Characterization of ToxINPa-sensitive bacteriophages of Serratia sp. ATCC 39006

Abortive infection (Abi) is an anti-phage mechanism in which a bacterium initiates its own death upon phage infection. This prevents or decreases the production of phage progeny and protects clonal siblings in the bacterial population by an act akin to an “altruistic suicide.” Abortive infection can be mediated by a Type III toxin-antitoxin system called ToxINPa, first found in Pectobacterium atrosepticum. ToxINPa consists of an endoribonuclease toxin and RNA antitoxin and is inactive as a heterohexameric complex until infection by certain phages causes destabilization of ToxINPa, leading to bacteriostasis and, eventually, lethality. However, it is still unknown why only certain phages are able to activate ToxINPa-mediated Abi and what mechanisms are involved. This study aimed to address this issue by first introducing ToxINPa into the Gram-negative enterobacterium, Serratia sp. ATCC 39006 (S39006). A novel environmental S39006 phage, ΦCBH8, that is sensitive to ToxINPa-mediated Abi was isolated, characterized, and compared to its spontaneous “escape” mutants that were insensitive to ToxINPa. Characterization of ΦCBH8 led to the discovery of a new genus of T4-family phages that are all ToxINPa-sensitive. Genomic comparison of ΦCBH8 with its spontaneous ToxINPa-escape mutants led to the discovery of two distinct genetic loci that are candidates for activation of ToxINPa-mediated Abi. One such locus was a multi-gene region of the phage genome, the deletion of which enabled some ΦCBH8 mutants to escape ToxINPa. Different ToxINPa-escape mutants had variable deletions in their genomes, but this multi-gene locus was deleted in all of the deletion mutants. Experiments showed that at least two genes in this locus must be simultaneously involved in activating ToxINPa-mediated Abi and one phage gene product within the locus (ORF18) was extremely toxic to the bacterial host. Another locus was the asiA gene. This study showed that ΦCBH8 mutants with mutated versions of asiA became insensitive to ToxINPa but genetic complementation restored their sensitivity. AsiA is involved in σ-appropriation but the mutated AsiA in ΦCBH8 mutants was no longer functional. Further experiments showed that AsiA from wild type ΦCBH8 reduced ToxINPa promoter activity while mutant AsiA did not, suggesting that AsiA could be involved in activating ToxINPa-mediated Abi by perturbing toxINPa transcription. Finally, an outer membrane protein (OmpW) was defined as the ΦCBH8 receptor in S39006. Transfer of the S39006 ompW gene to other bacterial species rendered some of them sensitive to the phage thereby enabling expansion of ΦCBH8 host range. Results showed that ΦCBH8 was insensitive to ToxINPa in E.coli, suggesting that activation of ToxINPa-mediated Abi is host-dependent. The function of OmpW was explored to try to link bacterial host physiology with phage susceptibility In conclusion, this work characterized novel phage genes involved in activating ToxINPa-mediated Abi. This provided evidence that viral gene lethality and σ-appropriation might be related to the mechanism(s) for phage activation of ToxINPa-mediated Abi.

The prophages of Citrobacter rodentium represent a conserved family of horizontally-acquired mobile genetic elements associated with enteric evolution towards pathogenicity

Prophage mediated horizontal gene transfer (HGT) plays a key role in the evolution of bacteria, enabling access to new environmental niches, including pathogenicity. Citrobacter rodentium is a host-adapted intestinal mouse pathogen and important model organism for attaching and effacing (A/E) pathogens including the clinically significant enterohaemorrhagic (EHEC) and enteropathogenic (EPEC) Escherichia coli. Despite containing ten prophage genomic regions, including an active temperate phage, ΦNP, little was known regarding the nature of C. rodentium prophages in the bacterium’s evolution towards pathogenicity. In this study, our characterization of ΦNP led to the discovery of a second, fully functional temperate phage, named ΦSM. We identify the bacterial host-receptor for both phages as lipopolysaccharide (LPS). ΦNP and ΦSM are likely important mediators of HGT in C. rodentium. Bioinformatic analysis of the ten prophage regions reveals cargo genes encoding known virulence factors, including several Type III secretion system (T3SS) effectors. C. rodentium prophages are conserved across a wide range of pathogenic enteric bacteria, including EPEC and EHEC as well as pathogenic strains of Salmonella enterica, Shigella boydii, and Klebsiella pneumoniae. Phylogenetic analysis of core enteric backbone genes compared against prophage evolutionary models suggests that these prophages represent an important, conserved family of horizontally acquired enteric-associated pathogenicity determinants. In addition to highlighting the transformative role of bacteriophage mediated HGT in C. rodentium’s evolution towards pathogenicity, these data suggest that the examination of conserved families of prophages in other pathogenic bacteria and disease outbreaks might provide deeper evolutionary and pathological insights otherwise obscured by more classical analysis.BBSRC and China Scholarship Council and the Cambridge Commonwealth, European, and International Trust

Structure, Evolution, and Functions of Bacterial Type III Toxin-Antitoxin Systems.

Toxin-antitoxin (TA) systems are small genetic modules that encode a toxin (that targets an essential cellular process) and an antitoxin that neutralises or suppresses the deleterious effect of the toxin. Based on the molecular nature of the toxin and antitoxin components, TA systems are categorised into different types. Type III TA systems, the focus of this review, are composed of a toxic endoribonuclease neutralised by a non-coding RNA antitoxin in a pseudoknotted configuration. Bioinformatic analysis shows that the Type III systems can be classified into subtypes. These TA systems were originally discovered through a phage resistance phenotype arising due to a process akin to an altruistic suicide; the phenomenon of abortive infection. Some Type III TA systems are bifunctional and can stabilise plasmids during vegetative growth and sporulation. Features particular to Type III systems are explored here, emphasising some of the characteristics of the RNA antitoxin and how these may affect the co-evolutionary relationship between toxins and cognate antitoxins in their quaternary structures. Finally, an updated analysis of the distribution and diversity of these systems are presented and discussed.Work in the Salmond lab is supported by the BBSRC, UK; N.G. was supported by the Fonds National de la Recherche Luxembourg (9118191); B.C. was supported by a Cambridge International Scholarship from the Cambridge Commonwealth, European & International Trust; and A.D. was supported by a BBSRC -DTP studentship.This is the final version of the article. It first appeared from Molecular Diversity Preservation International via https://doi.org/10.3390/toxins810028

Impact of Bivalirudin on Ischemia/Reperfusion Injury in Patients with Reperfused STEMI Assessed by Cardiac Magnetic Resonance

Thrombin is an important ischemia/reperfusion injury (IRI) mediator in patients with ST-elevation myocardial infarction (STEMI). This study examines the use of bivalirudin, a direct thrombin inhibitor, in reducing IRI in STEMI patients. STEMI patients (n = 21) were treated with bivalirudin and compared to 21 patients treated with unfractionated heparin (UFH) from the EARLY Assessment of Myocardial Tissue Characteristics by CMR in STEMI (EARLY-MYO-CMR) registry (NCT03768453). Infarct size (IS) and left ventricular ejection fraction (LVEF) were comparable between the two groups at follow up. During the first cardiac magnetic resonance (CMR) scan within the first week after percutaneous coronary intervention (PCI), all patients in both the bivalirudin and UFH groups exhibited myocardial edema. However, the myocardium edema volume was significantly less in the bivalirudin group (p p p < 0.05). These findings were corroborated by T2 and T1 mapping results. The study concluded that the use of bivalirudin for anticoagulation is associated with attenuated IRI in STEMI patients who receive primary PCI

Flame-retardant polyvinyl alcohol/cellulose nanofibers hybrid carbon aerogel by freeze drying with ultra-low phosphorus

Polyvinyl alcohol/cellulose nanofibers hybrid aerogel was prepared under freeze drying method. To improve the aerogels' anti-combustion performance, 0.8 wt% microencapsulated ammonium polyphosphate (MCAPP) was loaded as the flame retardant. Aerogels with extremely low density (~0.06 g/cm3) and excellent mechanical performance (Young's modulus: 1.045 MPa) can be obtained. The resulted aerogel also exhibit considerable thermal insulation ability (thermal conductivity: ~0.04 W/m·K). Experimental results indicate that the value of limiting oxygen index increases from 19.5% to 37.5% when loading 0.8 wt% MCAPP. Accordingly, the aerogels' peak heat release rate decreased significantly from 222.44 to 107.84 kW/m2. The char residue rises when introducing MCAPP and the char's integrity improves a lot after combustion. The fire performance index and fire growth index increases and falls respectively, indicating improved anti-combustion performance. X-ray photoelectron spectroscopy results show C[dbnd]O bonds would be increased for the esterification of phosphoric acid from MCAPP. In addition, the production of carbonate can be prohibited while combustion when loading MCAPP

Numerical Simulation on the Effect of Fire Shutter Descending Height on Smoke Extraction Efficiency in a Large Atrium

In this study, a series of numerical simulations were carried out to investigate the effect of fire shutter descending height on the smoke extraction efficiency in a large space atrium. Based on the full-scale fire experiments, this paper carried out more numerical simulations to explore factors affecting the smoke extraction efficiency in the atrium. The smoke flow characteristics, temperature distribution law and smoke extraction efficiency of natural and mechanical smoke exhaust systems were discussed under different heat release rates and fire shutter descending heights. The results show that the smoke spread rate and the average temperature of the smoke are higher with a greater heat release rate. After the mechanical smoke exhaust system is activated, the smoke layer thickness and smoke temperature decrease, and the stable period of heat release rate is shorter. In the condition of natural smoke exhaust, the smoke extraction efficiency increases exponentially with the increase of heat release rate and the descending height of the fire shutter, and the maximum smoke extraction efficiency is 48.8%. In the condition of mechanical smoke exhaust, the smoke extraction efficiency increases with the increase of mechanical exhaust velocity. When the velocity increases to the critical value (8 m/s), the smoke extraction efficiency is essentially stable. The smoke extraction efficiency is increased first with the increase of fire shutter descending height and then has a downward trend when the descending height drops to half, and the maximum smoke extraction efficiency is 70.3% in the condition of mechanical smoke exhaust. Empirical correlations between the smoke extraction efficiency and the dimensionless fire shutter descending height, the dimensionless heat release rate and the dimensionless smoke exhaust velocity have been established. The results of this study can provide a reference for the design of smoke prevention and exhaust systems in the atrium

Numerical Simulation on the Effect of Fire Shutter Descending Height on Smoke Extraction Efficiency in a Large Atrium

In this study, a series of numerical simulations were carried out to investigate the effect of fire shutter descending height on the smoke extraction efficiency in a large space atrium. Based on the full-scale fire experiments, this paper carried out more numerical simulations to explore factors affecting the smoke extraction efficiency in the atrium. The smoke flow characteristics, temperature distribution law and smoke extraction efficiency of natural and mechanical smoke exhaust systems were discussed under different heat release rates and fire shutter descending heights. The results show that the smoke spread rate and the average temperature of the smoke are higher with a greater heat release rate. After the mechanical smoke exhaust system is activated, the smoke layer thickness and smoke temperature decrease, and the stable period of heat release rate is shorter. In the condition of natural smoke exhaust, the smoke extraction efficiency increases exponentially with the increase of heat release rate and the descending height of the fire shutter, and the maximum smoke extraction efficiency is 48.8%. In the condition of mechanical smoke exhaust, the smoke extraction efficiency increases with the increase of mechanical exhaust velocity. When the velocity increases to the critical value (8 m/s), the smoke extraction efficiency is essentially stable. The smoke extraction efficiency is increased first with the increase of fire shutter descending height and then has a downward trend when the descending height drops to half, and the maximum smoke extraction efficiency is 70.3% in the condition of mechanical smoke exhaust. Empirical correlations between the smoke extraction efficiency and the dimensionless fire shutter descending height, the dimensionless heat release rate and the dimensionless smoke exhaust velocity have been established. The results of this study can provide a reference for the design of smoke prevention and exhaust systems in the atrium