VgrG Spike Dictates PAAR Requirement for the Assembly of the Type VI Secretion System.

Widely employed by Gram-negative pathogens for competition and pathogenesis, the type six protein secretion system (T6SS) can inject toxic effectors into neighboring cells through the penetration of a spear-like structure comprising a long Hcp tube and a VgrG-PAAR spike complex. The cone-shaped PAAR is believed to sharpen the T6SS spear for penetration but it remains unclear why PAAR is required for T6SS functions in some bacteria but dispensable in others. Here, we report the conditional requirement of PAAR for T6SS functions in Aeromonas dhakensis, an emerging human pathogen that may cause severe bacteremia. By deleting the two PAAR paralogs, we show that PAAR is not required for T6SS secretion, bacterial killing, or specific effector delivery in A. dhakensis. By constructing combinatorial PAAR and vgrG deletions, we demonstrate that deletion of individual PAAR moderately reduced T6SS functions but double or triple deletions of PAAR in the vgrG deletion mutants severely impaired T6SS functions. Notably, the auxiliary-cluster-encoded PAAR2 and VgrG3 are less critical than the main-cluster-encoded PAAR1 and VgrG1&2 proteins to T6SS functions. In addition, PAAR1 but not PAAR2 contributes to antieukaryotic virulence in amoeba. Our data suggest that, for a multi-PAAR T6SS, the variable role of PAAR paralogs correlates with the VgrG-spike composition that collectively dictates T6SS assembly. IMPORTANCE Gram-negative bacteria often encode multiple paralogs of the cone-shaped PAAR that sits atop the VgrG-spike and is thought to sharpen the spear-like T6SS puncturing device. However, it is unclear why PAAR is required for the assembly of some but not all T6SSs and why there are multiple PAARs if they are not required. Our data delineate a VgrG-mediated conditional requirement for PAAR and suggest a core-auxiliary relationship among different PAAR-VgrG modules that may have been acquired sequentially by the T6SS during evolution.

The image quality, lesion detectability, and acquisition time of 18F-FDG total-body PET/CT in oncological patients.

PURPOSE: The purpose was to investigate the effects of short acquisition time on the image quality and the lesion detectability of oncological 18F-FDG total-body PET/CT. METHODS: Nineteen oncological patients (6/13 women/men, age 65.6 ± 9.4 years) underwent total-body PET/CT on uEXPLORER scanner using 3D list mode. The administration of 18F-FDG was weight-based (4.4 MBq/kg). The acquisition time was 900 s, and PET data were reconstructed into 900-, 180-, 120-, 60-, 30-, and 18-s duration groups. The subjective PET image quality was scored using a 5-point scale (5, excellent; 1, poor) in 3 perspectives: overall quality, noise, and lesion conspicuity. The objective image quality was evaluated by SUVmax and standard deviation (SD) of the liver, SUVmax of the tumor, and tumor-to-background ratio (TBR). The lesion detectability was the percentage of identifiable lesions in the groups of 180 to 18 s using the group 900 s as reference. RESULTS: Our results showed that sufficient and acceptable subjective image quality could be achieved with 60- and 30-s groups, and good image quality scores were given to 180- and 120-s groups without significant difference. For shortened acquisition time, SD was increased, while SUVmax of tumor and TBR remained unchanged. The lesion detectability was decreased with shorter acquisition time, but the detection performance could be maintained until the 60-s group compared with the 900-s group, although the image quality degraded. CONCLUSION: The total-body PET/CT can significantly shorten the acquisition time with maintained lesion detectability and image quality.

Filamentous prophage Pf4 promotes genetic exchange in Pseudomonas aeruginosa.

Filamentous prophages are widespread among bacteria and play crucial functions in virulence, antibiotic resistance, and biofilm structures. The filamentous Pf4 particles, extruded by an important pathogen Pseudomonas aeruginosa, can protect producing cells from adverse conditions. Contrary to the conventional belief that the Pf4-encoding cells resist reinfection, we herein report that the Pf4 prophage is reciprocally and commonly exchanged within P. aeruginosa colonies, which can repair defective Pf4 within the community. By labeling the Pf4 locus with antibiotic resistance and fluorescence markers, we demonstrate that the Pf4 locus is frequently exchanged within colony biofilms, in artificial sputum media, and in infected mouse lungs. We further show that Pf4 trafficking is a rapid process and capable of rescuing Pf4-defective mutants. The Pf4 phage is highly adaptable and can package additional DNA doubling its genome size. We also report that two clinical P. aeruginosa isolates are susceptible to the Pf4-mediated exchange, and the Pf5 prophage can be exchanged between cells as well. These findings suggest that the genetic exchanging interactions by filamentous prophages may facilitate defect rescue and the sharing of prophage-dependent benefits and costs within the P. aeruginosa community.

[Hepatocellular carcinoma and angiogenesis imaging using synchrotron radiation].

OBJECTIVE: To investigate the potential utility of microangiography with synchrotron radiation to detect murine hepatocellular carcinoma (HCC) angiogenesis using an ex vivo model system. METHODS: An HCC xenograft model was established by implanting HCCLM3 cells into male mice livers (n = 6). Twenty-eight days later, three of the mice were randomly selected for barium sulfate infusion into the liver and tumor via the inferior vena cava followed by ligation of the arteries, veins and common bile duct; the remaining three mice were left untreated and served as controls. All mice were sacrificed to collect livers for analysis using the BL13W beamline X-ray imager (Shanghai Synchrotron Radiation Facility, China). In addition, the tumor vasculature was evaluated by immunostaining of formalin-fixed tissues for CD31, CD34, and F8. RESULTS: High resolution images of tumor angiogenesis were acquired and image analysis indicated that the normal blood vessels had been displaced by the fast growing tumors. Abundant and tortuous tumor angiogenesis in the tumor periphery area and sparse angiogenesis inside the tumor were also visualized clearly. These features were similar to the immunohistological results. The smallest tumor vessels visualized were approximately 20 mum in diameter. CONCLUSION: Microangiography with synchrotron radiation using barium sulfate as contrast agent is a viable imaging strategy for tumor angiogenesis.

[Treatment of serious burst thoracolumbar fracture with posterior pedicle screw fixation, transpedicular bone grafting and vertebral canaloplasty].

OBJECTIVE: To study the clinical results of posterior pedicle screw fixation, transpedicular bone grafting and vertebral canaloplasty with ilium autografting in treating serious burst thoracolumbar fracture. METHODS: From March 2004 to March 2008,10 patients with serious burst thoracolumbar fracture, including 7 males and 3 females with age for 24-58 years (mean 41 years)were treated by posterior pedicle screw fixation, transpedicular bone grafting and total laminectomy with preservation of spinal process and vertebral canaloplasty with ilium autografting. The operative effects were assessed according to Frankel classification and radiologic results. RESULTS: All patients were followed up from 1 to 4 years. There was no loosening or broken in instrumentation. The anterior edge height of the fractured vertebrae body was restored from (21.00 +/- 12.00)% to (95.00 +/- 4.20)%, and the posterior edge height of the fractured vertebrae body was restored from (70.00 +/- 15.00)% to (96.00 +/- 3.20)% postoperatively, which both demonstrated improvement compared with preoperative instance (P < 0.01). The Cobb angle was restored from (32.80 +/- 8.20) degrees to (4.20 +/- 1.60) degrees which also demonstrated improvement compared with the preoperative Cobb angle (P < 0.01). At least one grade recovery was observed in all cases except one patient with preoperative Frankel A degree. The result of Denis classification, P1, had 4 cases, P2 had 4, P3 had 1, P4 had 1. CONCLUSION: Posterior pedicle screw fixation, transpedicular bone grafting and vertebral canaloplasty can obtain satisfactory results treating serious burst thoracolumbar fractures. It is a feasible method with advantages of simple operation, good efficacy, preservation of structure of posterior column which should be applied clinically.