Dosimetric evaluation of a spinal cord dose-limiting 3D-CRT technique for radiotherapy of spinal metastases

BACKGROUND

To evaluate the possible advantages of a simple spinal cord (SC) dose-limiting three-dimensional conformal radiotherapy (3D-CRT) technique in comparison to conventional two-dimensional (2D) techniques and other 3D-CRT techniques for spinal bone irradiation.

METHODS

For 41 spinal target volumes, seven different techniques were evaluated, using a standard schedule of 30 Gy in 10 fractions. The SC dose-limiting 3D-CRT technique 1F2S-18MV using a single posterior field (F) supplemented by two anterior segment fields (S) and 18-MV photon beams was compared to two conventional 2D techniques (a single posterior field, PA, and two opposed anterior-posterior fields, APPA), three other 3D-CRT techniques (a single posterior field supplemented by four segment fields, 1F4S; two wedged fields, WD, and the SC dose-limiting variant using 6 MV, 1F2S-6MV) along with the original clinically applied plans.

RESULTS

1F2S-18MV demonstrated notably better results for all target volume parameters compared to the conventional 2D techniques (p < 0.001). Limitation of the SC dose was significantly superior with 1F2S-18MV in comparison to PA and APPA (SC Dmean: 28.9 ± 0.4  vs. 30.1 ± 0.6 Gy and 30.1 ± 0.4 Gy; SC Dmax: 30.9 ± 0.7  vs. 32.5 ± 1.0 Gy and 31.8 ± 0.7 Gy; SC D1cm3 : 30.1 ± 0.6  vs. 31.7 ± 0.9 Gy and 31.1 ± 0.6 Gy; p < 0.001). Likewise, lower mean SC doses with 1F2S-18MV were observed in comparison to the more treatment time-consuming 3D-CRT techniques (1F4S, WD) and the original plans without relevant compromises on the dose homogeneity in the target volume and the dose exposure to the other OARs.

CONCLUSION

In treatment planning of spinal metastases, simple variants of 3D-CRT-techniques like 1F2S-18MV can offer a significant dose limitation to the SC while providing a sufficient dose coverage of the target volume. Especially in patients with favorable life expectancy and potential need for re-irradiation, such SC dose-limiting 3D-CRT techniques may be a reasonable approach.

Dosimetric Evaluation of Commercially Available Flat vs. Self-Produced 3D-Conformal Silicone Boluses for the Head and Neck Region

Background

Boluses are routinely used in radiotherapy to modify surface doses. Nevertheless, considerable dose discrepancies may occur in some cases due to fit inaccuracy of commercially available standard flat boluses. Moreover, due to the simple geometric design of conventional boluses, also surrounding healthy skin areas may be unintentionally covered, resulting in the unwanted dose buildup. With the fused deposition modeling (FDM) technique, there is a simple and possibly cost-effective way to solve these problems in routine clinical practice. This paper presents a procedure of self-manufacturing bespoke patient-specific silicone boluses and the evaluation of buildup and fit accuracy in comparison to standard rectangular commercially available silicone boluses.

Methods

3D-conformal silicone boluses were custom-built to cover the surgical scar region of 25 patients who received adjuvant radiotherapy of head and neck cancer at the University Hospital Würzburg. During a standard CT-based planning procedure, a 5-mm-thick 3D bolus contour was generated to cover the radiopaque marked surgical scar with an additional safety margin. From these digital contours, molds were 3D printed and poured with silicone. Dose measurements for both types of boluses were performed with radiochromic films (EBT3) at three points per patient—at least one aimed to be in the high-dose area (scar) and one in the lower-dose area (spared healthy skin). Surface–bolus distance, which ideally should not be present, was determined from cone-beam CT performed for positioning control. The dosimetric influence of surface–bolus distance was also determined on slab phantom for different field sizes. The trial was performed with hardware that may be routinely available in every radiotherapy department, with the exception of the 3D printer. The required number of patients was determined based on the results of preparatory measurements with the help of the statistical consultancy of the University of Würzburg. The number of measuring points represents the total number of patients.

Results

In the high-dose area of the scar, there was a significantly better intended dose buildup of 2.45% (95%CI 0.0014–0.0477, p = 0.038, N = 30) in favor of a 3D-conformal bolus. Median distances between the body surface and bolus differed significantly between 3D-conformal and commercially available boluses (3.5 vs. 7.9 mm, p = 0.001). The surface dose at the slab phantom did not differ between commercially available and 3D-conformal boluses. Increasing the surface–bolus distance from 5 to 10 mm decreased the surface dose by approximately 2% and 11% in the 6 × 6- and 3 × 3-cm² fields, respectively. In comparison to the commercially available bolus, an unintended dose buildup in the healthy skin areas was reduced by 25.9% (95%CI 19.5–32.3, p < 0.01, N = 37) using the 3D-conformal bolus limited to the region surrounding the surgical scar.

Conclusions

Using 3D-conformal boluses allows a comparison to the commercially available boluses’ dose buildup in the covered areas. Smaller field size is prone to a larger surface–bolus distance effect. Higher conformity of 3D-conformal boluses reduces this effect. This may be especially relevant for volumetric modulated arc therapy (VMAT) and intensity-modulated radiotherapy (IMRT) techniques with a huge number of smaller fields. High conformity of 3D-conformal boluses reduces an unintended dose buildup in healthy skin. The limiting factor in the conformity of 3D-conformal boluses in our setting was the immobilization mask, which was produced primarily for the 3D boluses. The mask itself limited tight contact of subsequently produced 3D-conformal boluses to the mask-covered body areas. In this respect, bolus adjustment before mask fabrication will be done in the future setting.

Risk factors for vertebral compression fracture after spine stereotactic body radiation therapy: Long-term results of a prospective phase 2 study

PURPOSE

To identify frequency, clinical relevance and risk factors for vertebral compression fracture (VCF) after spine stereotactic body radiation therapy (SBRT) with long-term follow up (FU).

METHODS

From 2012 to 2015, 61 lesions (56 patients) were treated within a prospective multicenter phase 2 study (NCT01594892) of SBRT for painful vertebral metastases. Post-SBRT VCF were identified. Anatomical segments, normal and tumor tissue of treated vertebrae were segmented for volumetric analyses. Predictive factors for VCF were identified by logistic regression.

RESULTS

Median clinical and radiological FU for all patients was 16.2 months (range, 0-68.2) and 7.8 months (range, 0-66.9), respectively. Local metastasis control was observed in 82% of lesions at last imaging FU. Post-SBRT VCF occurred in 21 lesions (34.4%): 16.4% showed a progressive VCF, while a new VCF occurred in 18.0%. 3/56 (5.4%) patients developed painful VCF defined as pain increase by ≥2 on the visual analogue scale (VAS) and 2 (3.6%) patients required surgical stabilization. Pre-SBRT VCF, localization in the thoracic spine, Bilsky score >0, SINS score, pre-SBRT osteolytic volume and metastatic vertebral body (VB) involvement were predictive factors for VCF on univariate analysis. Relative VB involvement, osteolytic volume and pre-SBRT VCF remained in the multivariate logistic regression model that had AUC = 0.930, 83.3% sensitivity and 96.6% specificity.

CONCLUSION

Spine SBRT resulted in favorable long-term pain and local metastasis control. Despite post-SBRT VCF being observed after one third of treatments, this was symptomatic in only 5% of patients. Predictive factors for developing VCF were identified which could contribute to better selection of patients for spine SBRT.

Abstract P6-16-02: Fertility preservation in young breast cancer patients: Real life data on 1390 patients treated in the Institut Curie

Introduction: Adverse effects of chemotherapy on fertility are a critical concern for young breast cancer (BC) patients. Fertility preservation (FP) is currently offered to BC patients, though literature data concerning reproductive outcomes are scarce. Also, very few data are available on whether these procedures are associated with delay to treatment, or whether they impact oncologic outcomes. The objective of our study is to evaluate: (i) efficacy of FP procedures in terms of stored material and pregnancy rates, (ii) safety regarding time from BC diagnosis to chemotherapy, and oncologic outcomes in a large real-life cohort of BC patients.

Methods: We retrospectively analyzed medical charts of all consecutive patients aged between 18 and 43 diagnosed with invasive BC between 01/01/2011 and 30/09/2017 and treated with chemotherapy at Institut Curie (Paris and Saint Cloud). Baseline factors (antral follicle count (AFC), AMH), details on fertility preservation procedures, and results (number of frozen oocytes and embryos) were retrieved in 3 academic hospitals (Jean Verdier, Antoine Béclère and Cochin). All medical charts were reviewed in March 2018 to assess time from diagnosis to surgery / chemotherapy, pregnancy outcomes, recurrence and survival. We compared time from first consultation to start of chemotherapy (time diagnosis-to-CT) in case of neoadjuvant chemotherapy (NAC between patients who had or who did not have PF.

Results: On 1.390 patients identified, 622 had NAC, 768 had adjuvant CT. Median age at diagnosis was 38.8 y.o. 136 were BRCA mutated.

- 264 patients (19%) underwent a FP procedure: In Vitro Maturation (IVM) (58%, n=154); ovarian stimulation protocol (STIM) (31%, n=82); others (10%, n=28). The mean number of oocytes preserved was 5 [0-36] and was not different between IMV and STIM.

- Delays from diagnosis to CT were not different in patients who had FP than those who did not, neither in patients with NAC (no FP: 24.1 days VS FP: 22.8, p=0.24) nor in patients with adjuvant CT (no FP: 70.6 days VS FP : 66.8, p=0.11).

- 39 patients had at least one pregnancy: 28 spontaneous, 6 without information, and 5 from oocyte/embryo donation. The pregnancy rate was higher in patients in FP group (n=16 ; 6%) than in no FP group (n=23 ; 2%). 3 reused material : 2 without pregnancy and one had a miscarriage.

- About oncologic outcomes, 90 patients underwent relapse (6,4%), and this rate was not significantly different in the 2 groups (n=12, 4,5% VS n=78, 6.9%).

- Patients with BRCA mutation (BRCAm) had lower AMH (2.9 VS 4.1 ng/mL ; p = 0,03) and antral follicle count (17.6 VS 24 ; p = 0.01). However, there was no difference on the stored material, and pregnancy rate was higher than in patients with no mutation or unkwnown status (7.6 VS 2.6% ; p = 0,01).

Conclusion: Pregnancy rate was higher in patients with FP, however majority of pregnancies was spontaneous, and no live birth was observed after material reuse. FP procedures were not associated with delay to treatment. Though bias cannot be excluded, preliminary data do not show an adverse impact of FP on oncologic outcome. Further follow-up is needed.

Citation Format: Hamy-Petit A-S, Toussaint A, Sautter C, Coussy F, Donnadieu A, Rouzier R, Saule C, Frank S, Bensen A, Grynberg M, Scarabin-Carre V, Santulli P, Balezeau T, Guerin J, Reyrat E, Jamain C, Hours A, Lecourt A, Reyal F. Fertility preservation in young breast cancer patients: Real life data on 1390 patients treated in the Institut Curie [abstract]. In: Proceedings of the 2018 San Antonio Breast Cancer Symposium; 2018 Dec 4-8; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2019;79(4 Suppl):Abstract nr P6-16-02.

Combining NSAM and CPC concentrations to determine airborne nanoparticle count median diameter: Application to various laboratory and workplace aerosols

Because nanomaterials have been increasingly developed and used in many technology and industry sectors over the last 20 years, an increasing number of workers is likely to be exposed to airborne nanoparticles. In addition, the question of the nanomaterial characteristics that should be assessed in epidemiological studies remains open. Thus, assessing occupational exposure to airborne nanoparticles will not only rely on mass concentration and chemical composition. Rather, key parameters, such as particle size, have to be included in measurement strategies. We previously proposed a methodology to estimate the Count Median Diameter (CMD) of an aerosol based on the simultaneous size-integrated measurement of two particle concentrations, lung-deposited surface area, and number, thanks to field-portable, commercially available aerosol instruments (Nanoparticle Surface Area Monitor/Condensation Particle Counter combination). In addition to previous work, this study investigates the case of various polydisperse metal oxides, organic oil, and salt particles with CMDs ranging from 16-410 nm. Once corrected, the CMDs derived from the NSAM/CPC agree within ±20% with regard to the reference electrical mobility equivalent diameter, regardless of aerosol composition, morphology, or geometric standard deviation (GSD). Furthermore, the field-applicability of the method was tested through 6 sets of experimental data stemming from workplace measurement campaigns where different materials were produced and handled (TiO₂, SiO₂, Ag, Multi-Walled Carbon Nanotubes-MWCNT), covering a range of CMDs between 40 and 190 nm. All situations considered, the approach based on the combination of a NSAM and a CPC leads to a satisfying estimation of particle CMD, within ±20% compared to reference CMD.

Variability in spine radiosurgery treatment planning - results of an international multi-institutional study

BACKGROUND

The aim of this study was to quantify the variability in spinal radiosurgery (SRS) planning practices between five international institutions, all member of the Elekta Spine Radiosurgery Research Consortium.

METHODS

Four institutions provided one representative patient case each consisting of the medical history, CT and MR imaging. A step-wise planning approach was used where, after each planning step a consensus was generated that formed the basis for the next planning step. This allowed independent analysis of all planning steps of CT-MR image registration, GTV definition, CTV definition, PTV definition and SRS treatment planning. In addition, each institution generated one additional SRS plan for each case based on intra-institutional image registration and contouring, independent of consensus results.

RESULTS

Averaged over the four cases, image registration variability ranged between translational 1.1 mm and 2.4 mm and rotational 1.1° and 2.0° in all three directions. GTV delineation variability was 1.5 mm in axial and 1.6 mm in longitudinal direction averaged for the four cases. CTV delineation variability was 0.8 mm in axial and 1.2 mm in longitudinal direction. CTV-to-PTV margins ranged between 0 mm and 2 mm according to institutional protocol. Delineation variability was 1 mm in axial directions for the spinal cord. Average PTV coverage for a single fraction18 Gy prescription was 87 ± 5 %; Dmin to the PTV was 7.5 ± 1.8 Gy averaged over all cases and institutions. Average Dmax to the PRV_SC (spinal cord + 1 mm) was 10.5 ± 1.6 Gy and the average Paddick conformity index was 0.69 ± 0.06.

CONCLUSIONS

Results of this study reflect the variability in current practice of spine radiosurgery in large and highly experienced academic centers. Despite close methodical agreement in the daily workflow, clinically significant variability in all steps of the treatment planning process was demonstrated. This may translate into differences in patient clinical outcome and highlights the need for consensus and established delineation and planning criteria.

Global functional diversity of freshwater fish is concentrated in the Neotropics while functional vulnerability is widespread

Worldwide biodiversity assessments have mainly focused on species richness but little is known about the diversity of species roles, i.e. functional diversity, while this is a key facet to understanding the consequences of global changes on the ecosystem services to human societies. Here, we report the world pattern of functional diversity of freshwater fish using a database encompassing morphological characteristics of more than 9,000 species. The Neotropical realm hosts more than 75% of global functional diversity while other realms each host less than 25%. This discrepancy is mediated by high functional uniqueness in some diversified Neotropical fish orders. Surprisingly, functional diversity patterns were weakly related to functional vulnerability. In the Neotropics the loss of threatened species will cause a limited loss of functional diversity (<10%) whereas in the Nearctic and Palearctic realms, decline of the functional diversity will reach 43% and 33%, respectively, conferring a high functional vulnerability to these realms. Conservation of the Neotropical fish diversity is a key target to maintain world fish functional diversity, but this should not hide the pressing need to conserve the vulnerable fish faunas of the rest of the world, in which functional diversity is to a large extent supported by threatened species.

[Management of acute iliac thrombosis in a pregnancy at term: case discussion and review of literature]

Venous thromboembolic disease during pregnancy is an important cause of obstetric morbidity and mortality. Suggestive clinical signs lead systematically physicians to evocate this diagnosis. Unfortunately, the incidence of events remains low, reducing the ability to perform well-designed research and to give adequate recommendations. The discovery in term pregnancy of an iliofemoral venous thrombosis raises the question of obstetrical care, mainly considering potentially embolic risk. Through a case report and based on a thinking about the few medical publications in this field, we suggest that the placing of temporary inferior vena cava filter in presence of an extensive deep venous thrombosis at term pregnancy could be debatable.

Characterization and expression profile analysis of a sucrose synthase gene from common bean (Phaseolus vulgaris L.) during seed development

A full-length cDNA encoding common bean (Phaseolus vulgaris L.) sucrose synthase (designated as Pv_BAT93 Sus), which catalyses the synthesis and cleavage of sucrose, was isolated from seeds at 15 days after pollination (DAP) by rapid amplification of cDNA ends (RACE). The full-length cDNA of Pv_BAT93 Sus had a 2,418 bp open reading frame (ORF) encoding a protein of 806 amino acid residues. Sequence comparison analysis showed that Pv_BAT93 Sus was very similar to several members of the sucrose synthase family of other plant species. Tissue expression pattern analysis showed that Pv_BAT93 Sus was expressed in leaves, flowers, stems, roots, cotyledons, and particularly during seed development. Expression studies using in situ hybridization revealed altered spatial and temporal patterns of Sus expression in the EMS mutant relative to wild-type and confirmed Sus expression in common bean developing seeds. The expression and accumulation of Sus mRNA was clearly shown in several tissues, such as the suspensor and embryo, but also in the transfer cells and endothelium. The results highlight the diverse roles that Sus might play during seed development in common bean.

Role of myo-inositol phosphate synthase and sucrose synthase genes in plant seed development

The aim of this review is to highlight the role of myo-inositol phosphate synthase (MIPS), which catalyses the first step in inositol biosynthesis and of sucrose synthase (Sus), an enzyme involved in UDP-glucose formation, the principal nucleoside diphosphate in the sucrose cleavage reaction and in trehalose biosynthesis. These two enzymes are involved in various physiological processes including seed growth and resistance to biotic and abiotic stresses. The study of mutated MIPS and Sus genes in some crops, such as soybean and cotton, has shown that these two proteins are directly involved in embryogenesis. They exhibit several isoforms that are essential for normal seed development. The possible role of both genes in seed development is discussed in this review.

[Drawing the alcoholic out of his isolation]

Alcohol is by far the most frequent addiction across industrial countries. Associated with unrest, rejection and other negative counter-attitudes, alcohol dependence often confines the patient to isolation. The objective of this article is to describe potential obstacles to access to health care, the strategies enabling this access and finally different programs and therapeutic modalities of a long-term treatment. This article focuses on these issues in term of level of intervention.

Manifestations of hereditary hemorrhagic telangiectasia in children and adolescents

The medical literature provides little information on manifestations of hereditary hemorrhagic telangiectasia (HHT) in children. The presented investigation was initiated to analyze early presenting symptoms in HHT, which should help to make the diagnosis at a young age and thus prevent potential complications from occult visceral arteriovenous malformations (AVM), which have commonly been described in HHT. A series of 15 children and adolescents with a suspicious diagnosis of HHT were examined clinically for typical signs and symptoms of the disorder. If the diagnosis of HHT seemed to be likely, recommendations for non-invasive screening procedures were given. Screening was directed at the detection of occult visceral AVMs. Main outcome measures were the definition of principal signs of HHT in children and adolescents. Family history was positive for HHT in 13 persons. The principal sign of recurrent epistaxis was present in 10/15 individuals and the earliest age of onset with regard to epistaxis was 4 years. Cutaneous vascular lesions were present in 5/15 patients. Screening for AVMs was performed in six individuals and revealed vascular lesions of the brain in two patients and vascular lesions of the lung in two patients. Gastrointestinal hemorrhages were present in one infant. Based on these findings, diagnosis of HHT seemed likely in ten individuals and unlikely in five individuals. Signs and symptoms of HHT in children and adolescents may be discrete, but are detectable at an earlier age than previously thought. Clinical examinations in children from HHT families may help identify candidates who will benefit from molecular genetic testing or screening imaging studies.

Extreme, unilateral widening of Virchow-Robin spaces: case report

We report a case of extreme, largely unilateral dilatation of Virchow-Robin spaces. Fluid-attenuated inversion-recovery images revealed high-signal foci adjacent to the dilated spaces, possibly due to chronic ischaemia.

The tRNA function of SsrA contributes to controlling repression of bacteriophage Mu prophage

The small regulatory RNA SsrA has both tRNA and mRNA activities. It charges alanine and interacts with stalled ribosomes, allowing for translation to resume on the SsrA mRNA moiety. Hence, unfinished peptides carry a short amino acid tag, which serves as a signal for degradation by energy-dependent proteases. In SsrA-defective Escherichia coli strains, thermoinducible mutants of the transposable bacteriophage Mu (Mucts) are no longer induced at high temperature. Here we show that truncated forms of the key regulator of Mu lysogeny, the repressor Repc, accumulate in the absence of SsrA. These forms resemble C-terminally truncated dominant Mu repressor mutants previously isolated from Mucts, which are no longer thermoinducible and bind operator DNA with a high affinity even at high temperature. Using various ssrA alleles, we demonstrate the importance of SsrA charging on the ribosome for controlling Mu prophage repression. Our results thus substantiate the previous observation that trans-translation is not the only function of the SsrA. The alternative function of SsrA appears to influence the stability of Mu lysogens by controlling the translation of the C-terminal domain of the repressor protein, which modulates the affinity of the protein for DNA and its susceptibility to proteolytic degradation.

Ipriflavone in the treatment of postmenopausal osteoporosis: a randomized controlled trial

CONTEXT

Data on the efficacy and safety of ipriflavone for prevention of postmenopausal bone loss are conflicting.

OBJECTIVES

To investigate the effect of oral ipriflavone on prevention of postmenopausal bone loss and to assess the safety profile of long-term treatment with ipriflavone in postmenopausal osteoporotic women.

DESIGN AND SETTING

Prospective, randomized, double-blind, placebo-controlled, 4-year study conducted in 4 centers in Belgium, Denmark, and Italy from August 1994 to July 1998.

PARTICIPANTS

Four hundred seventy-four postmenopausal white women, aged 45 to 75 years, with bone mineral densities (BMDs) of less than 0.86 g/cm(2).

INTERVENTIONS

Patients were randomly assigned to receive ipriflavone, 200 mg 3 times per day (n = 234), or placebo (n = 240); all received 500 mg/d of calcium.

MAIN OUTCOME MEASURES

Efficacy measures included spine, hip, and forearm BMD and biochemical markers of bone resorption (urinary hydroxyproline corrected for creatinine and urinary CrossLaps [Osteometer Biotech, Herlev, Denmark] corrected for creatinine), assessed every 6 months. Laboratory safety measures and adverse events were recorded every 3 months.

RESULTS

Based on intent-to-treat analysis, after 36 months of treatment, the annual percentage change from baseline in BMD of the lumbar spine for ipriflavone vs placebo (0.1% [95% confidence interval (CI), -7.9% to 8.1%] vs 0.8% [95% CI, -9.1% to 10.7%]; P =.14), or in any of the other sites measured, did not differ significantly between groups. The response in biochemical markers was also similar between groups (eg, for hydroxyproline corrected for creatinine, 20.13 mg/g [95% CI, 18.85-21.41 mg/g] vs 20.67 mg/g [95% CI, 19.41-21.92 mg/g]; P =.96); urinary CrossLaps corrected for creatinine, 268 mg/mol (95% CI, 249-288 mg/mol) vs 268 mg/mol (95% CI, 254-282 mg/mol); P =.81. The number of women with new vertebral fracture was identical or nearly so in the 2 groups at all time points. Lymphocyte concentrations decreased significantly (500/microL (0.5 x 10(9)/L]) in women treated with ipriflavone. Thirty-one women (13.2%) in the ipriflavone group developed subclinical lymphocytopenia, of whom 29 developed it during ipriflavone treatment. Of these, 15 (52%) of 29 had recovered spontaneously by 1 year and 22 (81%) of 29 by 2 years.

CONCLUSIONS

Our data indicate that ipriflavone does not prevent bone loss or affect biochemical markers of bone metabolism. Additionally, ipriflavone induces lymphocytopenia in a significant number of women.

Occurrence of Tn4371-related mobile elements and sequences in (chloro)biphenyl-degrading bacteria

Tn4371, a 55-kb transposable element involved in the degradation and biphenyl or 4-chlorobiphenyl identified in Ralstonia eutropha A5, displays a modular structure including a phage-like integrase gene (int), a Pseudomonas-like (chloro)biphenyl catabolic gene cluster (bph), and RP4- and Ti-plasmid-like transfer genes (trb) (C. Merlin, D. Springael, and A. Toussaint, Plasmid 41:40-54, 1999). Southern blot hybridization was used to examine the presence of different regions of Tn4371 in a collection of (chloro)biphenyl-degrading bacteria originating from different habitats and belonging to different bacterial genera. Tn4371-related sequences were never detected on endogenous plasmids. Although the gene probes containing only bph sequences hybridized to genomic DNA from most strains tested, a limited selection of strains, all beta-proteobacteria, displayed hybridization patterns similar to the Tn4371 bph cluster. Homology between Tn4371 and DNA of two of those strains, originating from the same area as strain A5, extended outside the catabolic genes and covered the putative transfer region of Tn4371. On the other hand, none of the (chloro)biphenyl degraders hybridized with the outer left part of Tn4371 containing the int gene. The bph catabolic determinant of the two strains displaying homology to the Tn4371 transfer genes and a third strain isolated from the A5 area could be mobilized to a R. eutropha recipient, after insertion into an endogenous or introduced IncP1 plasmid. The mobilized DNA of those strains included all Tn4371 homologous sequences previously identified in their genome. Our observations show that the bph genes present on Tn4371 are highly conserved between different (chloro)biphenyl-degrading hosts, isolated globally but belonging mainly to the beta-proteobacteria. On the other hand, Tn4371-related mobile elements carrying bph genes are apparently only found in isolates from the environment that provided the Tn4371-bearing isolate A5.

A GntR-like negative regulator of the biphenyl degradation genes of the transposon Tn4371

Tn4371, a 55-kb catabolic transposon originally isolated from Ralstonia eutropha A5, carries genes for the degradation of biphenyl/4-chlorobiphenyl, which are clustered on a 13-kb DNA segment located in the middle of the element. DNA sequencing revealed that two potential regulatory genes, bphR and bphS, border this region. Transcriptional fusion experiments using bphC as a reporter gene, Northern hybridization and primer extension analysis led to the conclusion that the transposon-encoded genes bphEFGA1A2A3BCD form an operon transcribed from a sigma70 promoter, pE. Transcription from pE was not influenced by deletion of the bphR gene of Tn4371, which should encode a LysR-like regulator. The bphS gene product negatively regulated pE, and displayed significant similarity to GntR-like regulators. This is the first reported example of a GntR-like regulator involved in the control of an aromatic degradation pathway.

Starvation-induced Mucts62-mediated coding sequence fusion: a role for ClpXP, Lon, RpoS and Crp

The formation of araB-lacZ coding sequence fusions in Escherichia coli is a particular type of chromosomal rearrangement induced by Mucts62, a thermoinducible mutant of mutator phage Mu. Fusion formation is controlled by the host physiology. It only occurs after aerobic carbon starvation and requires the phage-encoded transposase pA, suggesting that these growth conditions trigger induction of the Mucts62 prophage. Here, we show that thermal induction of the prophage accelerated araB-lacZ fusion formation, confirming that derepression is a rate-limiting step in the fusion process. Nonetheless, starvation conditions remained essential to complete fusions, suggesting additional levels of physiological regulation. Using a transcriptional fusion indicator system in which the Mu early lytic promoter is fused to the reporter E. coli lacZ gene, we confirmed that the Mucts62 prophage was derepressed in stationary phase (S derepression) at low temperature. S derepression did not apply to prophages that expressed the Mu wild-type repressor. It depended upon the host ClpXP and Lon ATP-dependent proteases and the RpoS stationary phase-specific sigma factor, but not upon Crp. None of these four functions was required for thermal induction. Crp was required for fusion formation, but only when the Mucts62 prophage encoded the transposition/replication activating protein pB. Finally, we found that thermally induced cultures did not return to the repressed state when shifted back to low temperature and, hence, remained activated for accelerated fusion formation upon starvation. The maintenance of the derepressed state required the ClpXP and Lon host proteases and the prophage Ner-regulatory protein. These observations illustrate how the cts62 mutation in Mu repressor provides the prophage with a new way to respond to growth phase-specific regulatory signals and endows the host cell with a new potential for adaptation through the controlled use of the phage transposition machinery.

Tn4371: A modular structure encoding a phage-like integrase, a Pseudomonas-like catabolic pathway, and RP4/Ti-like transfer functions

Tn4371 is a 55-kb catabolic transposon originally isolated from Ralstonia eutropha A5 that encodes enzymes catalyzing the complete degradation of biphenyl. Unlike previously described transposons encoding similar genes for aromatic compound degradation. Tn4371 carries a phage-like degradation, Tn4371 integrase gene and RP4/Ti-like transfer genes. Tn4371 transposition involves an excision/integration process and, consistent with this site-specific recombination mechanism, the ends of the element are transiently covalently bound. Transposition is targeted to a limited number of sites on the CH34 chromosome and pMOL30 plasmid as well as on RP4. One of these sites consists of a 5'-TTTTTCAT-3' sequence which is also present between the covalently joined ends of the transposon. Conjugative transfer of Tn4371 could not yet be demonstrated although the functionality of its transfer machinery could be established through the identification of a second transposable element, Tn-bph, which contains the right half of Tn4371, including the bph catabolic gene cluster and the identified transfer genes. Tn-bph transfers by conjugation and integrates in a new host genome independently of the larger element. Tn4371 thus appears as composite transposon combining an enteric phage-like integration system, RP4/Ti-like conjugation genes, and Pseudomonas-like catabolic genes.

Assembly of both the head and tail of bacteriophage Mu is blocked in Escherichia coli groEL and groES mutants

Like several other Escherichia coli bacteriophages, transposable phage Mu does not develop normally in groE hosts (M. Pato, M. Banerjee, L. Desmet, and A. Toussaint, J. Bacteriol. 169:5504-5509, 1987). We show here that lysates obtained upon induction of groE Mu lysogens contain free inactive tails and empty heads. GroEL and GroES are thus essential for the correct assembly of both Mu heads and Mu tails. Evidence is presented that groE mutations inhibit processing of the phage head protein gpH as well as the formation of a 25S complex suspected to be an early Mu head assembly intermediate.

In vivo mutational analysis of bacteriophage Mu operators

In bacteria lysogenic for bacteriophage Mu, the phage repressor binds to a tripartite operator region, O1,O2,O3, to repress the lytic promoter pE, located in O2, and negatively autoregulate its own synthesis at the pCM promoter located in O3. We isolated and characterized operator mutations which lead to derepression of pE. Their location in the first and third repressor-consensus-binding sequences in O2 confirms the importance of these sites for repressor/operator interactions.

Organisation of the bph gene cluster of transposon Tn4371, encoding enzymes for the degradation of biphenyl and 4-chlorobiphenyl compounds

Tn4371 is a 55 kb transposon which encodes enzymes for the degradation of biphenyl and 4-chlorobiphenyl compounds into benzoate and 4-chlorobenzoate derivatives. We constructed a cosmid library of Tn4371 DNA. The bph genes involved in biphenyl/4-chlorobiphenyl degradation were found to be clustered in the middle of the transposon. Sequencing revealed an organisation of the bph genes similar to that previously found in Pseudomonas sp. KKS102, i.e. the bphEGF genes are located upstream of bphA1A2A3 and bphA4 is separated from bphA1A2A3 by bphBCD. Consensus sequences for sigma54-associated RNA polymerase were found upstream of bphA1 and bphEGF. Plasmid RP4::Tn4371 was transferred into a mutant of Alcaligenes eutrophus H16 lacking sigma54. In contrast to wild-type H16 exconjugants, the sigma54 mutant exconjugants could not grow on biphenyl, indicating the dependence of Tn4371 bph gene expression on sigma54. The Tn4371-encoded bph pathway was activated when biphenyl and various biphenyl-like compounds were present in the growth medium. Preliminary observations indicate the presence of a region outside the catabolic genes downstream of bphA4 which is involved in mediating at least the basal expression of BphC.

Characterisation of a chromosomally encoded catechol 1,2-dioxygenase (E.C. 1.13.11.1) from Alcaligenes eutrophus CH34

Alcaligenes eutrophus CH34 used benzoate as a sole source of carbon and energy, degrading it through the 3-oxoadipate pathway. All the enzymes required for this degradation were shown to be encoded by chromosomal genes. Catechol 1,2-dioxygenase activity was induced by benzoate, catechol, 4-chlorocatechol, and muconate. The enzyme is most likely a homodimer, with an apparent molecular weight of 76,000 +/- 500. According to several criteria, its properties are intermediate between those of catechol 1,2-dioxygenases (CatA) and chlorocatechol 1,2-dioxygenases (ClcA). The determined Km for catechol is the lowest among known catechol and chlorocatechol dioxygenases. Similar Km values were found for para-substituted catechols, although the catalytic constants were much lower. The catechol 1,2-dioxygenase from strain CH34 is unique in its property to transform tetrachlorocatechol; however, excess substrate led to a marked reversible inhibition. Some meta- and multi-substituted catechols behaved similarly. The determined Km (or Ki) values for para- or meta-substituted catechols suggest that the presence of an electron-withdrawing substituent at one of these positions results in a higher affinity of the enzyme for the ligand. Results of studies of recognition by the enzyme of various nonmetabolised aromatic compounds are also discussed.

C-terminal deletions can suppress temperature-sensitive mutations and change dominance in the phage Mu repressor

Mutations in an N-terminal 70-amino acid domain of bacteriophage Mu's repressor cause temperature-sensitive DNA-binding activity. Surprisingly, amber mutations can conditionally correct the heat-sensitive defect in three mutant forms of the repressor gene, cts25 (D43-G), cts62 (R47-Q) and cts71 (M28-I), and in the appropriate bacterial host produce a heat-stable Sts phenotype (for survival of temperature shifts). Sts repressor mutants are heat sensitive when in supE or supF hosts and heat resistant when in Sup degrees hosts. Mutants with an Sts phenotype have amber mutations at one of three codons, Q179, Q187, or Q190. The Sts phenotype relates to the repressor size: in Sup degrees hosts sts repressors are shorter by seven, 10, or 18 amino acids compared to repressors in supE or supF hosts. The truncated form of the sts62-1 repressor, which lacks 18 residues (Q179-V196), binds Mu operator DNA more stably at 42 degrees in vitro compared to its full-length counterpart (cts62 repressor). In addition to influencing temperature sensitivity, the C-terminus appears to control the susceptibility to in vivo Clp proteolysis by influencing the multimeric structure of repressor.

Bacteriophage Mu repressor as a target for the Escherichia coli ATP-dependent Clp Protease

Bacteriophage Mu repressor, which is stable in its wildtype form, can mutate to become sensitive to its Escherichia coli host ATP-dependent ClpXP protease. We further investigated the determinants of the mutant repressor's sensitivity to Clp. We show the crucial importance of a C-terminal, seven amino acid long sequence in which a single change is sufficient to decrease the rate of degradation of the protein. The sequence was fused at the C-terminal end of the CcdB and CcdA proteins encoded by plasmid F. CcdB, which is naturally stable, was unaffected, while CcdA, which is normally degraded by the Lon protease, became a substrate for ClpXP while remaining a substrate for Lon. In agreement with the current hypothesis on the mechanism of recognition of their substrates by energy- dependent proteases, these results support the existence, on the substrate polypeptides, of separate motifs responsible for recognition and cleavage by the protease.

The Escherichia coli DnaK chaperone machine and bacteriophage Mu late transcription

Bacteriophage Mu does not grow on temperature-sensitive E. coli dnaK mutants at elevated temperatures because of a defect in late transcription. As the Mu-encoded C protein is required for activation of transcription from the phage late promoters, we attempted to determine if DnaK and its accessory proteins DnaJ and GrpE are required for synthesis of C protein or at a later step. We found that the chaperones act in Mu late transcription beyond C-protein synthesis, and that C-protein stability is decreased in the mutant hosts. This suggests that the DnaK chaperone machine may be required for the proper folding and/or multimerization of C protein.

Introduction of Pseudomonas aeruginosa mutator phage D3112 into Alcaligenes eutrophus strain CH34

We have investigated the possibility of growing mutator phages from Pseudomonas aeruginosa on various isolates of Alcaligenes eutrophus. Although none out of 10 A. eutrophus strains were susceptible to infection with any of the phages tested, phage D3112 could be readily transferred in our model strain CH34 by means of an RP4::D3112 plasmid. CH34/RP4::D3112 lysogens were stable and produced phages. However, neither mitomycin C nor UV treatment increased the phage yield.

A new component of bacteriophage Mu replicative transposition machinery: the Escherichia coli ClpX protein

We have shown previously that some particular mutations in bacteriophage Mu repressor, the frameshift vir mutations, made the protein very sensitive to the Escherichia coli ATP-dependent Clp protease. This enzyme is formed by the association between a protease subunit (ClpP) and an ATPase subunit. ClpA, the best characterized of these ATPases, is not required for the degradation of the mutant Mu repressors. Recently, a new potential ClpP associated ATPase, ClpX, has been described. We show here that this new subunit is required for Mu vir repressor degradation. Moreover, ClpX (but not ClpP) was found to be required for normal Mu replication. Thus ClpX has activities that do not require its association with ClpP. In the pathway of Mu replicative transposition, the block resides beyond the strand transfer reaction, i.e. after the transposition reaction per se is completed, suggesting that ClpX is required for the transition to the formation of the active replication complex at one Mu end. This is a new clear-cut case of the versatile activity of polypeptides that form multi-component ATP-dependent proteases.

Regulation of bacteriophage Mu transposition

Bacteriophage Mu is a transposon and a temperate phage which has become a paradigm for the study of the molecular mechanism of transposition. As a prophage, Mu has also been used to study some aspects of the influence of the host cell growth phase on the regulation of transposition. Through the years several host proteins have been identified which play a key role in the replication of the Mu genome by successive rounds of replicative transposition as well as in the maintenance of the repressed prophage state. In this review we have attempted to summarize all these findings with the purpose of emphasizing the benefit the virus and the host cell can gain from those phage-host interactions.

Identification of the integration host factor genes of Erwinia chrysanthemi 3937

Two Erwinia chrysanthemi homologues of the himA and himD genes of Escherichia coli which encode the integration host factor (IHF) were cloned, sequenced and compared to their homolog in other enterobacteria (EMBL accession nos X74749 and X74750). Both genes were inactivated by the insertion of an antibiotic resistance cassette, allowing for the isolation of IHF- mutants of E chrysanthemi.

Characterization of a temperate phage hosted by Alcaligenes eutrophus strain A5

Nineteen strains of Alcaligenes eutrophus were tested for the presence of prophages. One strain that lysed upon mitomycin C treatment produced a phage which could not form plaques on any of the strains available. DNA extracted from partially purified phage lysates was digested with various restriction enzymes which showed that the 42 kb long viral double-stranded DNA circularizes by means of cohesive ends. To our knowledge, this is the first description of a phage for the genus Alcaligenes.

Virulence in bacteriophage Mu: a case of trans-dominant proteolysis by the Escherichia coli Clp serine protease

The importance of proteases in gene regulation is well documented in both prokaryotic and eukaryotic systems. Here we describe the first example of genetic regulation controlled by the Escherichia coli Clp ATP-dependent serine protease. Virulent mutants of bacteriophage Mu, which carry a particular mutation in their repressor gene (vir mutation), successfully infect Mu lysogens and induce the resident Mu prophage. We show that the mutated repressors have an abnormally short half-life due to an increased susceptibility to Clp-dependent degradation. This susceptibility is communicated to the wild type repressor present in the same cell, which provides the Muvir phages with their trans-dominant phenotype. To our knowledge this is the first case where the instability of a mutant protein is shown to trigger the degradation of its wild type parent.

Cloning and sequencing of IS1086, an Alcaligenes eutrophus insertion element related to IS30 and IS4351

A new insertion sequence (IS), designated IS1086, was isolated from Alcaligenes eutrophus CH34 by being trapped in plasmid pJV240, which contains the Bacillus subtilis sacB and sacR genes. The 1,106-bp IS1086 element contains partially matched (22 of 28 bp) terminal-inverted repeats and a long open reading frame. Hybridization data suggest the presence of one copy of IS1086 in the strain CH34 heavy-metal resistance plasmid pMOL28 and at least two copies in its chromosome. Analysis of the IS1086 nucleotide sequence revealed striking homology with two other IS elements, IS30 and IS4351, suggesting that they are three close members in a family of phylogenetically related insertion sequences. One open reading frame of the Spiroplasma citri phage SpV1-R8A2 B was also found to be related to this IS family but to a lesser extent. Comparison of the G+C contents of IS30 and IS1086 revealed that they conform to their respective hosts (46 versus 50% for IS30 and Escherichia coli and 64.5% for IS1086 and A. eutrophus). The pressure on the AT/GC ratio led to a very different codon usage in these two closely related IS elements. Results suggesting that IS1086 transposition might be activated by some forms of stress are discussed.

Stabilization of bacteriophage Mu repressor-operator complexes by the Escherichia coli integration host factor protein

All of the previously described effects of integration host factor (IHF) on bacteriophage Mu development have supported the view that IHF favours transposition-replication over the alternative state of lysogenic phage growth. In this report we show that, consistent with a model in which Mu repressor binding to its operators requires a particular topology of the operator DNA, IHF stimulates repressor binding to the O1 and O2 operators and enhances Mu repression. IHF would thus be one of the keys, besides supercoiling and the H-NS protein, that lock the operator region into the appropriate topological conformation for high-affinity binding not only of the phage transposase but also of the phage repressor.

Frameshift mutations in the bacteriophage Mu repressor gene can confer a trans-dominant virulent phenotype to the phage

Virulent mutations in the bacteriophage Mu repressor gene were isolated and characterized. Recombination and DNA sequence analysis have revealed that virulence is due to unusual frameshift mutations which change several C-terminal amino acids. The vir mutations are in the same repressor region as the sts amber mutations which, by eliminating several C-terminal amino acids, suppress thermosensitivity of repressor binding to the operators by its N-terminal domain (J. L. Vogel, N. P. Higgins, L. Desmet, V. Geuskens, and A. Toussaint, unpublished data). Vir repressors bind Mu operators very poorly. Thus the Mu repressor C terminus, either by itself or in conjunction with other phage or host proteins, tunes the DNA-binding properties at the repressor N terminus.

Temperature-sensitive mutations in the bacteriophage Mu c repressor locate a 63-amino-acid DNA-binding domain

Phage Mu's c gene product is a cooperative regulatory protein that binds to a large, complex, tripartite 184-bp operator. To probe the mechanism of repressor action, we isolated and characterized 13 phage mutants that cause Mu to undergo lytic development when cells are shifted from 30 to 42 degrees C. This collection contained only four mutations in the repressor gene, and all were clustered near the N terminus. The cts62 substitution of R47----Q caused weakened specific DNA recognition and altered cooperativity in vitro. A functional repressor with only 63 amino acids of Mu repressor fused to a C-terminal fragment of beta-galactosidase was constructed. This chimeric protein was an efficient repressor, as it bound specifically to Mu operator DNA in vitro and its expression conferred Mu immunity in vivo. A DNA looping model is proposed to explain regulation of the tripartite operator site and the highly cooperative nature of repressor binding.