine/mannityl opine-type Ti plasmid pTi15955, grew well with agropine (AGR) but slowly with mannopine (MOP) as the sole carbon source. When a second plasmid encoding a dedicated transport system for MOP was introduced, these cells grew well with both AGR and MOP. Transposon insertion mutagenesis and subcloning identified a 5.7-kb region of BamHI fragment 4 that encodes functions required for the degradation of MOP. DNA sequence analysis revealed seven putative genes in this region: mocD (moc for mannityl opine catabolism) and mocE, oriented from right to left, and mocRCBAS, oriented from left to right. Significant identities exist at the nucleotide and derived amino acid sequence levels between these moc genes and the mas genes that are responsible for opine biosynthesis in crown gall tumors. MocD is a homolog of Mas2, the anabolic conjugase encoded by mas2'. MocE and MocC are related to the amino half and the carboxyl half, respectively, of Mas1 (MOP reductase), the second enzyme for MOP biosynthesis. These results indicate that the moc and mas genes evolved from a common origin. MocR and MocS are related to each other and to a putative repressor for the AGR degradation system encoded by the rhizogenic plasmid pRiA4. MocB and MocA are homologs of 6-phosphogluconate dehydratase and glucose-6-phosphate dehydrogenase, respectively. Mutations in mocD and mocE, but not mocC, are suppressed by functions encoded by the chromosome or the 450-kb megaplasmid present in many Agrobacterium isolates. We propose that moc genes derived from genes located elsewhere in the bacterial genome and that the tumor-expressed mas genes evolved from the bacterial moc genes.

Agrobacterium tumefaciens↗

PubMed2001

A functional myo-inositol dehydrogenase gene is required for efficient nitrogen fixation and competitiveness of Sinorhizobium fredii USDA191 to nodulate soybean (Glycine max [L.] Merr.).

Inositol derivative compounds provide a nutrient source for soil bacteria that possess the ability to degrade such compounds. Rhizobium strains that are capable of utilizing certain inositol derivatives are better colonizers of their host plants. We have cloned and determined the nucleotide sequence of the myo-inositol dehydrogenase gene (idhA) of Sinorhizobium fredii USDA191, the first enzyme responsible for inositol catabolism. The deduced IdhA protein has a molecular mass of 34,648 Da and shows significant sequence similarity with protein sequences of Sinorhizobium meliloti IdhA and MocA; Bacillus subtilis IolG, YrbE, and YucG; and Streptomyces griseus StrI. S. fredii USDA191 idhA mutants revealed no detectable myo-inositol dehydrogenase activity and failed to grow on myo-inositol as a sole carbon source. Northern blot analysis and idhA-lacZ fusion expression studies indicate that idhA is inducible by myo-inositol. S. fredii USDA191 idhA mutant was drastically affected in its ability to reduce nitrogen and revealed deteriorating bacteroids inside the nodules. The number of bacteria recovered from such nodules was about threefold lower than the number of bacteria isolated from nodules initiated by S. fredii USDA191. In addition, the idhA mutant was also severely affected in its ability to compete with the wild-type strain in nodulating soybean. Under competitive conditions, nodules induced on soybean roots were predominantly occupied by the parent strain, even when the idhA mutant was applied at a 10-fold numerical advantage. Thus, we conclude that a functional idhA gene is required for efficient nitrogen fixation and for competitive nodulation of soybeans by S. fredii USDA191.

Amino Acid Sequence↗

PubMed2002

Isolation and characterization of cLV25, a Bacteroides fragilis chromosomal transfer factor resembling multiple Bacteroides sp. mobilizable transposons.

Horizontal DNA transfer contributes significantly to the dissemination of antibiotic resistance genes in Bacteroides fragilis. To further our understanding of DNA transfer in B. fragilis, we isolated and characterized a new transfer factor, cLV25. cLV25 was isolated from B. fragilis LV25 by its capture on the nonmobilizable Escherichia coli-Bacteroides shuttle vector pGAT400DeltaBglII. Similar to other Bacteroides sp. transfer factors, cLV25 was mobilized in E. coli by the conjugative plasmid R751. Using Tn1000 mutagenesis and deletion analysis of cLV25, two mobilization genes, bmgA and bmgB, were identified, whose predicted proteins have similarity to DNA relaxases and mobilization proteins, respectively. In particular, BmgA and BmgB were homologous to MocA and MocB, respectively, the two mobilization proteins of the B. fragilis mobilizable transposon Tn4399. A cis-acting origin of transfer (oriT) was localized to a 353-bp region that included nearly all of the intergenic region between bmgB and orf22 and overlapped with the 3' end of orf22. This oriT contained a putative nic site sequence but showed no significant similarity to the oriT regions of other transfer factors, including Tn4399. Despite the lack of sequence similarity between the oriTs of cLV25 and Tn4399, a mutation in the cLV25 putative DNA relaxase, bmgA, was partially complemented by Tn4399. In addition to the functional cross-reaction with Tn4399, a second distinguishing feature of cLV25 is that predicted proteins have similarity to proteins encoded not only by Tn4399 but by several Bacteroides sp. transfer factors, including NBU1, NBU2, CTnDOT, Tn4555, and Tn5520.

Bacteroides fragilis↗

PubMed1985

Comparative usefulness of tissue fixatives for in situ viral nucleic acid hybridization.

Traditionally tissues for in situ hybridization of viral nucleic acid have been small pieces obtained from laboratory rodents, and fixatives that are designed for electron microscopy, such as periodate-lysine-paraformaldehyde (PLP) can handle them adequately. However, these fixatives have limited penetrating ability and may produce no appreciable hardening, so alternative fixation methods were evaluated. The intention was to determine whether fixatives adequate for bulky tissues such as whole or halved pig and cow brains would also be compatible with in situ hybridization. Various fixatives were evaluated using a system of intracranial inoculation of BALB/c mice with pseudorabies virus (PRV) followed by in situ hybridization of brain tissue sections with a 35S-labeled PRV DNA probe. Loss of tissue sections was a major problem, particularly with PLP and formalin, but positive results were obtained with five fixatives tested. Cellular morphology was especially good with PLP and with a modification of Carnoy's fluid, MOCA fixative. An incidental but important observation was that formalin is compatible with in situ hybridization. Retroactive studies of viral diseases using routinely processed blocks of tissue (formalin-fixed, paraffin-embedded) are therefore conceivable.

Acetates↗

PubMed2002

Modeling the response of thermoluminescence detectors exposed to low- and high-LET radiation fields.

Lithium fluoride thermoluminescence (TL) detectors, with different Li composition (Li-6 and Li-7) and various activators (LiF:Mg,Ti, LiF:Mg,Cu,P), are widely used for dosimetry in space. The primary radiation field in space is composed of fast electrons, protons and heavy charged particles (HCP). By its interaction with the structures of the spacecraft, this field may be modified inside the crew cabin. Therefore, calibration of TL detectors against a dose of gamma-rays is not sufficient for relating the TL readout to absorbed dose or to quantities relevant in radiation protection, without suitable correction. We introduce and calculate the detection efficiency, eta, relative to gamma-ray dose, of lithium fluoride detectors after proton and heavy charged particle (HCP) irradiation. We calculate eta for MCP-N (LiF:Mg,Cu,P) and for MTS-N (LiF:Mg,Ti) using microdosimetric models. The microdosimetric distributions used in these models (for HCP of charges between Z=1 to Z=8 and in the energy range between 0.3 MeV/amu and 20 MeV/amu) are calculated using an analytical model, based on the results of Monte Carlo simulated charged particle tracks using the MOCA-14 code. The ratio etaMCP-N/etaMTS-N for protons of stopping power (in water) below 10 keV/microm lies in the range between 0.65 and 1.0 and for HCP with Z>1--between 0.3 and 0.6. The stopping power of the particle is found not to be a unique parameter to scale the response of TL detectors. The combination of response of LiF:Mg,Cu,P and LiF:Mg,Cu,P detectors can be more suitable for a dose correction in space radiation fields.

Computer Simulation↗

PubMed1986

[Prevention of occupational carcinogens: perspectives opened by the evaluation of risks and preventive actions].

The first part of the review deals with the present situation in terms of prevention against potential carcinogenic substances in France. A significant effort should be devoted to the measurement of contaminants--not only carcinogenic substances--in the workplace. This is a prerequisite for setting a data base in terms of potential occupational risk. Moreover gaps exist also as far as the definition of the technical means aimed at the reduction of risk is concerned. These conclusions put into light the importance of the contribution that "industrial hygienists" would bring in France. In the second part of the review, the methodological content of the risk assessment and risk management procedures is described and illustrated. Risk assessment of carcinogens deals: with the identification of potential carcinogens through epidemiology, animal bio-assays and short term tests; with the quantitative estimation of the magnitude of the potential carcinogenic risk among the exposed workers. It appears necessary to carry out systematic surveys of the number of workers exposed to the carcinogenic substances. The risk assessment procedure is applied to 5 substances BCME, MOCA, Acrylonitrile, Chromium, Nickel and some compounds of these metals. The number of potential excess cancers related to a unit lifelong exposure to Nickel compounds is estimated. This requires exposure-response models which are critically analysed. Risk management is devoted to the choice of primary health care policies. The methodology of risk management consists of: identifying various control policies; quantitative estimation of their efficiency--indicators of the efficiency are discussed--and of their cost; choice among these policies with the help of a cost-effectiveness analysis when necessary. The procedure is illustrated in the case of Acrylonitrile control in a facility.

Carcinogens↗

PubMed1977

[Gastro-intestinal involvement in non Hodgkin's lymphomas, 31 cases (author's transl)].

Gastro-intestinal involvement is a distinctive feature of non-Hodgkin's lymphomas. 31 cases are reported among 200 cases on NHL observed between 1960 and 1976. Multiple involvement appeared in 61%; a diffuse histological pattern is frequent (67%). The relapse of primary isolated gastro-intestinal localization (always) affected extra-digestive tissues (nodes, cavum). Chemotherapy is the mainstay of treatment COP, COAP and MOCA. Surgery is associated in localized involvement or in case of obstruction. High energy radiation therapy is indicated only in lymphosarcomas: -- to residual tumor after chemotherapy--in localized involvement diffuse on all the abdomen at 25 grays after surgery and a brief course of chemotherapy versus surgery and long course of chemotherapy alone.

Drug Therapy, Combination↗

PubMed1995

[Gestational trophoblastic tumors--a report of experiences].

The paper reports on clinical experiences of treatment of 58 patients with Gestational Trophoblastic Tumors (GTT), collected between 1978 and 1991. According to the Bagshawe-Score, 29 patients were at low-risk, 10 patients were assigned to the high-risk category. Among 29 metastatic cases, 5 patients had brain metastasis. In 33 patients, treatment started from the time of diagnosis. In 25 cases, treatment was initiated at other hospitals and patients were referred only after various unsatisfactory treatment measures. Low-risk patients were mainly subjected to methotrexate and folinic acid. Patients at medium-risk received a sequential chemotherapy. In high-risk patients we preferred the CHA-MOCA- or the EMA/CO-regimen. Treatment was successful in 91.4% of patients including all cases of low- and medium-risk. Five patients with brain metastases received systemic chemotherapy combined with intrathecal application of methotrexate and radiotherapy. Three of them could be cured. Patients taken from other hospitals more often underwent primary hysterectomies prior to systemic chemotherapy (40% versus 3%) and more often developed drug resistant tumors due to inadequate primary treatment. Five patients (8.6%) died from their disease, but only one of them received primary treatment in our department. Thus, the outcome (1/33 compared to 4/25) was significantly better for patients treated primarily at specialized centers.

Adult↗

PubMed2005