Clinical characteristics and risk factors of diabetic foot ulcers with PAD.

OBJECTIVE: This study aimed to analyze the clinical characteristics of patients with diabetic foot ulcers combined with peripheral arterial disease (PAD) and the risk factors. PATIENTS AND METHODS: A retrospective study was conducted on 120 patients with diabetic foot ulcers in the Second Affiliated Hospital of Dalian Medical University from October 2018 to February 2021. The patients were divided into uncombined with the PAD group (42 cases) and combined with the PAD group (78 cases). The baseline information and clinical indicators were measured from two groups. Univariate and binary logistic regression was used to analyze the risk factors of PAD in patients with diabetic foot ulcers. RESULTS: The proportion of patients with age ≥ 60 years, Wagner grade 4-5 and smoking history in the combined group was higher than that in the uncombined group (p < 0.05). The diastolic blood pressure (DBP) of the combined group was lower than that of the uncombined group, while the C-reactive protein (CRP), neutrophil-to-lymphocyte ratio (NLR) and glycated hemoglobin (HbA1c) levels of the combined group were higher than those of the uncombined group (p < 0.05). Binary logistic regression analysis showed that age ≥ 60 years, high Wagner grade, smoking, elevated CRP, NLR and HbA1c levels were risk factors for patients with diabetic foot ulcer combined with PAD (OR > 1, p < 0.05). An elevated DBP level was the protective factor for PAD in patients with diabetic foot ulcer (OR < 1, p < 0.05). CONCLUSIONS: Patients with diabetic foot ulcer combined with PAD have the clinical characteristics of poor blood pressure control, long course of disease, and low ABI value. Age ≥ 60 years, high Wagner grade, smoking history, elevated CRP, NLR and HbA1c levels are the risk factors of PAD in patients with diabetic foot ulcer. Increased DBP is protective for PAD in patients with diabetic foot ulcer.

Predicting high quality of participation in adaptive snow-sports for individuals with disabilities: An exploratory study.

OBJECTIVES: This exploratory study aimed to examine the individual, program and environmental (social and physical) characteristics which predict high quality of participation in adaptive snowsports for each dimension of the Quality of Participation in Parasport Framework (QPPF): autonomy, belongingness, mastery, challenge, engagement and meaning. METHODS: A survey was completed by 133 individuals with disabilities or their representatives on each dimension of the QPPF in adaptive snowsports and on the factors impacting the quality of participation. Descriptive statistics were used to describe the study participants, and a multivariate logistic regression model was constructed for each dimension of the QPPF to evaluate the relative contribution of individual, snowsport-related, program and environmental factors to each dimension. RESULTS: Individuals with disabilities in this study reported high quality of participation on all dimensions of the QPPF. The individual characteristics only predicted the QPPF dimension of challenge. However, the program and environmental characteristics such as equipment, number of instructors and barriers were robust predictors of quality of participation. CONCLUSION: Overall, participants experienced high quality participation. Supporting the adaptive snowsports programs while reducing the barriers faced by people with disabilities should be a continued effort to promote quality of participation.

[Preliminary exploration of modified side overlap with fundoplication by Yamashita (mSOFY) anastomosis technique in laparoscopic proximal gastrectomy].

Objective: To discuss the feasibility and safety of modified side overlap with fundoplication by Yamashita (mSOFY) in laparoscopic proximal gastrectomy. Methods: Using the method of descriptive case series study, the clinical data of 9 patients with upper gastric cancer who successfully performed mSOFY anastomosis from March 2022 to October 2022 in the Affiliated Huaian No.1 People's Hospital of Nanjing Medical University were retrospectively analyzed.The reconstruction steps of mSOFY anastomosis are as follows: (1) Make a small incision on the right side of the esophageal stump and in front of the anterior wall of the gastric stump; (2) The 45mm linear cutting stapler is placed into the preset anastomosis of the esophagus and the remnant stomach, and the esophagus is rotated 90° counterclockwise along the axis, so that the right wall of the esophagus is anastomosed with the remnant stomach, and the stomach wall is sutured to the left side of the esophagus; (3) The common opening of esophagus and remnant stomach was sutured with inverted suture; (4)Suture the left and lower sides of the esophagus with the remnant stomach to make the esophagus flat against the stomach wall; (5) Open the sutured common opening: due to the pressure of the false dome, the posterior wall of the lower esophageal segment was compressed into a valve-like structure. We mainly observing the postoperative reflux and nutritional improvement of the patients, and recording the intraoperative situation and postoperative complications. Results: Nine patients with upper gastric cancer who completed laparoscopic proximal gastrectomy (mSOFY anastomosis) did not have conversion to laparotomy or intraoperative / postoperative complications. The operation time was (169.4±10.4) minutes, the anastomotic reconstruction time was (51.7±7.1) minutes, the intraoperative bleeding volume was (98.9±43.4) ml, and the number of lymph nodes dissected was (27.2±6.7). The patient recovered well after operation, without any complaints related to reflux esophagitis. Postoperative gastrointestinal radiography showed that the anastomosis was smooth, without stenosis and leakage. The serum albumin [(41.6±3.4) L vs. (39.9±2.6) L], prealbumin [(211.3±38.6) mg/L vs. (205.3±36.0) mg/L], and hemoglobin levels [(126.7±13.2) g/L vs. (121.0±9.7) g/L] of patients before and one month after surgery have no statistically significant differences (all P>0.05). Conclusion: mSOFY anastomosis can be used as one of the safe and feasible reconstruction methods in laparoscopic proximal gastrectomy.

[Network meta-analysis comparing the clinical outcomes and safety of robotic, laparoscopic, and transanal total rectal mesenteric resection for rectal cancer].

Objective: To methodically assess the clinical effectiveness and safety of robot-assisted total rectal mesenteric resection (RTME), laparoscopic-assisted total rectal mesenteric resection (laTME), and transanal total rectal mesenteric resection (taTME). Methods: A computer search was conducted on PubMed, Embase, Cochrane Library, and Ovid databases to identify English-language reports published between January 2017 and January 2022 that compared the clinical efficacy of the three surgical procedures of RTME, laTME, and taTME. The quality of the studies was evaluated using the NOS and JADAD scales for retrospective cohort studies and randomized controlled trials, respectively. Direct meta-analysis and reticulated meta-analysis were performed using Review Manager software and R software, respectively. Results: Twenty-nine publications comprising 8,339 patients with rectal cancer were ultimately included. The direct meta-analysis indicated that the length of hospital stay was longer after RTME than after taTME, whereas according to the reticulated meta-analysis the length of hospital stay was shorter after taTME than after laTME (MD=-0.86, 95%CI: -1.70 to -0.096, P=0.036). Moreover, the incidence of anastomotic leak was lower after taTME than after RTME (OR=0.60, 95%CI: 0.39 to 0.91, P=0.018). The incidence of intestinal obstruction was also lower after taTME than after RTME (OR=0.55, 95%CI: 0.31 to 0.94, P=0.037). All of these differences were statistically significant (all P<0.05). There were no statistically significant differences between the three surgical procedures regarding the number of lymph nodes cleared, length of the inferior rectal margin, or rate of positive circumferential margins (all P>0.05). An inconsistency test using nodal analysis revealed no statistically significant differences between the results of direct and indirect comparisons of the six outcome indicators (all P>0.05). Furthermore, we detected no significant overall inconsistency between direct and indirect evidence. Conclusion: taTME has advantages over RTME and laTME, in terms of radical and surgical short-term outcomes in patients with rectal cancer.

Essential functions of chaperones and adaptors of protein secretion systems in Gram-negative bacteria.

Equipped with a plethora of secreted toxic effectors, protein secretion systems are essential for bacteria to interact with and manipulate their neighboring environment to survive in host microbiota and other highly competitive communities. While effectors have received spotlight attention in secretion system studies, many require accessory chaperone and adaptor proteins for proper folding/unfolding and stability throughout the secretion process. Here, we review the functions of chaperones and adaptors of three protein secretions systems, type 3 secretion system (T3SS), type 4 secretion system (T4SS), and type 6 secretion system (T6SS), which are employed by many Gram-negative bacterial pathogens to deliver toxins to bacterial, plant, and mammalian host cells through direct contact. Since chaperone and adaptor functions of the T3SS and the T4SS are relatively well studied, we discuss in detail the methods of chaperone-facilitated effector secretion by the T6SS and highlight commonalities between the effector chaperone/adaptor proteins of these diverse secretion systems. While the chaperones and adaptors are generally referred to as accessory proteins as they are not directly involved in toxicities to target cells, they are nonetheless vital for the biological functions of the secretion systems. Future research on biochemical and structural properties of these chaperones will not only elucidate the mechanisms of chaperone-effector binding and release process but also facilitate custom design of cargo effectors to be translocated by these widespread secretion systems for biotechnological applications.

Identification of Small Molecule Inhibitors of the Pathogen Box against Vibrio cholerae.

Antimicrobial resistance (AMR) has become a serious public and economic threat. The rate of bacteria acquiring AMR surpasses the rate of new antibiotics discovery, projecting more deadly AMR infections in the future. The Pathogen Box is an open-source library of drug-like compounds that can be screened for antibiotic activity. We have screened molecules of the Pathogen Box against Vibrio cholerae, the cholera-causing pathogen, and successfully identified two compounds, MMV687807 and MMV675968, that inhibit growth. RNA-seq analyses of V. cholerae after incubation with each compound revealed that both compounds affect cellular functions on multiple levels including carbon metabolism, iron homeostasis, and biofilm formation. In addition, whole-genome sequencing analysis of spontaneous resistance mutants identified an efflux system that confers resistance to MMV687807. We also identified that the dihydrofolate reductase is the likely target of MMV675968 suggesting it acts as an analog of trimethoprim but with a MIC 14-fold lower than trimethoprim in molar concentration. In summary, these two compounds that effectively inhibit V. cholerae and other bacteria may lead to the development of new antibiotics for better treatment of the cholera disease. IMPORTANCE Cholera is a serious infectious disease in tropical regions causing millions of infections annually. Vibrio cholerae, the causative agent of cholera, has gained multi-antibiotic resistance over the years, posing greater threat to public health and current treatment strategies. Here we report two compounds that effectively target the growth of V. cholerae and have the potential to control cholera infection.

[Application value of flexible endoscopy and rigid endoscopy in the clinical examination of chronic sinus tract wounds with different shapes].

Objective: To explore the application value of flexible endoscopy and rigid endoscopy in the clinical examination of chronic sinus tract wounds with different shapes. Methods: A retrospective observational study was conducted. From January 1 to December 23, 2019, a total of 46 patients with chronic sinus tract wounds, who met the inclusion criteria were admitted to the Wound Healing Center of Ruijin Hospital Affiliated to Shanghai Jiao Tong University School of Medicine, including 23 males and 23 females, aged 18-81 (48±21) years. On admission, computer tomography (CT) imaging and three-dimensional reconstruction were performed to examine the shapes of wound sinus tract and classify the wounds, with the lengths of wound sinus tract by CT imaging examination (hereinafter referred to as reference lengths) recorded. The lengths of wound sinus tract were examined and measured by rigid endoscopy and flexible endoscopy. The wounds with and without obviously curved sinus tract were classified into curve group and linear group respectively, and the deviation rates between the lengths of wound sinus tract measured by flexible endoscopy or rigid endoscopy and the reference lengths (hereinafter referred to as deviation rates of lengths) in each group were calculated. The difference between the deviation rates of lengths examined by flexible endoscopy and rigid endoscopy and the differences between the above two and the deviation rate of reference lengths (0) in each group were compared. Data were statistically analyzed with paired sample t test and Wilcoxon signed rank sum test. Results: CT imaging and three-dimensional reconstruction showed that there were 4 types of wound sinus tract, including tubular (36/46), lamellar (4/46), club-mallet (4/46), and irregular (2/46) shape. Tubular wounds were further divided into type I (23/36), type L (4/36), and type Y (9/36). Wounds with type I tubular, lamellar, and club-mallet sinus tract were classified into linear group (31/46), while those with type Y tubular, type L tubular, and irregular sinus tract were classified into curve group (15/46). In linear group, the deviation rates of lengths examined and measured by rigid endoscopy and flexible endoscopy were 0. In curve group, the deviation rate of lengths examined and measured by flexible endoscopy was 0 (0, 0.58%), which was significantly lower than 41.18% (31.68%, 48.41%) examined and measured by rigid endoscopy, Z=-3.408, P<0.01; the deviation rate of lengths examined and measured by rigid endoscopy (40±19)% was significantly higher than the deviation rate of reference lengths (t=8.343, P<0.01), while the deviation rate of the lengths examined and measured by flexible endoscopy was similar to the deviation rate of reference lengths (Z=-1.342, P>0.05). Conclusions: Compared with rigid endoscopy, flexible endoscopy can observe the internal characteristics of chronic sinus tract wounds in a wider range in the clinical examination of this kind of wound, especially for the exploration of curved chronic sinus tract wounds. The promotion of this method will be conducive to the diagnosis and treatment of chronic sinus tract wounds.

Engineered Type Six Secretion Systems Deliver Active Exogenous Effectors and Cre Recombinase.

Genetic editing has revolutionized biotechnology, but delivery of endonuclease genes as DNA can lead to aberrant integration or overexpression, leading to off-target effects. Here, we develop a mechanism to deliver Cre recombinase as a protein by engineering the bacterial type six secretion system (T6SS). Using multiple T6SS fusion proteins, Aeromonas dhakensis or attenuated Vibrio cholerae donor strains, and a gain-of-function cassette for detecting Cre recombination, we demonstrate successful delivery of active Cre directly into recipient cells. The most efficient transfer was achieved using a truncated version of PAAR2 from V. cholerae, resulting in a relatively small (118-amino-acid) delivery tag. We further demonstrate the versatility of this system by delivering an exogenous effector, TseC, enabling V. cholerae to kill Pseudomonas aeruginosa. This implies that P. aeruginosa is naturally resistant to all native effectors of V. cholerae and that the TseC chaperone protein is not required for its activity. Moreover, it demonstrates that the engineered system can improve T6SS efficacy against specific pathogens, proposing future application in microbiome manipulation or as a next-generation antimicrobial. Inexpensive and easy to produce, this protein delivery system has many potential applications, ranging from studying T6SS effectors to genetic editing. IMPORTANCE Delivery of protein-based drugs, antigens, and gene-editing agents has broad applications. The type VI protein secretion system (T6SS) can target both bacteria and eukaryotic cells and deliver proteins of diverse size and function. Here, we harness the T6SS to successfully deliver Cre recombinase to genetically edit bacteria without requiring the introduction of exogenous DNA into the recipient cells. This demonstrates a promising advantage over current genetic editing tools that require transformation or conjugation of DNA. The engineered secretion tag can also deliver a heterologous antimicrobial toxin that kills an otherwise unsusceptible pathogen, Pseudomonas aeruginosa. These results demonstrate the potential of T6SS-mediated delivery in areas including genome editing, killing drug-resistant pathogens, and studying toxin functions.

Sensing of intracellular Hcp levels controls T6SS expression in Vibrio cholerae.

The type 6 secretion system (T6SS) is a bacterial weapon broadly distributed in gram-negative bacteria and used to kill competitors and predators. Featuring a long and double-tubular structure, this molecular machine is energetically costly to produce and thus is likely subject to diverse regulation strategies that are largely ill defined. In this study, we report a quantity-sensing control of the T6SS that down-regulates the expression of secreted components when they accumulate in the cytosol due to T6SS inactivation. Using Vibrio cholerae strains that constitutively express an active T6SS, we demonstrate that mRNA levels of secreted components, including the inner-tube protein component Hcp, were down-regulated in T6SS structural gene mutants while expression of the main structural genes remained unchanged. Deletion of both hcp gene copies restored expression from their promoters, while Hcp overexpression negatively impacted expression. We show that Hcp directly interacts with the RpoN-dependent T6SS regulator VasH, and deleting the N-terminal regulator domain of VasH abolishes this interaction as well as the expression difference of hcp operons between T6SS-active and inactive strains. We find that negative regulation of hcp also occurs in other V. cholerae strains and the pathogens Aeromonas dhakensis and Pseudomonas aeruginosa This Hcp-dependent sensing control is likely an important energy-conserving mechanism that enables T6SS-encoding organisms to quickly adjust T6SS expression and prevent wasteful build-up of its major secreted components in the absence of their efficient export out of the bacterial cell.

[Predicting response to non-small cell lung cancer immunotherapy using pre-treatment contrast-enhanced CT texture-based classification].

Objective: To explore the value of pre-treatment contrast-enhanced computed tomography (CT)-based texture analysis in predicting response to non-small cell lung cancer (NSCLC) immunotherapy. Methods: From January to July 2018, a total of 51 lesions from 42 patients with advanced non-small cell lung cancer receiving immunotherapy at Shanghai Chest Hospital were selected in this retrospective study. Pre-treatment contrast-enhanced CT-based texture features were extracted by MaZda software. Ten optimal texture features were chosen based on three different methods: Fisher coefficient, mutual information measure (MI) and minimization of classification error probability combined average correlation coefficients(POE+ ACC), respectively. According to the efficacy of the first immunotherapy, 51 lesions were divided into non-progressive disease (non-PD, n=26) and progressive disease (PD, n=25). The differences were tested in each texture feature set between the two groups. The immunotherapy effects of target lesions were analyzed by principal component analysis(PCA), linear discriminant analysis (LDA) and nonlinear discriminant analysis (NDA). The sensitivity, specificity, accuracy, positive-predictive value (PPV) and negative-predictive value (NPV) were calculated. The area under the curve (AUC) was used to quantify the predictive accuracy of the three analysis models for each texture feature set and compare them with the actual classification results. Results: In all of three texture feature sets, the texture parameter differences of Perc.50%, Perc.90%, "S(5, 5)SumEntrp" and "S(4, 4)SumEntrp" were higher in PD group than those in non-PD group (all P<0.05). The classification result of texture feature set chosen by POE+ ACC and analyzed by NDA was identified as the best model (AUC=0.802, 95%CI: 0.674-0.930), and its sensitivity, specificity, accuracy, PPV and NPV were 72%, 88.5%, 80.4%, 85.7%, 76.7%, respectively. Conclusion: Pre-treatment contrast-enhanced CT-based texture characteristics of NSCLC may function as non-invasive biomarkers for the evaluation of response to immunotherapy.

Characterization of Lysozyme-Like Effector TseP Reveals the Dependence of Type VI Secretion System (T6SS) Secretion on Effectors in Aeromonas dhakensis Strain SSU.

The type VI secretion system (T6SS) is a widespread weapon employed by Gram-negative bacteria for interspecies interaction in complex communities. Analogous to a contractile phage tail, the double-tubular T6SS injects toxic effectors into prokaryotic and eukaryotic neighboring cells. Although effectors dictate T6SS functions, their identities remain elusive in many pathogens. Here, we report the lysozyme-like effector TseP in Aeromonas dhakensis, a waterborne pathogen that can cause severe gastroenteritis and systemic infection. Using secretion, competition, and enzymatic assays, we demonstrate that TseP is a T6SS-dependent effector with cell wall-lysing activities, and TsiP is its cognate immunity protein. Triple deletion of tseP and two known effector genes, tseI and tseC, abolished T6SS-mediated secretion, while complementation with any single effector gene partially restored bacterial killing and Hcp secretion. In contrast to whole-gene deletions, the triple-effector inactivation in the 3effc mutant abolished antibacterial killing but not T6SS secretion. We further demonstrate that the 3effc mutation abolished T6SS-mediated toxicity of SSU to Dictyostelium discoideum amoebae, suggesting that the T6SS physical puncture is nontoxic to eukaryotic cells. These data highlight not only the necessity of possessing functionally diverse effectors for survival in multispecies communities but also that effector inactivation would be an efficient strategy to detoxify the T6SS while preserving its delivery efficiency, converting the T6SS to a platform for protein delivery to a variety of recipient cells. IMPORTANCE Delivery of cargo proteins via protein secretion systems has been shown to be a promising tool in various applications. However, secretion systems are often used by pathogens to cause disease. Thus, strategies are needed to detoxify secretion systems while preserving their efficiency. The T6SS can translocate proteins through physical puncture of target cells without specific surface receptors and can target a broad range of recipients. In this study, we identified a cell wall-lysing effector, and by inactivating it and the other two known effectors, we have built a detoxified T6SS-active strain that may be used for protein delivery to prokaryotic and eukaryotic recipient cells.

Contact-independent killing mediated by a T6SS effector with intrinsic cell-entry properties.

Bacterial type VI secretion systems (T6SSs) inject toxic effectors into adjacent eukaryotic and prokaryotic cells. It is generally thought that this process requires physical contact between the two cells. Here, we provide evidence of contact-independent killing by a T6SS-secreted effector. We show that the pathogen Yersinia pseudotuberculosis uses a T6SS (T6SS-3) to secrete a nuclease effector that kills other bacteria in vitro and facilitates gut colonization in mice. The effector (Tce1) is a small protein that acts as a Ca2+- and Mg2+-dependent DNase, and its toxicity is inhibited by a cognate immunity protein, Tci1. As expected, T6SS-3 mediates canonical, contact-dependent killing by directly injecting Tce1 into adjacent cells. In addition, T6SS-3 also mediates killing of neighboring cells in the absence of cell-to-cell contact, by secreting Tce1 into the extracellular milieu. Efficient contact-independent entry of Tce1 into target cells requires proteins OmpF and BtuB in the outer membrane of target cells. The discovery of a contact-independent, long-range T6SS toxin delivery provides a new perspective for understanding the physiological roles of T6SS in competition. However, the mechanisms mediating contact-independent uptake of Tce1 by target cells remain unclear.

Performance improvement of wastewater treatment processes by application of machine learning.

Improving wastewater treatment processes is becoming increasingly important, due to more stringent effluent quality requirements, the need to reduce energy consumption and chemical dosing. This can be achieved by applying artificial intelligence. Machine learning is implemented in two domains: (1) predictive control and (2) advanced analytics. This is currently being piloted at the integrated validation plant of PUB, Singapore's National Water Agency. (1) Primarily, predictive control is applied for optimised nutrient removal. This is obtained by application of a self-learning feedforward algorithm, which uses load prediction and machine learning, fine-tuned with feedback on ammonium effluent. Operational results with predictive control show that the load prediction has an accuracy of ≈88%. It is also shown that an up to ≈15% reduction of aeration amount is achieved compared to conventional control. It is proven that this load prediction-based control leads to stable operation and meeting effluent quality requirements as an autopilot system. (2) Additionally, advanced analytics are being developed for operational support. This is obtained by application of quantile regression neural network modelling for anomaly detection. Preliminary results illustrate the ability to autodetect process and instrument anomalies. These can be used as early warnings to deliver data-driven operational support to process operators.

LncRNA-TMPO-AS1 promotes apoptosis of osteosarcoma cells by targeting miR-329 and regulating E2F1.

OBJECTIVE: This study aims to explore the clinical value and mechanism of lncRNA-TMPO-AS1 in osteosarcoma. PATIENTS AND METHODS: We collected 51 samples of cancer tissues and 51 samples of matched adjacent tissues from 51 patients with osteosarcoma undergoing surgery in our hospital from February 2018 to February 2019. The expression of TMPO-AS1 in tissue samples was tested to analyze its value in the diagnosis and prognosis prediction of osteosarcoma. We transfected osteosarcoma cells with stable and transient vectors containing overexpressed or inhibited genes. Then, we measured cell proliferation by 3-(4,5-Dimethylthiazol-2-yl)-2,5-Diphenyltetrazolium Bromide (MTT) assay, cell invasion by transwell assay, and cell apoptosis by flow cytometry (FCM). The relationship between TMPO-AS1 and miR-329 or between miR-329 and E2F1 was determined by the Dual-Luciferase reporter (DLR) assay. RESULTS: TMPO-AS1 was up-regulated in osteosarcoma cells. Serum TMPO-AS1 could work as a diagnostic marker for osteosarcoma, with an area under the receiver operating characteristic (ROC) curve (AUC) of more than 0.8. Osteosarcoma cells were transfected with siRNA-TMPO-AS1, pcDNA3.1-TMPO-AS1, miR-329-mimics, and miR-329-inhibitor. The results revealed that inhibited TMPO-AS1/overexpressed miR-329/inhibited E2F1 suppressed the proliferation and invasion of osteosarcoma cells and enhanced cell apoptosis. The DLR assay demonstrated that TMPO-AS1 could target miR-329 and miR-329 could target E2F1. In vitro experiments revealed that TMPO-AS1 could regulate the progression of epithelial-mesenchymal transition (EMT) in osteosarcoma through the miR-329/E2F1 axis. CONCLUSIONS: TMPO-AS1 can function as a diagnostic and prognostic marker for osteosarcoma. LncRNA-TMPO-AS1 can promote apoptosis of osteosarcoma cells by targeting miR-329 and regulating E2F1, which is a potent treatment option for osteosarcoma.

TssA-TssM-TagA interaction modulates type VI secretion system sheath-tube assembly in Vibrio cholerae.

The type VI protein secretion system (T6SS) is a powerful needle-like machinery found in Gram-negative bacteria that can penetrate the cytosol of receiving cells in milliseconds by physical force. Anchored by its membrane-spanning complex (MC) and a baseplate (BP), the T6SS sheath-tube is assembled in a stepwise process primed by TssA and terminated by TagA. However, the molecular details of its assembly remain elusive. Here, we systematically examined the initiation and termination of contractile and non-contractile T6SS sheaths in MC-BP, tssA and tagA mutants by fluorescence microscopy. We observe long pole-to-pole sheath-tube structures in the non-contractile MC-BP defective mutants but not in the Hcp tube or VgrG spike mutants. Combining overexpression and genetic mutation data, we demonstrate complex effects of TssM, TssA and TagA interactions on T6SS sheath-tube dynamics. We also report promiscuous interactions of TagA with multiple T6SS components, similar to TssA. Our results demonstrate that priming of the T6SS sheath-tube assembly is not dependent on TssA, nor is the assembly termination dependent on the distal end TssA-TagA interaction, and highlight the tripartite control of TssA-TssM-TagA on sheath-tube initiation and termination.

Defending against the Type Six Secretion System: beyond Immunity Genes.

The bacterial type six secretion system (T6SS) delivers toxic effector proteins into neighboring cells, but bacteria must protect themselves against their own T6SS. Immunity genes are the best-characterized defenses, protecting against specific cognate effectors. However, the prevalence of the T6SS and the coexistence of species with heterologous T6SSs suggest evolutionary pressure selecting for additional defenses against it. Here we review defenses against the T6SS beyond self-associated immunity genes, such as diverse stress responses that can recognize T6SS-inflicted damage and coordinate induction of molecular armor, repair pathways, and overall survival. Some of these stress responses are required for full survival even in the presence of immunity genes. Finally, we propose that immunity gene-independent protection is, mechanistically, bacterial innate immunity and that such defenses and the T6SS have co-evolved and continue to shape one another in polymicrobial communities.

Differential Cellular Response to Translocated Toxic Effectors and Physical Penetration by the Type VI Secretion System.

The type VI secretion system (T6SS) is a lethal microbial weapon that injects a large needle-like structure carrying toxic effectors into recipient cells through physical penetration. How recipients respond to physical force and effectors remains elusive. Here, we use a series of effector mutants of Vibrio cholerae to determine how T6SS elicits response in Pseudomonas aeruginosa and Escherichia coli. We show that TseL, but no other effectors or physical puncture, triggers the tit-for-tat response of P. aeruginosa H1-T6SS. Although E. coli is sensitive to all periplasmically expressed effectors, P. aeruginosa is most sensitive to TseL alone. We identify a number of stress response pathways that confer protection against TseL. Physical puncture of T6SS has a moderate inhibitory effect only on envelope-impaired tolB and rseA mutants. Our data reveal that recipient cells primarily respond to effector toxicity but not to physical contact, and they rely on the stress response for immunity-independent protection.

Publisher Correction: Intramolecular chaperone-mediated secretion of an Rhs effector toxin by a type VI secretion system.

An amendment to this paper has been published and can be accessed via a link at the top of the paper.

Intramolecular chaperone-mediated secretion of an Rhs effector toxin by a type VI secretion system.

Bacterial Rhs proteins containing toxic domains are often secreted by type VI secretion systems (T6SSs) through unclear mechanisms. Here, we show that the T6SS Rhs-family effector TseI of Aeromonas dhakensis is subject to self-cleavage at both the N- and the C-terminus, releasing the middle Rhs core and two VgrG-interacting domains (which we name VIRN and VIRC). VIRC is an endonuclease, and the immunity protein TsiI protects against VIRC toxicity through direct interaction. Proteolytic release of VIRC and VIRN is mediated, respectively, by an internal aspartic protease activity and by two conserved glutamic residues in the Rhs core. Mutations abolishing self-cleavage do not block secretion, but reduce TseI toxicity. Deletion of VIRN or the Rhs core abolishes secretion. TseI homologs from Pseudomonas syringae, P. aeruginosa, and Vibrio parahaemolyticus are also self-cleaved. VIRN and VIRC interact with protein VgrG1, while the Rhs core interacts with protein TecI. We propose that VIRN and the Rhs core act as T6SS intramolecular chaperones to facilitate toxin secretion and function.